HVAC sizing and load calculators
Estimate heating and cooling loads and the equipment size a room or house needs — with the assumptions shown, and clear limits on what an estimate can tell you.
AC BTU Calculator
Find the BTU rating for a room air conditioner or single-zone mini-split from room size, sun exposure, occupancy and kitchen use.
Answers: What size (BTU) air conditioner do I need for a room?
AC Tonnage Calculator
Estimate what size central air conditioner or heat pump (in tons) a house needs from its size, climate, insulation and windows — not just square footage.
Answers: What size AC unit (tons) do I need for my house?
HVAC Load Calculator
Block-load estimate of a home’s heating and cooling loads from envelope R-values, window U-factor and SHGC, air leakage and design temperatures, with a component breakdown.
Answers: Estimate heating and cooling loads (BTU/h) for HVAC sizing from building details.
Furnace Sizing Calculator
Estimate a home’s heating BTU requirement (design heat loss) and the furnace input rating needed at a given AFUE.
Answers: What size furnace (BTU) do I need for my house?
Which sizing calculator to use
- One room, a window unit or a single mini-split head: the AC BTU Calculator.
- A central air conditioner or heat pump for a whole house: the AC Tonnage Calculator.
- A furnace: the Furnace Sizing Calculator, which also converts heat loss to an input rating at your AFUE.
- You have R-values, window ratings and design temperatures: the HVAC Load Calculator, with a component breakdown.
Estimates are not a Manual J
Building codes require ACCA Manual J for residential equipment sizing, and Manual J works room by room with detailed construction data. These calculators use the same physics in a simplified whole-house form. They are good for checking whether a quote is in a sensible range, planning an upgrade, or learning what drives a home’s load — not for replacing the contractor’s calculation.