All HVAC calculators
16 calculators, grouped by topic. Each one opens with a worked example you can change.
Sizing & Loads
BTU, tons and heat loss- AC BTU CalculatorFind the BTU rating for a room air conditioner or single-zone mini-split from room size, sun exposure, occupancy and kitchen use.
- AC Tonnage CalculatorEstimate what size central air conditioner or heat pump (in tons) a house needs from its size, climate, insulation and windows — not just square footage.
- HVAC Load CalculatorBlock-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.
- Furnace Sizing CalculatorEstimate a home’s heating BTU requirement (design heat loss) and the furnace input rating needed at a given AFUE.
Energy & Operating Cost
Running cost and efficiency- AC Electricity Cost CalculatorEstimate what an air conditioner costs to run per hour, day, month and cooling season from its capacity and SEER2 rating, or from its measured power draw.
- SEER2 Energy Savings CalculatorEstimate annual cooling energy and cost savings from upgrading to a higher SEER2 air conditioner or heat pump, with simple payback.
- Heating Cost CalculatorCompare the cost of delivered heat from natural gas, propane, heating oil, electric resistance and a heat pump, per million BTU and per year.
Airflow & Ducts
CFM, ducts and delta T- CFM CalculatorCalculate the airflow (CFM) needed to carry a heating or cooling load at a given temperature difference, or to achieve a target number of air changes in a room.
- CFM per Ton CalculatorCheck whether a system’s airflow suits its cooling capacity, or find the target blower airflow for a given tonnage.
- Duct Size CalculatorSize round and rectangular ducts for a given airflow by the equal-friction or velocity method, with friction loss and velocity at the nearest standard size.
- Air Changes per Hour CalculatorConvert between airflow (CFM) and air changes per hour (ACH) for any room or building.
- Cooling Capacity CalculatorMeasure delivered cooling capacity — sensible, latent and total BTU/h — from airflow and the dry-bulb and wet-bulb temperatures across the evaporator coil.
- HVAC Temperature Split CalculatorCalculate the return-to-supply temperature difference (delta T) across an AC coil or furnace and see what it suggests about airflow and performance.
Psychrometrics
Humidity, dew point, enthalpyUnit Conversions
BTU, tons, kW, °F/°C- BTU to Tons ConverterConvert heating and cooling capacity between BTU/h, tons of refrigeration, kW, watts, MBH, kcal/h and horsepower.
- Fahrenheit to Celsius ConverterConvert temperatures and temperature differences between Fahrenheit, Celsius, Kelvin and Rankine — including the HVAC-critical difference between a reading and a delta.