MIDEA Ducted Minisplit / Heat-Pump Water Heater Location
Dear GBA,
I’m getting closer to the HVAC decisions. A Small Planet Supply sales person suggested a Midea 18k BTU ducted heat pump for my 868 square foot (but 10,000 cubic feet bc. high ceilings) house in the mild western side of Oregon, zone 4C. Several other HVAC installers quoted me for 24k systems with two interior heads, but I like the idea of putting a ducted unit in a central closet and then pushing air to the two main regions of the house.
a) The MIDEA (Advantage 18K Ducted) is a lot more affordable than a comparable Mitsubishi Unit (about half the price, installed). Is the Midea a reliable product? I have a question out to the installer about the # years warranty. What experiences have you had?
b) I had planned for a heat pump water heater to go into that same centrally located closet. To address the room size requirements of the 50 gal Rheem I was thinking of, I planned to leave the closet door off, for air flow (closet volume is about 240 cu. ft.). However I am learning that it is also not recommended that a heat pump water heater go inside a conditioned space, as the energy savings for water heating could be offset by increased need for heating.
My primary heat source will be a woodstove, located adjacent to the centrally located closet. However I don’t know as I age whether I will get lazy about keeping a fire going!
The house will primarily be for me, and my hot water usage will be a nightly shower at 2.5 gpmx15 minutes =37.5 gallons at most, plus dishwashing/sink use throughout the day. In addition to the concern about cold air being produced by the water heater, I am concerned about noise. The closet containing the unit will be adjacent to my bedroom. I considered putting the unit on vacation mode after my evening shower, and then turning it on in the morning when it would be less irritating. I read some posts here and people were saying that the Rheem 50 gallon was quiet.
*Since I’m on a well: ground water temp looks to be ~52 degrees here.
Will leaving the door off the closet address the air circulation needs? At my (somewhat low) level of hw water use, and with the concerns about cooling the conditioned/heated air, would I be better off simply getting an electric water heater?
I had been pretty sold on the heat pump hot water heater until I came across these concerns. I’m surprised that that HVAC installer who came out didn’t mention anything when I said I wanted it in an interior closet.
I look forward to hearing from you, and thanks in advance!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Have you looked at split system heat pump water heaters like the Sanden unit? The noise-producing components would all be outside, I imagine performance would be good in a mild climate like yours, and you'd remove all concerns with the water heater removing heat from the conditioned space. I think they're on the expensive side, but it might be worth looking into.
With wood as your primary heat, if you want to get really exotic (and expensive) there are systems that combine space and water heating using a hydronic woodstove and a storage tank -- but I don't think anyone distributed them in the US anymore so getting your hands on one might be near impossible.
Deleted
I have a heat pump hot water heater in my heated basement that has been running all year. In winter it does probably put a little bit of load on the heating system, but in summer it provides dehumidification. The key would be to direct the cool air from the fan away from where you might be. The Sanden unit looks interesting, but how many years will it take to pay off that price tag, particularly if installers gouge as much as some HVAC guys do on mini splits?
I understand your concern about noise, they do create fan noise. However, some units do allow for cowlings that may allow you to place it somewhere farther from your closet. This may help avoid cool air blowing on people as they walk by as you may be able to direct it away from a hallway....Also, your idea of switching modes may work.
Look online at the HVAC sites for install instructions and they will tell you what kind of clearances are required. I have an AO Smith and I believe their web site will show it.
Whether 18K is enough depends on what your heating and cooling loads are. In zone 4, guessing around 15F design temp, my guess is that even the 18K is oversized for 900sqft. The good thing is that a single 0ne-to-one install has much better modulation range (that 18K Midea should module down to 5000BTU, which is decent) so even if a bit oversized, it should not effect efficiency much.
I'll be installing probably the same unit soon (an 18K and a 12K), for the money you can't go wrong. They also OEM the mini splits for a lot of north American manufacturers.
For the water heater, get one that can be ducted, this way you can put a door on the unitilty room. Duct the outlet out of the closet and put a large grill on the door. Even if you are taking the heat from the mini split to heat the hot water, it is still about 2x as efficient as a resistance tank. I wouldn't worry about the HPWH using some of the space heat.
+1 on the heat pump still being better than resistance even with it "stealing" from the space heat. As Akos says, the total electric use for heating water, including that used by the space heating heat pump is only half of what you'd use in the resistance heater. And when you are heating with wood, you do even better, as well as doing much better in the summer.
I think it makes sense to put it on a timer to lock it out until morning.
Thanks Charlie for this analysis. With the utility rebate it is affordable to invest in the unit now, I can turn it off at night. I have had good sources advice against it because of the loudness.
Our Nyle Geyser RO HPWH steals heat from a conditioned space, but, for us, that heat is supplied by a ductless mini-split at as little as one-quarter the cost of fuel oil or electric resistance.
The Nyle is controlled by a smart plug that allows it to operate once a day between 02h30 and 05h30 when utility demand is typically low, and renewables often have a larger share of the overall generation mix (wind and hydro-electric in our case). Yesterday, with outdoor temperatures holding steady at 5°C, the incremental demand put on our mini-split was 0.32 kWh, as per its usage chart below. That hit will be higher during the dead of winter, but, as mentioned in an earlier post, for roughly six months of the year it provides us with "free" hot water to the extent that its operation offsets that of our dehumidifier, our home's single largest energy consumer during the off-season.
There are ducted heat-pump water heaters that allow you to distribute the cooled air more broadly. Would that help?
one installer suggested ducting to outside, which seems wise. Any concerns about this?
Hi Paula, I had originally considered that with mine, but the big concern with ducting a HPWH exhaust outside (and supplying from inside) is that it causes negative pressure on your house. That can have different consequences depending on the time of year and climate zone, but in most cases wouldn't be desirable.
oh wow, good point.
You could look at a high quality standard electric water heater as an alternative to a heat pump. Depending on how much hot water you will use, there may not be that much difference in overall energy use. I elected to install a Rheem Marathon instead of a HP water heater in my house due to space and noise considerations and there are only 2 occupants who do not use much hot water. My overall energy use is right at Passive House levels and I don't believe the HP heater would have given me much more improvement. Lower first costs, no noise, and likely lower maintenance.
Note that as we get better at making super insulated houses, the fraction of the energy use that goes to water heating gets bigger.
With your very low water usage needs, I'd consider a cheaper resistance water heater. And since you mention aging (in passing), you should know now that you will likely be a lighter sleeper as you get older. The quiet will be a big benefit of a simple electric version.
In the future when heat pump water heaters are more common, less expensive, and quieter, I will get one, but I got an electric to replace a noisy gas water heater (directly under my bedroom) last year and I'm pleased with the decision. My $0.02
You've given me lots to ponder on the hot water heater front. Thanks everyone for the input. A simpler system always appeals, and I could switch to heat pump later as Andrew C suggested. I am getting mixed signals about whether the heat pump heater in the closet can work or is ill advised...even if vented. Anyway...back to the Midea ducted heat unit. I had an installer bid me a good price for the 18k unit, about half of what another installer would charge for installing the Mitsubishi unit. The Mitsubishi has a 10 or 12 year warranty, and Midea is only 7 years, but I guess if I am primarily relying on wood heat and this is a backup, maybe that is ok.
I had even considered a DIY heat pump like this one
https://iwae.com/shop/24k-btu-17-seer-mrcool-advantage-ductless-heat-pump-split-system-3rd-generation-wall-mounted-ha18430.html
for even a lower cost, but a part of me likes the idea of concealing the heat units rather than having the head (or heads) visible to the living space. Plus I can size down with one unit in a closet vs. two heads.
So I guess I'm just hoping that the Midea is a reliable choice, if not quite as high end as the Mitsubishi. Also, is Midea common enough that it could be serviced by a local HVAC professional if needed? I don't want to buy something obscure.
Thanks, all.
Hi Paula,
In regards to your question about Midea being common, my understanding is that they’re one of the largest global manufacturers and that many minisplits in the US are just rebranded Mideas. Carrier, I believe, is one such example.
Correct. My Midea came in a Carrier Midea North America box from Georgia. It had both Carrier and Midea stickers in the box. Midea makes the majority of the brands out there. Even some of the Diakin and Fujitsu units appear to be rebadged Mideas.
I have had 2 Midea 12k Premier hyper heats I self installed running basically nonstop for 2 years with zero issues. I saved close to 10k over what 2 Mitsubishi's would have cost to have professionally installed. I could still replace both units 6 times and would still be ahead. They each cost me a little over 1k each.
The warranties are sort of useless in my opinion. In most of the world these are disposable appliances. Mitsubishi may give you a 10 or 12 year parts warranty but that doesn't include labor. 5 years in and you have a bad compressor you are going to pay a fortune in labor to replace it. I have heard that many times they recommend an entire outdoor unit as it often cheaper. If my Midea outdoor units has a leak or major problem I would just replace the whole outside condenser for like $600.
One person suggested that the Mitsubishi might be quieter than the Midea. I guess that might be a way that paying more yields an advantage. Thanks for the points you bring up here.
Agree with others that you should consider noise for the HPHW particularly the resonance from the compressor. If it's in a closet you could sound proof it but obviously it would need venting. The Rheem manual specifies how much space/venting is needed for closet placement. Obviously there are a lot of people putting these in closets since that's where the old HW heater was placed.
The HPHW may give you more options than the standard electric resistance. For example, you can schedule when the compressor turns on so perhaps you could schedule it when you are out of the house or if you can't hear it from your bed room then schedule it at night. Additionally, the unit from Rheem is hybrid, thus it can heat with HP and/or/combo electric resistance and this can be changed with an app. Thus you would have the option of heating water with electric if you didn't want to hear the compressor at a certain time. Again, you obtain the benefit of dehumidification when the HP is running.
I'll toss out that I'm looking at providing space heating and water heating using an indirect hot water tank with an electric heating element. The "indirect" part is the heat exchanger coils- rather than heating the water tank via this coil (from something like solar or a boiler) I will pull heat out for my space heating (panel radiators).
I don't require a lot of heating capabilities (current design est. about 16.7k BTU). And water heating requirements aren't all that high. I was almost set on utilizing an electric boiler and an indirect tank to handle all of my needs until someone asked me to consider just the indirect tank (w/electric heating element).
I've found ONE tank that has a 6kw heating element: and it comes in a gigantic tank- 80 gallons. Most seem to have 3.5kw elements (and are smaller tanks). You'd need about 4.5kw.
A pump or two (small, quiet and energy efficient), PEX piping, some valves and a couple of sensors. Not a easy DIY, but doable. No complicated stuff here at all. Costs, depending on labor, might even be less than any other solution.
Be sure to select a wood stove with a BTU output that's close to what you actually need. It's easy to overpower with a wood stove.
Your heating/water solution sounds clever. I think it's beyond my DIY capabilities, but if it works out you should share about it!
I did make sure that the BTUs estimated by HVAC people matched the BTU's recommended by woodstove people and my stove is right in that range (MORSO 7110). Chimney will be installed soon but no insulation in yet to really get a sense of how well it's heating.
I'm hoping to install the heating system before summer, when I'll be focusing on siding, if I can pull the hvac money together. I guess installing heating system after siding might also be an option, although i feel like detailing penetrations is more well-done before siding.
Paula, that Morso is rated up to 45,000 BTUs (maximum heating space about 1,300 ft-sq). This is similar to what I'm running in an semi-efficient 1,3500 ft-sq house; I can readily heat my house (40 degree delta is fairly easy to hit!). I would NOT use this same stove in my future build (even though the floor space will be about 40% greater). I'm considering the 6140, though that too is a little on the heavy side as BTU output goes: I'd likely have to open windows up.
Did you mean 13,500 or 1350 square feet for the current house?
The Morso page says up to 45,000 BTUs but the manual says this: "Under specific test conditions this heater has been shown to deliver heat at rates ranging
from 11,000 to 25,000 Btu´s." The HVAC folks looked at my plans and estimated I'd need 18k-24k BTUs to heat the house, so it seemed like a match, and the wood stove sales person agreed. I hope this is correct!
You might want to read this article: "Where Does the Heat Pump Water Heater Go?".
Thanks, that article was very helpful.
Hello, great question! Great answers as well…my question since this was a while ago, have you started or finished the envelope of your house?
I think this us more important then anything else your working on… that said, its more important of what you do on the outside then even insulation and heating?
Note: investing in a Sanden, although more $$$, is far better for the planet then all other heat pumps considered!
Please let me know? Thanks