With the energy efficiency measures we are taking: air sealing, more insulation, triple-pane windows, etc, we know that the HVAC (heating ventilation air condition) requirement will be much lower than most houses in the neighborhood. Normally a detailed calculation using the ACCA Manual J (Heating and Cooling requirement calculation) and Manual D (duct size calculation) guidelines with commercial software tools will give good answers.
Dave Robinson, however, has developed a simple spread sheet that does a quick Manual J calculation. For houses between 1500 to 2000 sq ft, his spread sheet usually comes to within 10% of the full calculation. We don’t need to use Manual D as we are not planning to use ducts that are outside of the conditioned space. We still expect our HVAC contractor to run the full Manual J calculation to validate our results.
Dave’s calculation shows that the heating load is about 25,500 BTU and the cooling load is 23,500 BTU. This means that we will only need a small HVAC system to provide comfort for this house.
Some of the key input to Dave’s calculation about this house are:
- Room temperature to be maintained at 70 deg F in winter, 75 deg F in summer
- Designed winter outside temperature is 0 deg F, summer outside temperature is 85 deg F
- Best air infiltration at .3 ACH (air change per hour) in winter, .2 in summer
- Attic insulation at R-60 (see Insulation Material for an explanation of R-value)
- Ceiling insulation at R-19
- Wall insulation at R-19
- Floor insulation at R-11
- Triple pane windows at R-5.5
Coming next: HVAC Equipment Selection
See also: Partnering With Green Hearted Companies and the entire From Foreclosure To Green Home series.
