Heating a Large Home with Minisplits
I’m designing a pretty good house in central Utah for my family. It’s about 4500 sqft, so definitely large for this crowd, but not crazy. Main level plus full finished basement on a 60×40 footprint. We are fairly set on the layout to capture the views and support our lifestyle, but are still open to changes. I’m looking closer at HVAC now. We are building in zone 5B.
I designed with provisions for a traditional HVAC system with ducts in the conditioned space. Then I modeled the house in BEopt and have found that the main level gets up to temperature in the winter quickly when the sun comes out, then the heat doesn’t run for many hours. That’s a pretty normal winter day here. The basement stays uncomfortably cool when modeled with a single zone traditional heating system. About 62-64 degrees for 3 months.
Now I’m looking at zoning the levels separately which has naturally lead me to mini splits. I’ve run heat loss calcs on the house with 3 different tools and it consistently comes out to a heating load around 25000 BTU/h including the ventilation system losses. I’ve done a room by room estimate which I’ve labeled in the floor plan pictures. I’ve also labeled some potential head locations. I think it might be possible to use 2 of the Fujitsu ducted medium static pressure units for the whole house, but given the size of the house, and my limited understanding of duct design, that may not be feasible.
We tend to leave doors open, so air will have opportunity to mix naturally. I’m not opposed to electric spot heaters. The nursery off the master and the library in particular seem like good candidates. We are ok with some room to room temperature variation.
My thoughts on this are to have a head on the main level in the dining room over the office doors or under the dining room windows. Then in the basement family room and another head in the hall among the bedrooms. 3 heads would be a pretty straight forward install with no ducting. We plan to heat to 68F, but if we heated to 70 or 71 upstairs that would help with convective flow to the master suite and library.
I’m still searching for local professional help, but this kind of knowledge is a bit sparse in rural Utah. One guy wanted to install a 6 ton propane furnace… My biggest concern is that I need to keep this build moving and I’ll end up with a central system designed and end up with a low duct somewhere I don’t want it. Professional full design work has a delivery date about 12 weeks out currently, so I’m in a bit of a pickle here. I may end up biting the bullet and purchasing a license to Wrightsoft or Elite, but I’m not sure how well they handle mini split designs.
Thanks in advance for your thoughts.
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