HVAC & home systems
By using our calculators, you agree to our Terms of Use.
Heating and cooling planning math — not Manual J, not code compliance: estimate cooling BTU/h from floor area, sum insulation R-values and U-factor, size ventilation CFM from air changes per hour, and find round duct diameter from CFM and velocity. Cite DOE/Energy Star style rules of thumb; confirm with licensed HVAC design for equipment selection.
4 tools in this section
BTU
Estimate cooling BTU/h from room area using a rule-of-thumb factor. Not a Manual J load calculation.
R-Value
Sum insulation R-values in layers and find U-factor (1/R). Free building envelope estimate.
CFM
Estimate required CFM from room volume and air changes per hour (ACH). Ventilation rule-of-thumb.
Duct Size
Estimate round duct diameter from CFM and air velocity. Simple HVAC duct sizing estimate.