Calculating Heat Load for Small Home
I am new to here and I am overwhelmed by the information there. This is such a good website!
Long story short, I am a first time homeowner on Cape Cod, MA (Zone 5) with a ~1500 sqft 2 stories house. I recently want to install a mini-split ductless heat pump because my current electric baseboard heating just give me CRAZY bill (I have been getting ~800 dollar/month for three months now).
I have reached out to three HVAC companies, they quoted me different machines but their outdoor units are ~36000 btu to 42000 btu range. Yet when I try to do Manual J calculation (which I admit is more complicated than I thought), it only gives me about ~20000 btu for heating. I am bombed by the difference here and I don’t know what to trust… So my questions are:
1. On ballpark, what is the rough estimate of heating BTU for my house? I have a finished basement with no heat source. Just finished Mass Save recommended insulation which blows R38 up to 12 inch in the attic with R60 rigid board and install 2 inch knee wall board as well. Blow Door Values at CFM50 is 1770 (previous 1920, said that 1770 is the lowest that they can go). THE PROBLEM is that I don’t know the insulation material in the sidings since previous homeowner didn’t tell me, but this is a 1980ish Cape…
2. I noticed that some people say if the system is oversized, the energy bill will go up with short cycling and all that stuff, but some others may say since the current system has variable speed motor, the oversize issue will not be that much. I am wondering that whether this claim is true?
3. A Mitsubishi specific question…one company quote me a MXZ-SM42 series and the another quote a MXZ-5C42 series. Both with H2I tech but it seems that SM is the newer generation? I am wondering that anyone knows the difference of the two?
Thank you so much!
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