Comfort / Noise with Single-Zone Heat Pump System
Hi there. New to this forum, I was referred over here to get feedback on an hvac system I’m considering for my house.
For context my 2-storey detached brick house in Toronto (climate zone 5/6) is 1500 sqft, excluding basement, built in 1966 and has had some updates done in the 90s which appears to include some wall and attic insulation. The hvac system is Lennox from 1994 and consists of a 92% efficient 50kbtu/h single stage / single speed gas furnace and traditional 2 ton air conditioner.
As the system is quite old I’m starting to research options for replacement. Several local dealers are proposing a Carrier system consisting of a 2-ton 38MARBQ outside unit and a 60kbtu/h 59TP6 furnace. I’ve done some reading about heat pumps and hybrid systems and I like what I’m reading. The package also qualifies for a $5,000 government rebate, so I’m tempted to have this installed. However, I am not so experienced with hvac and none of my friends have installed heat pumps, so I’m not sure if I should proceed right now with this. My biggest question with the 38MARB + 59TP6 is whether maintenance/reliability will be a concern (installation quality is a known factor so I will choose a reputable dealer, I’m just wondering about the equipment itself, all else being equal) and also performance. I have learned that the 38MARB will run the blower at a fixed speed due to the non-communicating nature of this system (see: https://www.youtube.com/watch?v=63Tm_wmp060). Is this a good thing or a bad thing? I am not really concerned about energy efficiency as it sounds like this system will be much more efficient than my old one, but just wondering about comfort and noise… am I going to have a worse experience than if the system was communicating and the blower able to vary its speed?
Any insight would be very much appreciated.
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Replies
tkzz,
I am not an HVAC expert but even HVAC experts will vary widely in their opinions. Certainly Carrier (and related company Bryant) have confidence in this equipment (or at least I hope so). I take an analytical approach to this, which you may or may not appreciate.
You asked:
My biggest question with the 38MARB + 59TP6 is whether maintenance/reliability will be a concern
Comment:
It is hard to find reviews online and maybe you already found this Reddit thread.
https://www.reddit.com/r/hvacadvice/comments/tckljb/carrier_ductless_hybrid_solution_with_forced_air/
Further down, I do provide a link to a review for the furnace.
For sure, Carrier is a big name with a proven track record. Carrier also publishes technical info on this particular unit. It says "Inverter systems provide additional reliability due to the soft start.
This refers to the ability of the inverter to start the compressor motor using reduced voltage and reduced current. This feature is beneficial from an electrical standpoint (eliminates current spikes) as well as an overall reliability standpoint due to reduced stress on all associated system components." What Carrier says is true for just about all modulating heat pumps but it helps us understand why these heat pump units are considered reliable.
You mention:
I am not so experienced with HVAC and none of my friends have installed heat pumps, so I’m not sure if I should proceed right now with this.
Comment:
I found this online "The truth however is that heat pump technology has been established for more than 150 years and the first ground source heat pump was brought into use more than 70 years ago."
Link below:
https://finn-geotherm.co.uk/the-history-of-heat-pumps/
You mention:
I have learned that the 38MARB will run the blower at a fixed speed due to the non-communicating nature of this system.
Comment: The system is classified as non-communicating - that is true. But just so we are on the same page, the Carrier press release states: "The combinations come to life with patented 24V interface technology that connects the indoor and outdoor units to perform seamlessly." So there is still some very basic "communication" happening.
Link to press release:
https://www.carrier.com/residential/en/us/news/news-article/carrier-introduces-ductless-single-zone-hybrid-solutions.html#
You can also read about communicating vs. non-communicating systems. This web page below suggests that the non-communicating systems, like the one you are looking at, are simpler and more reliable.
Link below
https://www.pickhvac.com/central-air-conditioner/extras/communicating-vs-non-communicating/
You asked:
Running the blower at a fixed speed due to the non-communicating nature of this system (see: https://www.youtube.com/watch?v=63Tm_wmp060). Is this a good thing or a bad thing?
Comment: These companies will obviously provide consumers with reasons to select a "communicating " system with a variable speed blower. If we stick with Carrier as a source of info, we can look at how they sell their variable speed blowers:
"If you are interested in more uniform heating throughout your home without the up and down temperature swings of traditional systems, consider a furnace with a variable-speed blower. A variable-speed blower can provide better control over airflow all year during both heating and cooling, it operates quietly on its lower speed settings, and it can help with humidity control as a part of your air conditioning system."
https://www.carrier.com/residential/en/us/products/furnaces/buying-a-furnace/index.html
The selling feature for a single/dual phase blower motor... well it is less expensive.
You mentioned:
I am not really concerned about energy efficiency as it sounds like this system will be much more efficient than my old one, but just wondering about comfort and noise… am I going to have a worse experience than if the system was communicating and the blower able to vary its speed?
Comments:
1. Energy efficiency: I agree with you. We are likely talking about the energy efficiency that you could gain if you had a variable speed blower. I would trust Carrier, as you understood, that this 38MARB hybrid system is very efficient compared to many other systems. Afterall, Carrier does provide specific energy savings figures.
2. Comfort and noise:
2. a) Comfort:
Consider of these theoretical combinations:
i) Non-modulating furnace, single or dual phase/speed blower
ii) Non-modulating furnace, fully variable speed blower
iii) Modulating furnace, single or dual phase/speed blower
iv) Modulating furnace, fully variable speed blower
v) Modulating heat-pump combined with non-modulating furnace, single or dual phase/speed blower.
vi) Modulating heat-pump combined with non-modulating furnace, fully variable speed blower.
vi) Modulating heat-pump combined with modulating furnace, fully variable speed blower.
The variable speed blowers can offer more comfort, in particular when the furnace "burner" is not able to modulate the amount of fuel that it consumes to produce heat. The YouTube guy and Carrier explain that the "variability" or “modulation” with the hybrid 38MARB system comes from the ability of the 38MARB heat-pump to modulate energy consumption instead of having a variable speed blower fan in the furnace.
Carrier will still say that a variable speed blower does have some impact on the level of comfort... because they need to be able to sell their more expensive integrated systems.
2. b) Noise: Well this is "relatively" easy.
The outdoor unit is quiet - look at the related YouTube videos - but those are sitting on the ground. They transfer a little bit more noise if they are on an L-bracket attached to the exterior wall of the house.
Consider where is your furnace located in your house? Is it in a spot that will easily transfer fan noise to your living space? Will the sudden surge of air from the single speed blower motor make your air ducts creak on start up? I doubt it but you could ask your HVAC guy/gal to provide their input.
Also, look at what Carrier says in their literature: "The acoustical insulation in the blower compartment reduces air and motor noise for quiet operation."
Link:
https://www.shareddocs.com/hvac/docs/1009/Public/03/59TP6B-03PD.pdf
Also look at this webpage that review the 59TP6. They have a table on the page to compare different furnaces. They clearly show in this table that the "acoustical insulation in the blower compartment" is something that will result in lower noise levels.
Link:
https://indoortemp.com/resources/carrier-59TP6-gas-furnace-review
If you want to know more about the noise levels from the 59TP6, just call or write Carrier. Ask for the sound rating in decibels from the furnace -> for the specific blower fan speed setting when paired with the 38MARB.
Thanks mr_reference, your wealth of links has been helpful in my research. Some of them I've read already. I am also hoping to hear from some people with personal experience with this equipment. I guess it's fairly new since I have not been able to come across many personal accounts.
One thing is clear is that the communicating system is a lot more money, and the communicating version of the carrier heat pump outdoor unit is much larger... I'm also not so keen on too much technology in my hvac system.
However, it's not totally clear to me how the variable ecm motor behaves in the 59TP6 furnace. It is listed as variable, but is it somewhat handicapped when the system isn't a "fully" communicating system? Or is the 24v interface as you described, going to get me pretty close to the ideal while saving a bundle?
I have a reply below about going to a full electric system but you have two other questions hear so I will reply.
You mention:
It is listed as variable, but is it somewhat handicapped when the system isn't a "fully" communicating system?
Response: I was only able to answer with the limited info that Carrier provided in the press release. If I were you, I would call Carrier directly and "press them to release" the details before you buy the equipment. I find it a big cagy how they are sparse with the granular details you and I were looking for. This said, they are clear that the fan is set to one speed in their literature for this setup but it just seems like a waste of a good fan motor if the fan motor is capable of a variable speed.
You asked:
... is the 24v interface as you described, going to get me pretty close to the ideal while saving a bundle?
Response: The only descrition I have on the interface is what Carrier has online. I don't have the quotes you received so it is hard for me to say. You are lucky to have the government rebate. I have a new system in a new space so I did not qualify.
I will tell you that I paid around $12K CAD (am I allowed to share this info here?) for my 1.5 ton cold climate heat pump combined with the corresponding 1.5 ton air handler. This included the 5KW heat strip and the install of the equipment. The air ducts were done by a separate company so this is similar to your situation. I had a quote from another company for 15% more. I had yet another company that was 40% higher with their quotes.
Keep in mind that my duct work was designed specifically for the unit I selected so my setup is suppose to be as efficient and effective at heating/cooling as these units can get.
Hi tkzz,
Maybe an expert will weigh in on your question. I was just wondering, why not skip the furnace altogether and go all electric? This way you can install the 40MBAB air handler that synchronizes with the 38MARBQ outdoor unit.
We've installed the 38MARBQ24AA3+40MBAAQ24XA3 combo and are happy with it so far. We live in Western MA in a similarly sized house as yours. We've installed an electric backup heat strip for those polar vortex days.
+1 On the proper indoor/outdoor unit combo. There is no need for gas backup in zone 5, a right sized hyper heat will easily carry the place. I use a pair of the Midea Advantage (the Carrier unit is a rebaged Midea Excel) hyper heat units for heat in Toronto without any issues. No gas or electric resistance backup.
I would highly doubt your place needs a 60BTU of heat, I would run through the calculations to figure out what you actually need and size from there.
https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler
Thanks for your input!
Very interesting article for calculating size. Unfortunately It's all a bit over my head, and after having 5 different hvac contractors visit the house, it's clear that none of them will do the calculation either :(. I do have a gas bill from March , would you know of a more user friendly method to calculate furnace size based on this? However I can't remember my thermostat setting in March as we weren't living in the house yet, I think I had lowered it to 18 C.
Do your own calculation! The BetterBuiltNW sizing tool is very easy to use (even HVAC contractors can handle it! :-) ), and has appropriately aggressive default U-factors for different construction types.
https://betterbuiltnw.com/hvac-sizing-tool
Take your time- if you can run a tape measure you can do this!
Nothing makes a bigger difference on comfort than getting the sizing right. For a non-modulating gas furnace don't go any bigger than 1.4x the design load. For a a heat pump make that 1.2x max. As long as there is backup such as strip heat (or a gas-burner), even 0.9x the load at the 99% design condition is fine, and uses less electricity than 1.5x oversizing ( for most systems.)
The 38MARBQ series are re-labeled modulating Midea heat pumps. Midea is currently the world's largest vendor of modulating heat pump/AC systems, and pretty much all of Carrier's modulating heat pumps are now Midea on the inside, even when wrapped in Carrier sheet metal. Carrier got in bed with Midea about a decade ago, and Midea got into bed with Toshiba now more than 20 years ago on a joint-venture in China making Toshiba's refrigeration compressors (everything from dorm-refrigerator sized to industrial rooftop HVAC). The compressors are all Toshiba designs, even if the coils valves & controls may be from other vendors, depending on which system is in use. Carrier has some "Carrier-only" versions of modulating mini-split heads & air handlers, but as I understand it it's all fundamentally Midea hardware, at least on their modulating systems.
Thanks, great resource, I will work through that!
Interesting about Midea. I recently got a midea dehumidifier for my basement. Seems like a decent device, heavy built.
How are Bosch heat pumps in comparison?
Thanks @noew that is very interesting you went with an all electric setup. None of the hvac contractors have proposed this but they might just be behind the curve a bit here.
How cold does it get where you are? We sometimes get -25 in the worst of winter and very occasionally -30 Celcius. Toronto/Canada
tkzz, I responded above based on the setup you were quoted and you were asking about.
I actually went all electric with a Mitsubishi cold climate heat pump and a Mitsubishi air handler inside. The 2 units fully communicate! I am 4-5 hours north-east of you in our nation's capital. Because we can get some -35C weather here on occasions, I put a 5KW heat strip in my air-handler.
My own goals are to eventually eliminate the fixed monthly cost of having gas services to my house and I also want to eliminate all possibility of co2 issues for the sake of my family's safety. Since the ON grid uses natural gas to produce lots of our electricity, it is hard for me to argue that I am going electrict to save the planet.
All except for one company that quoted our job wanted us to stick with a gas furnace. I finally understood that it is what they do day in and day out. It is what they know. You should also note that a few confirmed (confessed?) that they oversized the gas furnaces as a standard practice because they don't want a call back with the client saying "my house is toooo cold". I had a professional calculate my BTU requirements so I was not going to oversize. All this to say that I agree that you should try to figure out your BTU requirements and right size the equipment.
Keep in mind that if you "right size" the cold climate heat-pump and add a heat strip, you will be vastly oversizing your unit for the average day and night. This is acceptable because the system "modulates" the energy it consumes. The heat strip is a sort of insurance policy.
Thanks again @mr_reference_Hugh! Bold move to go all-electric, I admire that. If it works for you in Ottawa then it can definitely work for me in Toronto. Does your electric bill for heat cost more than if you heated the house with gas, and if so how much more?I'm also wondering about the defrost cycles, how often do they happen and do you notice any impact to your indoor comfort during these cycles?
I'm finding it pretty hard to find an intelligent hvac contractor who will take the time to right size the equipment. I've had 5 different ones through my house already and all of them are just eyeballing it.
BTW do you have any fresh air supplementary system in your house such as an ERV?
Context:
Ours is a new build
R90 roof
R40 walls
Air tightness an unbelievable sub 0.20 ACH50
European windows
This is an addition the size of a house on the back of a very small home.
While it is an addition, it is essentially isolated in terms of HVAC. The HVAC is entirely new for the addition, but the pre-existing air-leaky poorly-insulated old 1930s house still has the orginal gas furnace.
(I will not get into details why we need this extra space but it is not just for fun.)
You mention:
I'm finding it pretty hard to find an intelligent hvac contractor who will take the time to right size the equipment. I've had 5 different ones through my house already and all of them are just eyeballing it.
Response:
- Would use an online tool and calculate it yourself as a fisrt point of reference. Dana provided this link in his reply above.
https://betterbuiltnw.com/hvac-sizing-tool
The result should be in BTU/hr required to heat at a specific temperature. A logical result would be between 35,000 btu/hr and 50,000 btu/hr for the temperature you experience on the coldest days (the result is always based on a selected temperature.)
- You can relatively easily verify the results of the online tool using the AVERAGE BTU/Hr you actually have required in the past by looking at your older Enbridge bills.
Step 1. Find the total cubic meters of natural gas used during the heating season using historical billing info. The picture attached is from an old Enbridge invoice from the time they still sent out paper invoices. Enbridge must have your historical consumption data so just call and ask them.
Step 2. Know that 1 cubic meter of natural gas provides a specific amount of BTUs.
Good reading: https://opentextbc.ca/mathfortrades2/chapter/metric-and-imperial/
1 cu.m. = 35,915 BTUs
Source: https://www.energir.com/en/major-industries/conversion-factors/
Step 3. Multiply the number of cubic meters used for a period (month, multiple months, or a year) by the 35,915 figure. Now you have the amount of BTU that you need to heat for a year. You can save this number as a reference point.
Step 4. You want to actually focus in on the shortest period of time for which you have data. So you can focus in on the coldest month of the year (January or February???). Multiply the cubic meters used x the 35,915 figure.
That is the total BTU used in that month. (a large number)
Step 5. Take the total number of BTUs and divide by the number of hours in the month (January has 31 days vs Feb 28 days) so each month is different. Now you have an AVERAGE BTU/hr for the month. Normally, this is not to be used to size your unit because this is an average. Normally the calculations are done for a specific outside temperature (like with the online tool).
Step 6. Compare the AVERAGE actual BTU/hr usage to what is provided by the online calculator tool. See if it makes sense. Remember, the online tool is for whatever temperature you input, not the average temperature for the month of January. The online tool will have a higher BTU/hr if you put the most extreme temperature you need to deal with - which is normally how it is done.
Step 7. Using the average BTU/rh may not be a bad idea. If you have a heat-pump with a backup heat source (gas or heat strip) then you can use a figure close the AVERAGE BTU/hr you found. Again, very few people will do it this way. Remember that heat-pumps (and other HVAC equipment) work better when they run for long periods of time. Using the AVERAGE BTU/Hr will be "under sizing" the unit based on the lowest temperature you will need to deal with a few days per winter. By under sizing, your unit will run for extended periods of time, what you want. By having a backup source of heat (heat strip, infrared heating panels on the ceiling, gas powered furnace, etc.) you will never be cold.
- Note that only a few will be trained to do this, but many are focused on either sales or installation. Very often the strategy is simply to oversize. Each trade has their own focus.
Step 8. You can determine how much it would cost you to go ALL electric fairly easily. Once you have the total BTUs you use in a year, then you can convert the BTUs to Kwh. Here is a tool.
https://www.rapidtables.com/convert/power/kW_to_BTU.html
The answer is 1 Kwh = 3,412.142 btu/hr
Note: In all of this, you will need to remove a number of BTU if you have other gas appliances. Normally for things like hot water heaters, the manufacturer will specify the amount of energy required for their product per year (for a typical household). Just call the manufacturer if you can't find the data online. Subtract the figure but don't worry if it is too high or too low. Just use what you find from the manufacturer.
Step 9. Divide your total BTU usage by the number of BTU/Hr you found in step #8 which is 3,412.142 btu/hr. Now you have the total number of kilowatts you need per year.
Step 10. Look at your electrical bill and find out the cost of your electricity. If you are charged depending on the time of day you use electricity, you should remember that the HVAC equipment will typically be used more in the evening and night (colder and no sun to warm through windows). You should also have a history of "time of use" data by month for the past year on each bill if you want to get an average price of electricity based on your actual usage.
Step 11. Once you figure out what cost per Kwh from your utility bill, just multiply that figure by the number of Kwh you need to heat your home for the entire season.
You asked:
BTW do you have any fresh air supplementary system in your house such as an ERV?
Response: Yes, we have the Panasonic IntelliBalance 100 cold climate version. It is rated to be very quiet. It has really good efficiency rating (energy consumption) and effectiveness ratings (how much work it can perform). I also chose it because it is very slim and I needed that for my application.
Thank you again- amazing tips!
We got the keys to the house on March 1st, so I only have data for March and later. I ran through the calculation for March and got 16,700 BTU/h. This includes the hot water heater however we were not living in the house in March so there may not be much of an impact there. Also I can't remember the thermostat setting that I set for March, it may have been 18 degrees as we weren't living in the house yet and I remember lowering the temperature. In any case the number is way lower than the 60,000 BTU/h rating of the proposed furnace! Definitely makes me think.
On the other hand I started to run through the calculations with the betterbuiltnw tool. I inputted all my details including rooms and windows but ran into a snag on the System tab. Heating input is clear, I inputted 60,000 for 'input' and 96% of that (57600) for the 'output'. But I have no idea what to input for the Sensible and Latent cooling numbers. I am using the 38MARB as my example but couldn't find this particular data. The proposed size was a 2-ton, I believe this works out to 24,000 btu/h, but how does this translate into the Sensible and Latent fields?
The BTU -> kW conversion is a little confusing as sometimes we deal with an hourly rate and sometimes with the net amount for a longer period. I think I figured it out and got back to the monthly amount of electricity that would be used. According to my numbers, heating the house with electricity in March would have been more than double the cost of gas. (Gas charges for March = $141.93; Theoretical electricity charge = $293.67 using a rate of 10 cents per kW). Does this seem crazy?
Thank you again.
Update: I think I managed to figure out the sensible/latent numbers. Carrier's specs for the 38MARBQ have a table showing the Total Capacity and Sensible Capacity for various indoor / outdoor temperatures. I grabbed a typical scenario of 30 degrees celcius outdoor and 24 celcius indoor and then subtracted the sensible from the total to get the latent. IS this right?
Here is what I got from the betterbuiltnw tool. I had to guess some of the numbers such as the R value of my wall insulation. But it looks like the hvac companies' idea of a 60k furnace may be fine? 2-stage plus heat pump should ensure that the right amount of heat is delivered for various times in the year. The second image shows the heating performance with the heat pump. It looks like it would work well until freezing, below which I'll need the backup. Cooling is oversized according to the report but a variable heat pump should help with that I think?
I'm in Toronto and heating with gas and a heat pump with a COP of 3 is about the same cost. I can't see it being much different there, if anything your electricity is cheaper as you can get some of the sweet low cost Quebec hydro.
The output from the betterbuiltnw feels to be on the high side. I wouldn't trust the March fuel use data since it wasn't a very cold month. It also would have been much higher if the betterbuiltnw model was correct.
I'm in Toronto as well! Probably no Quebec juice for me...
I included my finished basement in the square footage, which brought the total to 2100 sqft, perhaps that's the reason for the higher load vs my original mention of 1500 sqft. In-laws are sometimes staying over in the basement bedroom so I can't really exclude it. :) Here is the list of rooms...
Post the room loads, we can go from there to see what looks off.
What is the wall insulation and windows in the house currently? Any insulation in the basement?
Sure, thanks so much for looking at this for me!
I noticed fiberglass looking stuff in the walls in the whole house. The basement walls filling looks older to me. Overall it doesn't look very modern but at least the walls aren't empty. I guesstimated the walls as R-11, and left the basement as 'default.
If your basement walls have insulation, add that in. Basement losses should not be that large.
A clear double pane window is R2, so U0.5. If there is lowE coating on them than even lower (lowE glass is usually darker and reflective).
The default wintertime leakage works out to about 14ACH@50PA. That is very leaky uninsulated balloon frame house. I would guess about 1/2 that is reasonable for a house with a simple flat ceiling.
Alright, I upped the basement to R-11 and the windows to R2 (they are double pane, but older from the 90s and not working so great...getting a little condensation already and it's still above freezing outside).
For ACH in this tool, the allowable range is 0.06 to 2... default is 0.7 winter and 0.4 summer. If you're suggesting 7 ACH how do I input this? Thanks!
That is the natural air changes per hour of the structure. The ACH@50PA I mentioned earlier is the leakage when doing a blower door test. Since the pressure is much higher, the leakage is larger.
There is no proper way to convert from ACH@50PA to natural ACH, the about close enough guess is the N-factor:
https://www.greenbuildingadvisor.com/question/what-is-n-factor
So in your case with a single story structure, in cold climate you divide the 7ACH@50PA by 22, so use 0.3.
You can also play with the model to see what effect reducing this air leakage has on your heating needs.
Great, thanks for explaining that.
I used an N-factor of 14.8, since I have a 2 storey house in Zone 2... New ACH(nat) is 0.5 instead of 0.7. This reduced the required heating by about 3,000 btu/h.
Here's the chart after updating basement insulation, window and ACH. Now the heating requirement tops out at closer to 40,000 BTU vs the original 60,000. I used a Carrier 59TP6 with 38,400 btu/h output. How does this look to you?
The other question is do I trust all these calculations, some of which are not entirely scientific...
For the n-factor conversion use the number of stories above grade, so even though there is a basement, it is still a one story house. Won't change the numbers much but gets it closer to what I would expect for a 2x4 insulated house that size (under 20 btu/sqft).
If you want to get closer, you can wait a season with the equipment swap and get fuel use data from a cold month.
Anything 60000BTU is way oversized, finding a smaller fuel burner will take some work as they are not so common. A 40000BTU two stager should more than cover but I would not be surprised if your fuel use numbers come in well bellow that so that something like a small 30000BTU unit will cover your load with room to spare.
I haven't looked in detail at any of the gas+heat pump options, can't help you much with the Carrier VS Bosch. I've used the Midea units, they OEM the 38MARBQ outdoor unit, so far they have worked great.
I guess I wasn't clear before - my house is 2 storeys above grade plus the basement below. 3 x 700 sqft approximately.
I might end up waiting a season since it's tough to make a decision without anything urgent forcing me to :)
Bosch furnaces start at 60,000 BTU so if I need a smaller one, I'd be going with Carrier (40,000 BTU). If the bigger furnace can operate on a lower stage, would the larger furnace then not be so much of an issue? Also, would the 1/2 HP blower in the smaller furnace be adequate for air conditioning vs the 3/4 HP in the larger one?
Good to know you have positive experience with the Midea (Carrier) 38MARBQ!
The low stage on most 2 stage furnaces is not that low. I had a 60k unit in a larger uninsulated double brick house (much higher load than yours) that never had to go past the first stage to keep the house warm.
The problem with oversized units is the runtimes are very short, you get a burst of hot followed by long wait times where you can feel the walls sucking the heat out of you. Not the best for comfort.
This might not be so bad with a heat pump added in as you can run the heat pump instead of the burner during shoulder season. I think the Carrier/Midea units connect using their relay module to the standard furnace, this means the outdoor unit will modulate so it should provide more even heat.
You don't want an oversized fan for cooling use. Too much airflow and you get almost no humidity removal. A 2 ton unit only needs about 700CFM of airflow, so even the smaller 40000BTU Carrier 59TP6 unit provides more than enough.
The issue with cooling in these older homes is there is typically no return on the 2nd floor, or even if there is it is not high on the wall. Without this, you get a lot of stratification thus pretty hot bedrooms. Unfortunately not easy to retrofit if not there, ceiling fan can help but won't do miracles. Throwing more cooling at it won't help, you end up with a colder main floor and icebox in the basement.
You are doing the right thing by thinking about your options ahead of time, a bit of research will means you'll end up with a more efficienct setup in the end.
I got one more quote just today for a Bosch system. Bosch's smallest furnace is a 60kbtu so it's the BGH96M060B3B plus a 36kbtu heat pump model BOV-36HDN1-M20G. Cost is roughly $3,800 more than the Carrier system.
It would be great to hear from anyone experienced with both Carrier and Bosch which system is the one to get. I value reliability, low noise, and comfort. I'm sure either system will be very efficient compared to my old stuff so I would not consider efficiency in the decision between the two brands.
Thanks again for your insight @AKOS TOTH!
Luckily my house DOES have a return duct at the ceiling height on the 2nd floor. It's roughly in the middle of the house in the upper hallway. During the summer I found the A/C to work very well (2-ton unit).
You have a good point about humidity removal... this is a huge benefit to feeling comfortable in the summer. If my system would run longer it would be better for sure. Perhaps I wouldn't have to run a dehumidifier in the basement.
All of this sort of points to maybe getting the 40,000btu carrier with the 38marbq heat pump. The only downside of this system seems to be not a lot of heat pump capacity for heating, so if I ever wanted to ditch gas I'd probably have to upsize the heat pump. With the Bosch 3-ton HP I should be able to heat the house better without gas if needed. However if I go with the bosch, Their smallest furnace is 60,000btu.
I found an interesting article that describes an alternative method for sizing a heat pump. I assume this would work for furnace sizing too.
https://carbonswitch.com/heat-pump-sizing-guide/#Why-correctly-sizing-a-heat-pump-matters
What do you think of this?
The most accurate way to size equipment is based on fuel use. About the only unknown in that case is equipment efficiency which tends be near label unless there is something seriously wrong with the unit.
Thermostat runtimes can be used but you need to do a lot of averaging as it is a pretty noisy signal. It will get you into the ballpark though.
Man J has to make some assumptions about the building so the loads tend to be always overestimated.
I'm not sure the Bosch unit is a good fit in our colder climate. It looses a lot of capacity when it gets colder, this means the 3 ton Bosh does about the same amount of heat as a 2 ton hyper heat. Oversizing by this much will also tend to cause issues in the cooling season.
I would wait till next year to get some better fuel use data and size from there. Based on the recent increase in natural gas costs, keeping a fuel burner is most likely a money looser.
Thanks again for your reply AKOS_TOTH.
The thing about fuel use is that my water heater also uses natural gas, and so does my BBQ. I am leaning towards going the winter with the existing setup and doing the calculations, but I'm not sure how I can isolate fuel use for the furnace. It sounds like I can use the thermostat runtime as another way of estimating but shouldn't rely 100% on it.
Interesting about the Bosch... I looked at the specs more closely (https://budgetheating.com/v/vspfiles/downloadables/BOVA36-60HDN1-M20G%20Technical%20Specifications.pdf) and compared them to the 38MARB (https://www.shareddocs.com/hvac/docs/1009/Public/00/38MARB-01PD.pdf). It seems like the Carrier unit puts out more heat at similar outdoor temperatures, surprising, since it is a side discharge smaller form factor. I also saw that the Bosch uses a GMCC compressor which is a part of Midea. Midea is the company that makes the Carrier unit! It's starting to seem like the Bosch may not be worth the extra dollars. If I go Carrier I could also maybe go with the smaller furnace size.
General question about heat pumps though - how does one right-size a heat pump for heating without over-sizing it for cooling? Would a variable speed compressor not allow for more heat capacity while letting the unit ramp down in the summer?
"how does one right-size a heat pump for heating without over-sizing it for cooling"
You can't really. Modulation does help a bit, not perfect as on min output humidity removal is not great on most units. This is why you always good to check the minimum operating range of the unit.
Generally anything that will do heat in cold climate will be oversized for cooling. The only thing you can do is select a hyper heat unit, most nowadays deliver above their nameplate rated heating capacity. A good example is the 3/4 ton Fujitsu slim ducted unit which puts out almost 1.5 tons of heat at 5F:
https://ashp.neep.org/#!/product/25310/7/25000///0
Hi again !
I am likely going to get the Carrier system as it seems to be a great value and has the option of a smaller furnace. The installer I so far prefer said they will do a heat loss calculation before we decide on a final furnace size.
In the mean time I came across a free software app called HOT2000 which is produced by the government of Canada. I inputted my house characteristics and it has produced a report, which I'm trying to interpret. On page 14 I see the following:
Design Heat Loss* at 2.7 °F (2.09 BTU/h / Ft3): 36821 BTU/h
Would a 40,000 btu/h furnace be adequate? It sorta seems like I should get the 60,000 btu/h 2-stage furnace which, when paired with the 38MARB heat pump, will give me a wider range of heating capacity. I would use the heat pump in shoulder season, the furnace in low stage for the coldest months, and the furnace in high stage for the coldest handful of days.
I'm attaching the pdf of the report in case you feel up to checking it out :)
Thanks!
More info! I put together this chart that includes the heat loss and cooling load of my house (slightly adjusted vs previous due to specific geography) as well as the 2 furnace options (40k and 60k) plus the heat pump (38marbq 2-ton). Based on this, which furnace size do you think I select and why and is the 2 ton heat pump a good choice as well?
I would wait till the spring and get you actual heat loss number. I doubt your place is near the 40k you got. Once you have the actual heat loss you can see how best to supply the heat. At the current utility costs, a right sized heat pump to fully carry your place without gas is the cheaper option.
Just playing devil's advocate here so bear with me. Let's say I wait and find that the heat loss is less than 40k, what would I do then? The smallest furnace that Carrier makes is 40k. The smallest that Bosch makes is 60k. I'm hearing that new hvac installs will be 30% more expensive next year due to changing standards and inflation.
Natural gas futures have fallen already so the economics do not currently point towards an all electric system at least not for the dead of winter.
If I had radiators and not forced air, I think it could be different but I'm not considering that sort of overhaul as adding rads would be costly and the ducts are useful for air conditioning in the summer.
I got my design heating load number... 11.25 kW. Alomst the same as what I got from the betterbuiltnw tool. Blower door is 4 ACH@50 which he said was pretty good.
4ACH is excellent for an older home. 38k BTU/h heat loss for 1400sqft (insulated basements adds very little so it can be mostly ignored) house still feels on the high side, I can't see the place being 27btu/sqft, that is above uninsulated double brick heat loss.
If you update the betterbuilt model to 0.27ACH what does it come back with?
Hey, thanks for staying with me!
Yeah, the technician seemed surprised. But I think it's because a previous owner did some significant updates to the building envelope, it's not the original 1966 situation here. My neighbour on the other hand is an original owner (89 years old guy), and he's still heating with electric baseboards!
Good point re: updating the ACH.
I plugged in 0.27 and now the heating load is 31,438 BTU/hr. That had way more of an inpact than I expected! (Note this is for 1 degree F heating 99% Dry Bulb.)
With a 2 stage furnace and a heat pump to take care of the milder weather, a 40k furnace that outputs 38.5k still seems like a good size to me for a dual fuel system, as it would also allow overnight setbacks on the coldest days of winter.
I'm not sure if I mentioned, I also installed the HOT2000 (Govt of Canada app) and inputted all the specifications, and I get a higher number - 38,730 BTU/h even after dropping the ACH. (Default was actually 4.5 in this app, so I only had to drop it a little).
With some further updates to the insulation and windows I could see how I might be able to actually heat the place fully with the 2-ton heat pump even though it may or may not be economical. This is a good thing as I was a bit concerned about the heat pump being undersized should I want to shut off the gas at some point.
What do ya think?
If you must have gas, the 40000btu plus 2ton hyper heat unit is a reasonable compromize. I really can't see a 4ACH house that size needing more than that.
Without fuel use based heat loss it is hard to say what exactly your load would be, any of the models are simply estimates and they are only as good as the inputs, they will never be spot on.
I would be tempted to go with a 38MURAQ30AB3 (this is the hyper heat 2.5 ton unit) with matching air handler and call it a day. You can add in a small stirp heater (3kW so 10000BTU/h) for polar vortex days plus peace of mind.
The less gas you use the more expensive it becomes, so a bit saved right now is not that much in the long run plus a simpler system is always better.
Thanks again akos!
I will continue my research…
I looked up the model you mentioned, the 38MURA. Specs are very similar to 38MARB. The main difference seems to be that the MURA can be used with an air handler at the larger sizes while the 38MARB is only the 2 ton. For some reason the larger sizes of 2.5 and higher have less HSPF ratings and are not energy star certified, so no rebates available for the larger size even for the MURA. That’s $5000 lost for me right there. I met a new contractor recently who specializes in heat pumps so I will see what he can come up with, maybe something from a different manufacturer. But I’m getting the sense that something is missing in the marketplace when it comes to heat pumps larger than 2 ton…
There are plenty of 2+ ton hyper heat units. Most Asian manufacturers offer a product that comes with a multi position air handler (same as a furnace) and lot of domestic players re-badge these as house brand.
A nice one is Gree Flexx units (these are the OEM for GE and MrCool Universal). Mitsubishi, Fujitsi and Midea all make similar products. Not all will be energy star, so it will take some digging to find the correct one.
This is a good resource for search for models and compering specs:
https://ashp.neep.org/#!/product_list/
If you don't mind doing a bit of ductwork and your existing ducting is not too restrictive, one of these is an excellent option:
https://ashp.neep.org/#!/product/59101/7/25000///0
The Fujitsu equivalent has much better turndown but is not energy star.
Great resources, thank you!
I've been poring over the specs and have found that the 38MARB is decent but drops its output as the temperature falls more than some others. Carrier themselves seems to have a slightly better model, the 38MURA, but I found out it's not available here until next spring.
Using the same database, I was surprised to find that the Bosch units don't perform much better than the Carriers, I suppose they are using similar tech in them.
I had one more installer come to my house and he installs MOOVAIR equipment. He proposed an all-electric system with heat strips as backup. He also installs Fujitsu but thinks that MOOVAIR is just as good, and parts are more readily available here for them. The performance of these is pretty good, better than either of the Carriers, despite it also using Midea guts. https://ashp.neep.org/#!/product/56618/7/25000///0
I'm a bit nervous about:
- A heat pump requiring backup heat for the coldest days... will this not be required in the future when heat pumps become even better?
- The cost of electric resistance backup heat if I don't go for dual-fuel
Well, I think I may be going down the path you originally recommended, which is to keep using my existing system through the winter.... I came close to getting the 38MARB+59TP6 but I guess it didn't feel like the ideal system to go ahead with it just yet. I'm talking to a new contractor who seems to be more experienced and deals with Mitsubishi, Carrier and Amana equipment. I like his approach so far, so we'll see what he proposes.
In the mean time I have mapped out the "actual" energy use of my old furnace based on runtime. It seems like the energy use is lower than what was modelled with software by the energy auditor and the better built tool. Check it out and let me know what you think! https://s3.amazonaws.com/greenbuildingadvisor.s3.tauntoncloud.com/app/uploads/2022/12/16104340/48563_1671205419_energy-chart.png
Hey just updating my thread with the latest progress.
First I really love this site and all of the great folks, particularly Akos, who provided a ton of useful information, which was at first quite intimidating. After several months of reading I have learned a ton. I did my own fuel-use based heat load calculation using winter data and also a thermostat runtime based calculation which lined up with the fuel usage method.
I am now very confident that my design heating load is in the 22,000 - 24,000 BTU/h range - much lower than the old 50,000 BTU/h furnace I have and waaay lower than the massive 60,000 BTU/h furnace that several contractors suggested.
Over the winter my old furnace sprang a couple condensate leaks which I managed to control using various materials found around my house. I also saw how expensive natural gas has become and how it will continue to rise in cost with the carbon tax. I also learned about the compromises with dual fuel systems, particularly around the fan speed of the indoor unit being fixed, and the lower efficiency ratings.
Conclusion is that I ordered a Carrier all-electric system based on the 38MURA 2-ton heat pump and 40MUAA air handler :) The contractor has suggested a 10kw electric backup heat coil, which seems rather large so I may ask them to downsize that to a 8kw or 5kw. In case of emergency, it would be nice for the coils to be able to handle the entire heating load, so maybe 8kw will be ideal.
The installation should be happening later this month, so I'll update this thread once I have it in use. My first experience with it will likely be for Air Conditioning which I'm expecting to be much better than the old and noisy 1994 2-ton single stage lennox cube!
Sounds like a good plan.
One thing to watch is disabling the heat strip on some systems is not easy, lot of times they are configured by default (and revert to it in case of power loss) to run them if the unit is in defrost. This can quickly add up and hard to tell if it is happening. The best is always to turn the breakers off and only enable the strip heater when it is actually needed.
Thanks, that’s good to know. I’ll have to ask about that and keep the breakers off until a deep freeze! Or in case the heat pump dies…
So is it going to be ok if the heat strips don’t run during defrost?
Most heat pumps just turn off the blower during defrost. On ducted unit this is not really noticeable except for the fact that airflow stops for a bit. Before the blower restarts, the coil is re-heated again so there is no cold air from the vents. Having a heated defrost is not really worth the energy penalty.
Hi Akos,
I had my new system installed this past weekend. They ran a single big wire to the air handler. It doesn't seem like I can disable the heat strips separately from the AHU. But the ecobee thermostat seems to manage the aux heat, so I am hoping that'll be enough control. I'll see when winter comes. I will post another comment below with general observations about my new system as there seems to be some issues.
Hey folks
I had my new Carrier 48MUAA / 38MURA system installed this past weekend by an 'award winner' authorized carrier dealer and wanted to follow up with my initial thoughts:
[list=1]
[*] I can't comment on heating yet but cooling is strong during this heat wave we're having.
[*] The new system is way quieter than my old lennox furnace / air conditioner, both indoor and outdoor units are noticeably quieter. Using the [url=https://apps.apple.com/us/app/niosh-sound-level-meter/id1096545820]NIOSH sound level meter[/url] measuring at 1 foot from each device, the before/after measurements are as follows. Old furnace: 64 dB(A) / New air handler: 50 dB(A). Old AC: 70 dB(A) / New Heat Pump: 62 dB(A). Sound measured in a bedroom from bed with old system: 40 dB(A) / Sound at same bed with new system: 33 dB(A).
[*] The airflow / cfm is significantly less on the new system than the old system. This is likely the reason it's so much quieter. The character of the noise is different as well. The old system sounded like an aircraft and the new one almost sounds like the plumbing sound of water running in pipes in the wall.
[*] My 2nd floor is 1 to 2 degrees C warmer than the main floor even after shutting all the basement and main floor registers and fully opening the 2nd floor registers. I did not expect this and will be following up with the dealer about it. I will be upgrading insulation later this year so this could also be the remedy, without changing anything about the HVAC.
[*] The system is turning on/off (short cycling) more than I expected for a variable speed heat pump and air handler. I will be following up with the dealer about this. I am not sure if this is due to the ecobee, the way they wired everything up, or settings on the air handler.
[*] We're currently experiencing a heat wave. I expected more humidity removal. Likely not happening due to the short cycling. Main floor is currently 57% RH.
[*] The 40MUAA has 3 different wiring scenarios, 2 of which are meant for 24v thermostats. The 1st scenario only uses 2 wires between the outdoor and indoor units. However, the installer used scenario 3 which has a full set of wires between indoor and outdoor units. They were not able to explain to me the difference between these the 2 applicable wiring setups, claiming that they function the same. I will be following up with this as well, as I am wondering if the short cycling is due to the way they wired it up.
[*] The ecobee is recommended over Nest by basically all hvac people. But from a user perspective, the ecobee is not as user friendly as my old Nest. I am frankly shocked at the design of the app and how confusing it is. I'm sure I'll eventually get used to it but wow I did not expect it to be so bad.
[*] The 38MURA / 40MUAA system also supports a [url=https://www.siglers.com/wired-remote-control-7-day-programmable627132687.html]communicating controller[/url] which I didn't look into very much since I wanted a smart wifi thermostat with remote temp sensor but I do wonder if the controller would help the system modulate better.
[*] When brazing they did not initially flow nitrogen as promised by the sales person. I had to tell them to do it. This was highly disappointing and was a bit of a turning point in my confidence in the installers. When they connected the nitro tank they also didn't flow for very long before starting to braze. This may be average service for residential hvac installers, which is sad. Curious about others' experience.
[*] The installation looks a little sloppy in some areas (sheet metal not totally straight in some places, small gaps between plenum and AHU not sealed, brazing used excess amount of solder) but I'm pretty detail oriented, and the average homeowner likely wouldn't notice these details.
[/list]
Any insights on the above before I go back to the dealer with my list if questions would be very much appreciated.
Hey folks
I had my new Carrier 48MUAA / 38MURA system installed this past weekend by an 'award winner' authorized carrier dealer and wanted to follow up with my initial thoughts and seek advice on some issues I noticed:
* I can't comment on heating yet but cooling is strong during this heat wave we're having.
* The new system is way quieter than my old lennox furnace / air conditioner, both indoor and outdoor units are noticeably quieter. Using the NIOSH sound level meter app measuring at 1 foot from each device, the before/after measurements are as follows. Old furnace: 64 dB(A) / New air handler: 50 dB(A). Old AC: 70 dB(A) / New Heat Pump: 62 dB(A). Sound measured in a bedroom from bed with old system: 40 dB(A) / Sound at same bed with new system: 33 dB(A).
* The airflow / cfm is significantly less on the new system than the old system. This is likely the reason it's so much quieter. The character of the noise is different as well. The old system sounded like an aircraft and the new one almost sounds like the plumbing sound of water running in pipes in the wall.
* My 2nd floor is 1 to 2 degrees C warmer than the main floor even after shutting all the basement and main floor registers and fully opening the 2nd floor registers. I did not expect this and will be following up with the dealer about it. I will be upgrading insulation later this year so this could also be the remedy, without changing anything about the HVAC.
* The system is turning on/off (short cycling) more than I expected for a variable speed heat pump and air handler. I will be following up with the dealer about this. I am not sure if this is due to the ecobee, the way they wired everything up, or settings on the air handler.
* We're currently experiencing a heat wave. I expected more humidity removal. Likely not happening due to the short cycling. Main floor is currently 57% RH.
* The 40MUAA has 3 different wiring scenarios, 2 of which are meant for 24v thermostats. The 1st scenario only uses 2 wires between the outdoor and indoor units. However, the installer used scenario 3 which has a full set of wires between indoor and outdoor units. They were not able to explain to me the difference between these the 2 applicable wiring setups, claiming that they function the same. I will be following up with this as well, as I am wondering if the short cycling is due to the way they wired it up.
* The ecobee is recommended over Nest by basically all hvac people. But from a user perspective, the ecobee is not as user friendly as my old Nest. I am frankly shocked at the design of the app and how confusing it is. I'm sure I'll eventually get used to it but wow I did not expect it to be so bad.
* The 38MURA / 40MUAA system also supports a communicating controller (https://www.siglers.com/wired-remote-control-7-day-programmable627132687.html) which I didn't look into very much since I wanted a smart wifi thermostat with remote temp sensor but I do wonder if the controller would help the system modulate better.
* When brazing they did not initially flow nitrogen as promised by the sales person. I had to tell them to do it. This was highly disappointing and was a bit of a turning point in my confidence in the installers. When they connected the nitro tank they also didn't flow for very long before starting to braze. This may be average service for residential hvac installers, which is sad. Curious about others' experience.
* The installation looks a little sloppy in some areas (sheet metal not totally straight in some places, small gaps between plenum and AHU not sealed, brazing used excess amount of solder) but I'm pretty detail oriented, and the average homeowner likely wouldn't notice these details.
Any words of advice would be appreciated before I go back to the dealer for support.
Experts can weigh in (I'm not an expert), but if you are using an Ecobee wired up as a 24v non-communicating controller, you may not be getting the full variable speed/modulating capabilities of the system. Typically "communicating" systems require a proprietary communicating thermostat to take advantage of modulating fan and compressor capabilities. But I don't know anything about the specific Carrier system that you have, so I suppose it's possible the Ecobee can take full advantage of that one.
Edit: I just googled your system and it looks like a standard 24v controller is the default setup. So it looks like it is designed for use with something like an Ecobee. So that may not be the problem. I just know I've read complaints about variable speed systems that use 24v non-communicating controllers. Poor dehumidification and modulation seems to be at least a somewhat recurring complaint with that type of setup. I would try to get more information on the 3 different wiring setups that you mentioned, and try to find out why they chose the 3rd.
Thank you. I wonder if I should see about getting the communicating controller instead... I was under the impression that the 40MUAA / 38MURA had some internal logic to ramp the compressor / fan up and down, but that doesn't seem to be the case. It appears to be working like my old single stage system.
Take a look at P20:
https://www.shareddocs.com/hvac/docs/1009/Public/0D/IM-40MUAA-02.pdf
No matter what you want the indoor and outdoor unit connection with the 2 wires.
If you want to use something like an Ecobee or Nest, the best you can do is 2 stage cool and 3 stage heat. This is mostly OK, the 2 stage cool works reasonably well, the 3 stage heat seem to be 1 stage of heat pump and 2 stages of AUX, so not really stages. You do have to make sure they actually connected all the stages though.
If you want fully modulation, you need the Carrier communicating thermostat KSACN1001. Again make sure the indoor and outdoor unit are connected using the 2 wires only.
As for the upstairs too warm issues, this is a common problem in older homes as the 2nd floor return is undersized and usually not near the ceiling where you want it. I would try to close off the return in the basement if there is any to get a bit more flow upstairs.
Thank you Akos!
Would you happen to know how the system would behave using the 2 wire indoor outdoor connection? I wasn't able to determine this from the documentation. But I have a gut feeling that there's something different about it.
I wonder how the system would work with the communicating thermostat? It is a midea device and don't believe it supports wifi or remote sensors which might be a real issue in my house with the warm upstairs.
Luckily our 2nd floor return is actually up high near the ceiling, since the ducting was installed (retrofit) in the 90s (see pic). The 2nd floor is approx 700 sqft. But maybe blocking off a basement return could help, thanks for that suggestion.
You can try to see if the Midea KSAIF wifi kit works. There might be a Carrier branded equivalent.
These systems are too new to know exactly how they run. Best you can do is do some testing and let us know.
I think with the 2 wire connection to the outdoor unit should modulate based on the return air temperature even with a single stage thermostat.
Midea units typically have the option to use either the return air temperature sensor or the thermostat sensor for controls. For 2 story house, you can install the thermostat on the main floor, use the thermostat sensor for heat but during cooling season set it to use the return air sensor.
Hey Akos
Thanks again.
I just spoke with my installer/dealer and he said he attended a seminar about this and asked the question about the 24v (scenario 3) vs. 2-wire (scenario 1) and was told that they're functionally identical... He also said that the return air sensor is being used currently. But I am still skeptical about all of this. I don't want to tinker with things myself and don't really have the time either :( The midea thermostat is an interesting option but even with the wifi kit , if it worked, I would still lose the remote sensor feature that ecobee has which has been very useful to control bedroom temperatures at night. I feel like I'm stuck. I pressed my dealer to get some answers about the short cycling which will hopefully lead to something useful...
Without the RS485 communication between the indoor unit and the outdoor unit, there is no way for the outdoor unit to know the return air temperature, so there is no way for it to modulate.
Maybe what they mean is the indoor unit will ramp the fan speed up/down based on return air temp.
Not quite the same thing.
First thing first, I would make sure you have at least the two stages of cooling properly wired, configured (jumpers on the indoor unit and settings on the Ecobee) and running as it should.
"I just spoke with my installer/dealer and he said he attended a seminar about this and asked the question about the 24v (scenario 3) vs. 2-wire (scenario 1) and was told that they're functionally identical..."
These installers might be awesome and might be exactly right. I tend to agree with Akos, though, that if it is not wired for the RS485 communication, I don't see how it can modulate.
Most installers are not awesome and will just tell you whatever they can to get you to go away. Given that it's not operating how you would expect it to, and given that there's decent reason to believe that it's not modulating the way they wired it, I would be skeptical of what they are telling you.
@aunsafe & @akos thanks for your advice… I’m not gonna let this one go with the installers! What you say is logical. I wish there was some hard proof but the carrier manual does not mention the functional differences between wiring scenarios which is disappointing. Some hard evidence would make it a lot easier for me to convince the installer to come and redo the wiring. However I will still try to get them to change it. They will be coming back to install the backup coils as they were on back order so I’ll try to get them to redo the wiring at the same time. If you guys can find any documentation about the wiring that clearly shows the functional differences between scenarios this would be great. Cheers.
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Seems to me Eco bee and Nest do a lot with almost no data. My problem with them is I don’t care about doing the things they are good at. They seem to be good at figuring out when I am away from home and setting back the temp and letting me tell it when I am heading home so it can get the house back to the set point. I don’t care because I think it is a dumb way to operate a heat pump! I think a variable speed heat pump operates best as a set it forget it mode the same temp 24-7 for the whole heating season. Being mostly retired I am rarely away very long.
My Rheem systems communicating thermostat has tons of data but the programers have done very little with in terms of automation and fancy graphs.
It will display the supply air temp, return air temp, indoor coil temp outdoor coil temp, local outdoor air temp, refrigerant pressure high and low, compressor current speed, expansion valve position from 1-100, calculate and display the current super heat. Log any errors with detailed fault codes none of this data is available to the generic systems.
Consider getting the communicating thermostat as it allows the indoor and outdoor units to know what the other is doing and allows the variable speed compressor to use its full range of speeds. The generics can only command off, low and high.
Walta
The main feature I use ecobee for is the remote temp sensor. I put it in my son's room so that the temperature is correct at night. I program the ecobee to only use his bedroom sensor at night. There can a 1 - 3 degree difference between his bedroom which is west facing at the corner of the upper floor, and the living room which is east facing and in the middle of the house. I also like to be able to monitor temperatures on my phone and tick them up or down by a little bit as needed depending on what we are doing in the house (cleaning vigorously vs. watching a movie). I agree with you about the other features - I disable them.
I did a quick read through the manual of the manual and the only option you can't have with the two wire connection is resistance heat during defrost. This is an energy pig anyways and it doesn't create any comfort issues as long as the system is set to fan off, not something I would want anyways.
With the 5 wire connection, the outdoor unit does have two stages, not clear if this is in heat and cooling but I'm assuming both. That isn't too bad but they don't describe how the stages work or how many BUTs each is. I would hope the lower stage is set to ramp. For example the Mitsubishi thermostat interface module in stage one ramps the setpoint slowly instead of running at a fixed setpoint. It also has a delayed off option in stage one which will keep the unit running once the setpoint is reached even if the thermostat input is off.
Make sure you got the hyper heat unit installed (ie 38MURAQ24AB3). The only difference between the two is one letter, so it easy to get the wrong one.
Thanks Akos. Yes they wired up 2 stages which the ecobee appears to be managing at the moment. I sometimes see it running at stage 2 and short cycling though which I don't like. I wonder if the 2 wire connection will be an improvement.
Yes I definitely got the hyper heat model, AB3. :)
Update.. I managed to contact Midea to ask about this as Carrier won't talk to homeowners and my dealer was brushing me off. Turns out you are absolutely corret Akos. The system will be more efficient and compressor speed will be more precise as the indoor unit will communicate based on its temp sensors to the outdoor unit. Next step is to get the dealer to change the wiring. Wish me luck. (Side note: so much for 'award winner' authorized carrier dealers... does not mean much in terms of their skills and knowledge, maybe it's just based on sales volume)
“Resistance heat during defrost. This is an energy pig”
I agree that the system will use less energy without the resistance but pig is a bit strong when I look at my numbers.
I have had 2756 defrost cycles at 3 minutes each= 8268 minutes of defrost = 137 hours of defrost. 137 hours x 36kW = 4960 kWh use in defrost so each defrost cycle used 1.8 kWh. The heat had to come from somewhere to defrost the coil if not from the resistance, then the heat pump must run longer to bring that heat indoors at a CPO of about 4 1.8 x.75 =1.35kWh saved per defrost is not a huge number in my mind. At $0.09 per kWh, you save $0.12 per defrost at the cost of longer defrost cycles with zero heat while the cycle is running.
My guess is my numbers are over stating the saving by 2/3. If I turned off 2 of the 3 hugely oversized resistance elements the defrost cycle time would remain unchanged.
Walta
You have 36kw of strip heat??? And 137 hours of defrost time? 4960 kWh is huge.
"You have 36kw of strip heat??? And 137 hours of defrost time? 4960 kWh is huge."
Yes I have 36kW of strip heat I understand it is way more than needed.
Why did I allow that much to be installed? Allowing the HVAC contractor to win on the size of the resistance cost nothing in operation costs and very little for installation and equipment but allowed the contractor to let me win by install what he felt was undersized heat pump. I see it as a win win choice.
137 hours of defrost across 5 full winters with 11,300 hours of heat mode run time does not seem out of line to me.
Walta
Hah hah, I think the previous poster may have thought you had 137 hours last winter alone (i.e., in 1 winter).
Yes, spread out over 5 winters does not seem bad at all.
~1000kWh per year just for defrost heat is pretty big. That is about one month of cold weather electricity use in a PGH for something that essentially makes zero comfort difference. The off time during defrost is much shorter than the gap between heat calls of the typical oversized furnace, loosing heat for those couple of minutes in the middle of the night simply does not matter.
~1000kWh per year just for defrost heat is pretty big. That is about one month of cold weather electricity use in a PGH for something that essentially makes zero comfort difference. The off time during defrost is much shorter than the gap between heat calls of the typical oversized furnace, loosing heat for those couple of minutes in the middle of the night simply does not matter.
I remember reading about an install where they had a hard time figuring out why the electricity use was much higher than predicted. It turned out that the system would always revert to strip heat during defrost, once disabled power use went significantly down.
Hi All, Just updating the thread now that the dealer has connected the indoor and outdoor units with the 2-wire communication link. I am not noticing differences but it's hard to tell as the switch happened during the shoulder season and now we're in heating mode. But it makes me feel better that my system is now wired optimally.
So far so good with the heating as we are hitting freezing temps. I turned off the breakers for the backup coils so I know that the heat pump alone is keeping our home warm! As the winter progresses I'll be curious at what temp I'll need backup heat, and what my cost of electricity ends up being.
It would have been nice to have a fully communicating system but at least the ecobee does have 2 heat pump stages and these are wired using Y1 and Y2 to the air handler. It's a bit of a mystery what the system actually does with these inputs though, as I have observed that the heat pump can ramp up to 2nd stage levels even when the thermostat is only asking for 1st stage. I suppose this is designed for cases when a single stage thermostat is used. Maybe Y2 just forces the higher power sooner.
The system does seem to be running quite a lot, I hope there is headroom for when the real winter arrives! I do have the backup coils but hoping they won't be needed except for the real cold snaps.
If anyone has recommendations on how to configure the ecobee in the best way in terms of thresholds, it would be greatly appreciated.