Minisplit Performance After Insulation and Air Sealing – Too Hot
Our 1800’s farmhouse is heated exclusively by a 48K BTU Mitsubishi H2i. When I installed it, the house was drafty as all heck and had almost zero insulation. It worked pretty well.
But now, everything has been meticulously air sealed and the walls and ceiling are insulated (R-25 Walls & R-60 attic). The 12K air handler in the main area upstairs that was just bordering chilly this time of year before is now swelteringly hot. No matter how low the thermostat is set, the MHK2 in our master reads 77-78 degrees.
Can I remove it from the system entirely and just use the remaining 36k BTU? Even with the head unit turned off, it’s still hot. Yay insulation, but it came with side effects!
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As long as you have at least 2 heads connected, with those you can go down to something around 25% of rated capacity of the unit, there is absolutely no problem in going down to 36k of heads.
I don't know how your place is set up but the 2nd floor air handler usually does the bulk of the cooling in most houses, so make sure there is sill cooling capacity up there. Next to impossible to cool a multi story structure with a main floor unit even if well sealed/insulated.
Good deal. Any idea how this effects efficiency? This unit is used primarily for heating and I’ve read mixed reviews on whether an oversized outdoor unit is beneficial or detrimental.
If you look at here:
https://ashp.neep.org/#!/product/31982
The COP of the unit is going up with lower load. You'll probably gain a bit of efficiency provided the remaining indoor head have good runtime and not cycling too much.