Help me on HVAC proposal and calculations
Hello, first post here; long time reader.
So we are renovating our new home in East TN and are working on HVAC proposals. We have very few qualified contractors in this area from what I hear. I need some opinions on what I was presented.
The house currently has two A/C units and two furnaces...one system for 1500sqft downstairs/1000sqft basement and one system for 1500 sqft upstairs.
Dehumidification is important to us especially in the basement so I definitely want a dual stage compressor unit for that area. He recommended single stage for the upstairs.
The contractor in question had apparently worked on this house for years before we bought it so rather than do a Manual J calculation, he just sized it based on what was there because he "knows this house". Here is what he proposed:
All York equipment
2 ton 16 SEER single stage condenser
95% AFUE 60K BTU/hr single stage furnace
3 ton 18 SEER two stage condenser
98% AFUE 80K BTU/hr modulating furnace
I was concerned that we might be oversized so I did my own calculation with HVAC-Calc and got these numbers:
Basement Heat Gain 7,175
Basement Heat Loss 13,152
First Floor Heat Gain 27,164
First Floor Heat Loss 46,434
Second Floor Heat Gain 14,373
Second Floor Heat Loss 24,498
Total House Heat Gain 48,713
Total House Heat Loss 84,086
The contractor has spec'd 3 tons main floor/basement of cooling with the main floor/basement dual stage and 2 tons for upstairs. This seems pretty reasonable, yes?
Now the furnace is where I see a problem...he has spec'd 80K BTH/hr for main floor/basement and 60K for upstairs. Looks like it should be 40K BTU/hr for upstairs. But on the main floor/basement, total heat loss from these calcs is right about 60K BTU/hr. Should I go with a 60K in this case or is 80K modulating OK? Seems like 60K might be pushing it on really cold days. Plus I assumed R-13 for the walls but it may be R-11...hard to say.
Thanks SO much for your input.