Heating & Cooling calculators
Size air conditioners and heating loads for a room by area, sun exposure, and occupancy.
Heating & Cooling
Attic Ventilation Calculator
Calculate attic ventilation with the 1/300 rule. Enter attic square footage and vent net free area to size the intake and exhaust vents your roof needs.
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BTU Calculator
Calculate the BTU you need to cool a room by size, sun exposure, and occupants. Get the recommended air conditioner capacity in BTU and tons.
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Furnace Size Calculator
Size a furnace in BTU from square footage, climate zone, insulation and AFUE. See the input rating to shop for, output BTU needed and load per square foot.
Open calculatorHeating & Cooling estimating FAQ
What can I estimate with the heating & cooling calculators?
Size air conditioners and heating loads for a room by area, sun exposure, and occupancy. Each tool shows the formula and a worked example so you can see exactly how the result is produced.
Do these tools include labor and tax?
Unless a calculator explicitly asks for a price that includes labor, results cover materials and quantities only. Add labor, tax, and delivery from local quotes for a full budget.
Are the calculators free?
Yes — all calculators are free, run in your browser, and require no account.