Home HVAC calculators
Free, no-signup heating & cooling calculators for homeowners, DIYers and system buyers — AC / furnace / heat-pump sizing, running cost on the rate you enter, efficiency-upgrade savings, heat-pump-vs-furnace fuel comparison, replacement budgeting and humidity/ventilation comfort. Every tool shows its formula, a worked example and a reference table.
Sizing & Load
What size AC, furnace, heat pump or mini-split? BTU & tonnage from area, climate zone and adjustments — plus ton/BTU/kW and airflow.
All Sizing & Load tools →Running Cost
What it costs to run — AC, heat pump and furnace — on the energy rate you enter, plus electric-vs-gas and thermostat setback.
All Running Cost tools →Efficiency & Savings
Annual savings & payback of a SEER2, AFUE or HSPF2 upgrade on your own upgrade cost, plus EER↔SEER and COP↔HSPF conversions.
All Efficiency & Savings tools →Heat Pump vs Furnace
Delivered $/MMBTU by fuel, heat-pump-vs-furnace on your rates, the economic balance point and COP at temperature.
All Heat Pump vs Furnace tools →Replacement & Cost
Budget from the prices you enter: $/ton worksheet, full-system line items, a two-quote normalizer and simple financing.
All Replacement & Cost tools →Comfort & Air
Humidity, ventilation and airflow: dehumidifier sizing, ASHRAE 62.2 CFM, air changes per hour, duct CFM, dew point and heat index.
All Comfort & Air tools →Sizing & Load
Running Cost
Efficiency & Savings
Heat Pump vs Furnace
Replacement & Cost
Comfort & Air
Built for the whole decision — and to stay correct forever
ClimateCalcs gathers the calculations homeowners and buyers reach for across the whole heating & cooling decision — size, running cost, efficiency, fuel switch, replacement and comfort — in one focused hub, in US units, without signup, with transparent formulas. Every tool shows not just the answer but the underlying formula, a worked example and a reference table.
Because the tools rest on timeless building-science math and stable constants (1 ton = 12,000 BTU/h, 1 kWh = 3,412 BTU, 1 therm = 100,000 BTU, ~400 CFM/ton, ASHRAE 62.2 rates, the DOE 2023 SEER2/HSPF2 test basis), they stay correct with no maintenance — no energy prices, no equipment price database, no live feeds. Cost tools use the rate you enter from your own bills and quotes. More at Sources & formulas, Methodology and About.
Estimates, not engineering. Sizing results are a starting point — a professional Manual J / Manual S load calculation is required before buying equipment; gas, electrical and refrigerant work must be done by licensed pros; install CO alarms.