HVAC Calculators

Every HVAC and refrigeration calculator on the site, grouped by the job. Each one shows the formula and the steps with your numbers, keeps its inputs in the link so you can share or repeat a result, and prints a dated record. Nothing you type is uploaded.

Cooling and heating sizing

• BTU calculator — BTU/h for a room: cooling from the ENERGY STAR chart, heating from heat loss.
• AC size calculator — cooling capacity in BTU/h and tons, and the nominal AC size for your square footage.
• Mini split BTU calculator — BTU per room, indoor head sizes and the outdoor unit for 1–5 zones.
• Furnace size calculator — whole-house heat loss, furnace output and input for its AFUE.
• Boiler size calculator — boiler BTU for heating, combi boiler kW for hot water, cylinder reheat.
• Radiator BTU calculator — room heat loss and the radiator output you need at ΔT50.
• Chiller tonnage calculator — tons from chilled-water flow and ΔT, or from a process load.
• BTU to kW converter — BTU/h, kW, watts, tons of refrigeration and hp.

Ducts and airflow

• Duct size calculator — round and rectangular duct size from CFM and friction rate or velocity.
• Duct sizing chart — CFM capacity of round and rectangular ducts at a chosen friction rate.
• CFM calculator — airflow from air changes per hour, heat load, tons, duct velocity or bathroom size.

Psychrometrics

• Psychrometric calculator — every moist-air property from two readings, with a chart point.
• Dew point calculator — dew point from temperature and relative humidity or wet bulb.
• Wet bulb calculator — wet-bulb temperature from temperature and humidity, and WBGT.

Refrigerants

• Refrigerant PT chart — pressure temperature chart and lookup for 11 refrigerants.
• Superheat and subcooling calculator — superheat, subcooling and target superheat from gauge readings.
• PT charts by refrigerant: R-410A · R-22 · R-32 · R-454B · R-134a · R-404A · R-407C · R-448A · R-290

All results are estimates for planning: check critical designs against the applicable standard and the equipment manufacturer’s data. Results may be used freely in commercial work such as quotes, proposals and reports.