Sizing a Hyper Heat Minisplit System
My goal is to be as green as possible, save money in the long run, and get as close to $0.00 utlities as possible. It seems like mini splits and solar would help me get there. I’m just not quite sure how or if it is realistic in Southern New England
I recently got a quote for $23,000ish for a 48k hyper heat multi head mitsubishi unit. This includes upgrading to 200 amp service, a 12k gl head in the living room (215 sq ft) that will hopefully also heat the dining room through open 4 foot wide doorway (130 sq ft) A 9k ceiling casette in the kitchen (126 ft) the kitchen is across from the dining room down a 9 foot long skinny hallway. I am hoping that some of this heat would reach down hallway and the bathroom (30 sq ft) that is about halfway down the hall, and maybe a little bit rising up the staircase off of the kitchen. On the other side of the long hallway is a bedroom (140 sq ft) and it is including a 6k gl unit in there. Upstairs there would be two units. They are suggesting a 9k in the master (150 sq ft) with bathroom (50 sq feet) off the side, and an additional 6k unit in a small bedroom (100 sq feet)
The quote includes two 3 port branch boxes. One would be left open to allow future expansion of adding an additional unit in the basement. We hope to finish about 500 sq feet of space down there. According to the contractor our total btu of the units could exceed the 48k condensor. I think he said it can operate at 130%?, which means we could add a 12k or 15k head in there in the future. Part of me is wondering if I should ask for the 3 port and the 5 port in case we want to put two smaller zones in the basement
Is this quote high?
Is it capable of heating and cooling my whole home in this configuration?
Our home is older (1945), but national grid had rise come out and install about $3000 worth of additional insulation in the attic, and kneewall storage areas. They said the basement and exterior walls had obviously already been updated by a prior owner. I am hoping this means that our home is well insulated. Last year, prior to adding insulation we used maybe 800 gallons of oil to heat our home and provide hot water for the entire year. We barely turn on the heat upstairs and leave it about 50 most of the time. Downstairs when we were home we would turn up to 65-68 and then use a nest to turn down to 55 while sleeping or at work. Although due to the pandemic, we were home significantly more than normal, and I spent some of my work hours at home.
Would this unit gobble up a ton of KWH in the winter? I have read that they don’t always modulate as well as one might hope. Unfortunately because my home doesn’t have an open floor plan I’m not sure we can really go with less heads. At about 23 cents a KWH in our area I want to make sure this makes sense. I would love to know how many KWH real people use to heat their home with a similar system in New England.
Would we be better off with two smaller Multi Units?
Are the gl heads fine, or would others modulate better?
If anybody reads this whole thing and provides some advice, I offer you my tremendous thanks.
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Replies
What is the total square footage for your house, not including the basement?
A 48k Unit seems gigantic, and the fact you mention it's a GL head doesn't sound good.
Hi, Eventful. Thanks for responding. The total sq footage is 1300. What issues exist with that type of head? Does Mitsubishi have one that performs better?
Hi Jalem, Thanks for the info and the layout pdf.
I have a 1,100 sqft single level 1955 ranch, In the Hudson valley of NY (Ellenville, NY specifically) so we have a nearly similar climate zones.
I have a two single units, 12k BTU Mitsubishi FH12 and a a 9K BTU FH09. These have been replaced by the FS series. These carry 100% of my heating load with ease (temps set to 71 - 24/7). In 2018 we had the 2nd and 3rd coldest low temps, -12 and -13 , on record and had no issues. In the summer I just run the 12k unit during the day and the 9k down in the bedrooms end of the house at night. The total came to $5000 after rebates
I have an all electric house, all appliances and hot water (Rheem Heatpump water heater) and run everything on a 100amp service. With an energy meter I have never seen anything over a 60amp draw at anytime (even that was a rare occurrence of both mini splits defrosting at the same time, running our electric range and the fridge cycling on).
At 21K BTU I'm just oversized for my own house for heating load, at 48K BTU for 1,300 sqft on your own it's grossly oversized even accounting for adding in the basement.
I would think a 24-30k BTU MiniDucted system would suit you well if factoring in the basement load. Like others have said due to your home having many partitioning walls a Ductless system may not be the best option.
Evantful, is your condenser the Hyper heat model? I see you use a single 9k to heat more than 1 room. Do you leave the doors open? Do you have some sort of room to room vent?
Unless your home has giant holes in it a 15 or 18k unit should be enough to heat your entire house. The question is distribution. A ducted unit would be best, but one or two ductless units might work. Can you supply a floor plan? Is Ac important? What do you use for heat today?
Thanks for the response. We currently use oil heat. I'm estimating we used about 800 gallons of oil for heat and hot water last year. A/C is important. I will attach an image with a rough layout of our floorplan
I don’t think your home is a good candidate for ductless mini splits. I would definitely look at ducted units. Dropping a hallway ceiling or running some soffits to get one register per room would be best. Fujitsu and Carrier have ducted mini splits that can be installed vertically with a central return which will help minimize closet space needed. Search around this site for similar threads. I will try to markup your floor plan tomorrow with some suggestions (or maybe Akos or others will beat me to it). What is your ceiling height on each floor?
On the first floor it is the standard 8 ft, the second floor is only 7 feet tall as it is an older home.
Your house is too small for a ductless head in every room you want heated. You should do, or get done, a room by room load calculation ("manual J") but in the meantime your general options are:
1. A few minisplit heads in central locations. The heat won't distribute very well, to the other rooms, but you seem like you have been fine with that kind of scenario in the past so it might work for you.
2. A few ducted minisplit heads in strategic locations to allow ducts a few feet long to connect to adjacent rooms. For example, I'm looking at the ceiling of the downstairs hallway and thinking you can reach from there to the living room, dining room, bedroom 1 and the master bedroom. And you have height there.
3. If you want a heat source in every room, another way to go is an air-to-water heat pump, with a panel radiator in every room except a few spots where you use a slim wall-mount fan coil unit that is a lot like a minisplit head. Panel radiators are inexpensive, come in ratings as small as you need for a tiny room, and are visually less obtrusive. This is a great solution, but it's hard to find installers who are skilled in installing those systems, so it's usually more trouble than it's worth.
Interesting. Thanks, I hadn't heard about the water heat pump. I will do a little research. I think I am going to try to get some quotes for adding ducts, as it sounds like that would be the most efficient way to go.
If you can get by with a smaller unit, that 200A service upgrade may be unnecassary, which would save you some money. Even with a 100A service, that 48k hyperheat unit would probably be OK, but it depends on what your other loads are -- the hyperheat unit is going to be a big addition in terms of electrical load.
When I looked up some basic specs (I'm not sure it's exactly the model you're looking at, but it should be close), the max load is shown as 5kw. That means 5kw/h of electrical use for every hour the unit is operating in heating mode. That's about $1.15/hr to operate the unit using your 23 cents/kwh electric rate (which is pretty high, BTW).
I think you'll have a hard time zeroing out your electric bill with solar here, and it certainly won't be cheap to do so. I like using solar for "peak shave" myself, which means I count on it to help with heavy load during the day. This avoids any need for batties, and peak shave works regardless of what kind of net metering rules you may have in your area. Peak shave works best in the summer though, since the time of max output from the solar system is usually pretty close to the time when your air conditioning is running the most. In the winter, with cloudy days and less hours of sunlight in general, you'll get much less output from your solar system, which makes it more difficult for solar to offset your heating needs.
I just think about solar to offset cooling load. Solar DOES still help you in the winter with heating load, just not as much. If you run your payoff calculations based on the more predictable air conditioning numbers, anything extra in the winter becomes something of a free bonus.
Bill
I would run through the calculations here to see:
https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new
This will get you into the ballpark in terms of overall heating load, we can work from there to suggest a better layout.
Generally, it is a bad idea to install an oversized multisplit especially with small heads on it. These are a recipe for low efficiency, high running cost and can create comfort issues.
Most likely you won't need a service upgrade for a properly sized heat pump. You might need a service upgrade, or at least a panel upgrade to a solar ready one might be needed if you want to get a larger PV array .
For net metered setup, a standard 200A panel will limit you to a 7.6kW array max, a 100A panel with 100A busbar rating would be 3.8kW max.
We definitely need a panel upgrade for the system, but once we add the solar too, we will need the 200 Amp to get the larger array on net metered. Since they needed to do the panel upgrade, it seemed like I might as well have the electrician take care of both at the same time.
I will do the calculation and see what I come up with. Thanks for sharing.
Rereading your original post I see you have a basement. Hopefully you can run ductwork there for the main floor. Upstairs I would see if you can steal some of the gray closet to put a ducted unit with very short runs to each bedroom. The units can be installed vertically in a very small space like shown here https://www.greenbuildingadvisor.com/article/getting-the-right-minisplit
Interesting. I am going to reach out to contractors about ducted units. I am worried the cost for that will be quite a bit higher, but we will see. I also have kneewall storage going along the small bedroom and it connects behind the closet of the master. I wonder if that would be an easy spot to put in ductwork.
You should save enough on equipment to cover the cost of some simple ducting. I would expect it to be cost neutral, but much better performance.
The first contractor kind of balked at the idea of doing ducts. I have another one coming out on Thursday, we'll see how it goes. I also started reading about room to room air vents. I'm wondering if that might be an ideal situation upstairs between the two bedrooms. Or even between the living room and the downstairs bedroom. (there is actually a vent between the living room and bedroom already, although no fan is installed, we have always found it kind of odd) Maybe I could get away with two single zone compressors. Like a 15 or 18k in the living room with an air vent, and a 9k upstairs with an air vent.
The problem with room to room air vents is that blowing 72 F air into a 68 F room doesn’t really transfer a lot of heat. If I were you I would keep looking for a contractor. Maybe start looking at Carrier contractors, that’s where i had the best luck actually getting a bid.
My local utility works very hard to make to not allow net metering with solar installation large enough to cover more than 80% of you usage and I would be surprised if yours was much different.
Consider getting bids for several single head systems. Single heads you better performance in that they can run a lower speeds than the multi head unit. Single heads give you more flexibility to turn off parts of the system if it happens as seems likely your system is grossly over sized. Single head unit also give you redundancy so when some part fails as something will sooner or later you will still have some heat but a multi head system would likely leave you dead in the water. Yes it will cost more but likely not much more.
Before they insulated did you get a blower door test? If not a blower door test before and after air sealing could make a huge difference in your homes comfort level.
Have you done Dana’s heat load calculations with your oil usage and local weather data? This will give you a very accurate sizing for your system.
Walta
Thanks for your feedback. It appears that the electric company will allow us to go to 110%. I am trying to get this done first to bring my usage up, as I was unaware that they wouldn't allow me to get the size system I wanted. I hate that they have such control, but it sounds like some companies are even worse.
I will ask about single head systems. They did do a blower door test before they did the insulation work.
I haven't done the heat load calculation. I see someone posted the link above so I will give that a shot.
Fellow Rhode Islander here who recently installed solar here. At the moment our utility, National Grid, is not terrible to work with for residential solar installs.
Net metering is currently on a rolling annual basis, with no time of use provisions - so pretty good still, but could change down the line. They will allow line side taps to avoid the busbar limits, so you may or may not need a panel upgrade, depending on the size of your array. I do believe they will allow an adjustment to your historic electricity use for system sizing, based on a prospective piece of equipment (like a new heat pump). But I didn't do that, so don't bank on my word.
Whether the solar array can cover your electric use 100% or not is irrelevant in my view. With our really high electricity rates ($0.20-$0.22/kWhr!), solar pencils out easily, whether it is covering part or all of your use.
I figured a 30 year all in electricity rate of $0.08/kWhr for our system, using $3.25/Watt system total cost, less the $0.80/Watt Renewable Energy Fund grant and the Federal Tax Credit on top of that. Financing it with a solar lender would have added maybe $0.01-$0.02/kWhr. I also figured we were breaking even in about 7 years.
Paying $0.08/kWhr vs $0.22kWhr (and always rising) looks pretty good, even if it is only for half your electricity use.
Reach out to a local solar installer to get better details for your home. If they claim the REF grant doesn't exist, call someone else. That means they don't like doing the cumbersome paperwork. Others will.
Good luck!
When I ran numbers for a small (3kw) system here, on my time of day rate and an on-peak kwh rate somewhat close to yours, my payoff was less than 5 years -- and that's only allowing for peak shave (no net metering), and only in the summer -- so winter is like a free bonus. The short of this is that solar makes sense with a reasonable payback even if you don't have net metering options.
Bill
This link is to the 15 minute calculation that will give you a very accurate number for an existing building with fuel use records.
https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new
Be sure you understand your local net metering agreement and its finer points knowing it is not set in stone and could be changed in the future. In my local agreement if you somehow manage to fool them and install enough panels to produce more power than you use over the course of a year the utility will buy your excess at the wholesale price about 10% of the price they charge you.
What the ACH50 number from your blower door test.
Seem like if they did not test while sealing they are guessing at where to seal and if they do not test after sealing they do not care to know if they did a good job or not.
Walta
They did test before sealing, although they did not do a blower test after. I wish I had seen this site back then! I will have to look and see if I can find the before data, I'm not sure what numbers came out of it.
So I found the blower door tests before they did the insulation and air sealing work. I'm not entirely sure how to read this info, or really how useful it is since it was before the work was done. I'm quite curious to know what it would be now.
TOTAL VOLUME 9960 CU.FT.
Finished areas suitable for year-round use.
IS BASEMENT INCLUDED IN VOLUME? NO
OCCUPANTS 2
BEDROOMS 3
BLOWER DOOR # 3490 CFM50
BUILDING AIRFLOW STANDARD (BAS) 899 CFM50
70% BAS 629 CFM50
If blower door # is below 70% BAS refer to ASHRAE 62.2-2016
EXISTING AIR CHANGES PER HOUR 1.40 ACH
Assume an average 62.5 CFM reduction per hour of air sealing.
When I calculate your ACH50 number using their data I get 21 ACH50 this is an abysmally bad number but about what I would expect for 1945 1.5 story building.
ACH50 is calculated by multiplying CFM50 by 60 to get air flow per hour, and dividing the result by the volume of the building.
(3490x 60) / 9960= 21
ACH50 tells us how many times per hour the entire volume of air in the building is replaced when the building envelope is subjected to a 50 Pascal pressure.
Knowing the current score would be informative.
“EXISTING AIR CHANGES PER HOUR 1.40 ACH
Assume an average 62.5 CFM reduction per hour of air sealing.”
This line from the report seems to be magical thinking that air sealing would reduce the air leakage by 93%. My guess is if they tested afterword their dreams would be crushed.
My guess is they reduced to flow by 25% assuming they spent less than 20 man hours air sealing.
The good news is you can save lots of money by plugging the leaks the bad news is it is dirty nasty hard work requiring little skill.
Walta
Thanks for sharing the formula for the air blower. I also attempted to use the formula to calculate my heat load based on fuel consumption.
I come up with a range of 18k- 20k btus. My calculation isn't the most accurate as I don't have very good measurements of oil consumption. I buy 150 gallons of oil at a time, but it doesn't necessarily fill my tank, so I approximated.
We currently keep the house pretty cool to save money and probably wouldn't mind having it slightly warmer. I'm thinking that 20 btu's with the insulation upgrades we recently did would probably get us to warmer than we were last year throughout the house. I can't believe the contractor was recommending a 48k multi system now.
Although it sounds like the ideal system would be to have some vents, and I will see what the next contractor says, I am currently leaning towards getting a 12k system for the living room and a 9k system for upstairs and seeing how well I can get the heat to distribute. I don't mind leaving doors open. I can continue to work on air sealing. If the living room is 72 and the kitchen is only 65 I don't think we would be terribly upset by that scenario. Now if the kitchen was only like 50 and the living room is 72 that might be more problematic but for now we still have the oil tank for back up if need be. I'm still not entirely sold on a system. So many people say two singles are better than a multi system. If I look at singles it seems that the Gree Sapphire has the best Hspf around, but then so many people say Mitsubishi is the best. I'm pretty sure if I try to downsize to a 20k system the contractor is still trying to convince me to get the a multi mitsubishi Mxz 2c20. If it's more accurately sized, then maybe a multi isn't quite so bad. I had no idea figuring out which system to go with would be so complicated.