HVAC Size Calculator

Our HVAC Size Calculator gives a rule-of-thumb estimate of the cooling capacity (in BTUs and tons) your home's air conditioner or heat pump needs, a starting point before a professional load calculation. An undersized system struggles to maintain temperature, while an oversized one cycles frequently, both leading to higher energy bills and premature wear.

This is not a Manual J load calculation. The calculator multiplies square footage by a cooling rule of thumb for the climate you pick, about one ton per 500-600 square feet (24 BTU per square foot for hot, 22 for moderate, 20 for cold), then adjusts for insulation (×1.2 for poor, ×0.85 for good), ceiling height (+5% for each foot above 8 feet) and a second story (+10%). Dividing by 12,000 BTU per ton and rounding up to the next half ton gives the recommended size, and the installed-cost range is $3,000 to $7,000 per ton. ACCA's Manual J, the ANSI-recognized standard for residential equipment sizing loads that national building codes require, works out the actual house's heat gains and losses in detail, and it is what a contractor should run before you buy.

Neglecting insulation quality and window efficiency are common mistakes that can significantly skew HVAC sizing. Always consider your home's unique characteristics; a professional energy audit can reveal hidden inefficiencies. Overestimating your square footage or underestimating your climate's extreme temperatures can lead to an improperly sized system.