HVAC Calculators
Size air conditioners, furnaces, heat pumps, ducts, fans and generators with calculators that show every step of the math.
Calculators
AC Tonnage Calculator: What Size Air Conditioner Do You Need?Most homes land between 1.5 and 5 tons. Start near 20 BTU/h per square foot, then adjust for climate, insulation and duc…Air Changes per Hour Calculator: ACH from CFM and CFM from ACHAir changes per hour (ACH) is how many times a room's full volume of air is moved in an hour: ACH = CFM × 60 ÷ room volu…Bathroom Fan CFM Calculator: What Size Exhaust Fan Do You Need?For bathrooms up to 100 sq ft, plan on 1 CFM per square foot of floor area with a 50 CFM minimum, scaled up for ceilings…BTU Conversion Calculator: BTU/h to Watts, kW, Tons, Therms and HP1 watt equals 3.412 BTU/h, so 1 kW is 3,412 BTU/h. One ton of cooling is 12,000 BTU/h (about 3.52 kW), one therm per hou…Ceiling Fan Downrod Length Calculator: Rod Size by Ceiling HeightSubtract your target blade height (about 8.5 ft) from the ceiling height, convert to inches, then subtract the fan's own…Ceiling Fan Size Calculator: Blade Span for Your Room SizeMatch blade span to floor area: about 30–36 inches for rooms up to 75 sq ft, 36–44 inches up to 144 sq ft, 44–52 inches …CFM Calculator: System Airflow per Ton and Room CFM from BTU or SizeA central air conditioner usually moves 350–450 CFM of air per ton, with 400 CFM per ton the common default, so a 3-ton …Duct Size Calculator: Round Duct Diameter from CFM and VelocityDivide the airflow in CFM by the design velocity in feet per minute to get the duct's cross-sectional area, then convert…COP Calculator: Coefficient of Performance from Watts, EER or HSPFCOP is useful heat moved divided by the energy used to move it, with both in the same units. A heat pump that delivers 3…Furnace Sizing Calculator: BTU Output, Input and AFUE by Climate ZoneFurnaces are sold by input BTU/h, but your house needs a certain output. Estimate the heat loss (roughly 25–50 BTU/h per…Generator Sizing Calculator: Running Watts, Motor Surge and AC StartingA generator has to carry everything that runs at once and also survive the start-up surge of the biggest motor. Add up r…Heat Pump Sizing Calculator: Cooling Load, Balance Point and Backup HeatSize a heat pump on the cooling load first, so it dehumidifies well in summer, then check the heating side. Find the bal…Heating BTU Calculator: Estimate Your Home's Heat LossHeat loss is the house's total UA (opaque envelope, plus windows and doors at U-value × area) multiplied by the design t…Heating Cost Calculator: Gas, Propane, Oil, Electric and Heat PumpTo compare heating fuels fairly, convert each price to dollars per million BTU of heat delivered: price ÷ (energy per un…How Many BTU Air Conditioner Do I Need? Room and Whole-Home CalculatorStart with about 20 BTU/h per square foot of floor area (length × width), adjust for the type of room, insulation, sun a…Mini-Split Sizing Calculator: BTU per Zone and Indoor Head SizeSize a mini-split one zone at a time. Start near 20 BTU/h per square foot, adjust for ceiling height, sun, climate and p…Sones to Decibels Converter: How Loud Is a Fan Rating Really?A common approximation for fan noise is dB ≈ 33.22 × log10(sones) + 28, so 1 sone is about 28 dB, 2 sones about 38 dB an…Tankless Water Heater Size Calculator: GPM, Temperature Rise and BTUA tankless heater is sized by peak flow and temperature rise, not by tank gallons. Add the flow of fixtures used at the …