1 large or 2 smaller heat pump head units for semi open floorplan
Greetings, have read many posts and am thankful for all of the helpful info regarding, mostly, heat pumps.
Am looking to install a split system in my parents’ 2 story home, ~710 sq ft per floor, 8 ft ceilings, full basement. The upstairs design is settled in terms of head units and size but am wondering about the ground/1st floor as 1 person mentioned that 1 larger unit might not circulate the air well enough. Another had 1 larger unit. Both are pseudo competent(which is high for the area) and I am unsure of how the units function in reality. If it is close, 1 is much easier to do large wall unit but if it is going to perform significantly worse then will do 2.
This is mostly for cooling as there is hydronic baseboard heating. Not sure which will be cheaper/better to run for heating. Attaching a literal back of the envelope sketch of the floorplan.
Have done manual J(mine around 25k heating, 1 contractor was around 27k but maybe with a high design temp. This was for both floors so about 12-15k BTU for ground floor) and such but any additional feedback on sizing is welcome. This is in a 5A climate, capital region of NY. Blower door test ~4.6(which is, apparently, miraculously tight for the area).
Basically, there are, mostly, 4 ft cutouts between 4 sections, 1 head unit will be placed in dining room(bottom right corner) and hoping that will blow enough air to living room(which is not used in practice but want it cooling for future buyer). I know some models swing air. The foyer and such doesn’t need to be as cold but would like the living room to be cooled close to the dining/kitchen level.
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My vote is 2 smaller units.
You say you came up with 25mbh for heating but what about for cooling if that is what you will primarily be using these for?
I don't think you'll get the proper air distribution with just one unit. If you put both units on the 26ft (south?) wall where the heat pump is and have them blow north they might distribute the air the whole length of the house. You would need (2) 12k units in that case I'd assume.
Thanks for the reply and sorry for my poor writing. Ground floor is 12-15k btu(have edited original post to state total for whole house and 1 floor) for heating. Cooling btu was about 60% of heating, I think.
Will probably need 'full load' heating btu for the house for rebate programs, I believe.
Was wondering if one 15k unit that blows air forward and then to the side in the cutout to the living room from the dining room would work. I assume the air is not blown in one direction from most heads. The person who first mentioned 2 units thought 1 unit would have to be blow very strongly and it would be too noisy and maybe unpleasant to get the air around decently.
2 units will definitely get enough air around. 1 is much easier due to only southern wall be practical and furniture making that impractical in the living room.
2 would be maybe a 7k or 6k and a 9k. Possibly two 9s though that is a bit oversized.
1 would probably be a 15k.
35BTU/sqft in zone 5 with a house that tight is simply not possible. I would rerun your heat loss calc on something like bellow. Make sure to use your actual blower door numbers for air leakage.
https://betterbuiltnw.com/hvac-sizing-tool
If those are 2x4 stud walls with batts, you should be around 10-15 btu/sqft.
As for heating, unless there is a good reason not to, always go for a ducted minisplit. If you can't go ducted, multiple one to one minisplits can work, they are just more maintaince down the road.
As mentioned to @krackadile the whole house is 25k+ btu for heating so the floor in question is about half(2nd floor is much worse for cooling).
I did my own manual J using the site you referenced some time ago. That was 24k heating but I used a 0F design temp and ASHRAE has -5F which is definitely too low.
Walls are 2x6, I assume batts but definitely has spots of low or no insulation.
I don't think I used the blower door test number for air leakage, I just guessed and was conservative. I don't think much of the construction of the house.
I do remember changing 2x4 to 2x6 walls and it dropped it around 25%.
Perhaps I will run another if I can figure out where to input the blower door # conversion.
No ducts and they are, essentially, impossible. Another issue of having 4 total heads and 1:1 is 4 condensers. Most contractors want to super oversize and run a huge multi which is never happening. I might be amenable to 2:1 with 2 condensers. Almost want to install it, myself, and have someone do the electrical.
Besides the general design what do you think about 1 vs 2 heads on the ground floor now that I've corrected my erroneous info?
I've read many of your posts, previously, and they were a shortcut to knowing enough not to let installers decide on what gets done so thanks for that.
How about one ducted split?
Installed about where the number '3' is would allow very short duct runs to all the spaces.
If you have a basement, why not put a ducted unit there? You can do a very simple home run to underneath the windows of each room.
For the 2nd floor, you can do a single wallmount in the hallway to get you cooling and bulk of the heat with resistance baseboards for the bedrooms when doors are closed.
This will give you the option ducting from the basement up to these rooms down the road if doing a reno or if you are looking for slightly more efficiency.
This will get you the house conditioned with only two zones, about the only drawback is for cooling in the summer you'll have to leave bedroom doors open.
Ducted are not possible for a great multitude of reasons. Nobody in the area installs them as one. Or almost nobody after going through dozens.
Top floor will have 6k or 7k in each of 2 rooms, other room + hallway empty. This will bleed into rest of floor, anyway.
Looking at some specs for air throwing distance they seem quite far. If 1 wall unit in the dining room oscillates the air from blowing toward kitchen and living room it might work.
Could always add a second in the future. Really do not want to deal with it now due to my mother and her furniture. If a contractor requires it for a free/almost free system with state programs then it is more palatable.
Based on my Manual J of 14k cooling for BOTH floors does a single 12k wall unit seem sufficient for the floor nevermind the wall obstruction? That seems very obvious but even the conservative installer who seemed OK(but is now out due to shenanigans with the NY program) was going to put a single 15k unit there. Mitsubishi H2I 15. And 2 6k of the same in each bedroom upstairs. All 1:1. Not sure if the single wall unit was his preference or due to the blockage of the wall in the living room. I forget.
With a chopped up place like that a single unit won't be enough for heat on the main floor. You might be able to get away with 2, one on each of the 13' sections of south wall blowing up in the sketch.
Duct work is not that hard. My brother-in law vent through something similar, dropped by a morning, showed him how to do it and he ducted up his whole house with hard pipe. Saved a bundle in the process.
Once you have the ducting in place, HVAC installers are now just installing the indoor unit which they are usued to as it is their bread and butter when swapping out failed units.
The other option is to ask for a ducted furnace. This is again standard install for them, you can get a budget furnace with an ECM air handler but instead of AC install a proper cold climate heat pump coil (ie Mitsubishi Intelliheat or Carrier high heat 38MURA).
Duct work is out. Doesn't want large holes in floor for vents. Air handler would be in basement room that is in continuous use. Not sure if that is another barrier. So you can see that is not an option.
Still will have hydronic baseboard gas heat so not too concerned about that on main floor if it is not full on.
If it cools the space down to 75-77 that is far better than the current situation.
Since all of the installers in the area want crazy money for a day of work might just go for 1 large cheaper brand unit.
Mitsubishi, etc. have no warranty without their installer so the equipment is then not worth the price.
The most accurate way to sizes your equipment is based on historic fuel usage and weather data not manual J.
https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler
Avoid systems with mutable heads connected to an outdoor unit.
If your local installers don’t do ductwork it is because you are talking to the wrong contractors. Sound like lazy hacks to my ear if you let them do the work you will be unhappy.
If you are going with a single unit, it would be silly to stick it in the far corner and expect good results.
Consider the MrCool DIY units.
HVAC warranties are over rated. Almost never is a compressor parts claim paid and the labor coverage is very short. The best you can expect is the part is no charge but somehow it cost $350 labor to do the 15 minutes work to change the part.
Walta
I installed one of those MRCool DIY Units and it worked very well and was a pretty easy install.