HVAC & Climate Calculators
Tools for HVAC technicians, installers and building designers. Load estimates are clearly labeled rule-of-thumb methods; duct sizing uses the standard equal-friction equation for round galvanized duct.
Load Estimation
Estimate heating and cooling loads for rooms and buildings.
- BTU CalculatorEstimate the cooling load in BTU/h for any room from floor area, climate, insulation, sun exposure, occupants and appliances. Includes tonnage and CFM guidance.
- Heating Load CalculatorEstimate heating load in BTU/h and kW from floor area, design temperature difference and insulation quality. Includes ventilation adjustment guidance.
- Degree-Day Heating CalculatorEstimate heating fuel use and cost from degree-days and house heat-loss coefficient. Supports gas, oil, propane and electric heating.
Airflow & Ducts
Size ducts, check velocity, convert between CFM and air changes, and apply the sensible heat equation.
- Duct Size CalculatorSize round HVAC ducts from airflow (CFM) and friction rate using the ASHRAE equal-friction method. Gives exact diameter, nominal size, velocity and metric equivalent.
- Airflow / ACH CalculatorConvert between airflow (CFM, L/s, m³/h) and air changes per hour for any room volume. Includes typical ACH targets for bedrooms, bathrooms and kitchens.
- Duct Velocity CalculatorCheck air velocity in a known duct: enter CFM and diameter to get fpm, m/s, duct area and the estimated friction rate. Includes noise guidance.
- Fan Laws CalculatorApply the fan affinity laws: how airflow, static pressure and power change with fan speed. The cubic power law explains VFD energy savings.
- Sensible Heat & Airflow CalculatorSolve the sensible heat equation: find airflow from BTU/h and ΔT, or BTU delivered from known airflow. Metric equivalent included.
Comfort & Weather
Dew point, heat index and wind chill — the metrics that translate temperature and humidity into human comfort.
- Dew Point CalculatorCalculate dew point and approximate wet-bulb from temperature and humidity, with comfort interpretation. Magnus formula, °C and °F.
- Heat Index CalculatorCalculate the heat index (feels-like temperature) from air temperature and humidity using the official NWS Rothfusz regression, with risk levels.
- Wind Chill CalculatorCalculate wind chill from temperature and wind speed using the official NWS formula, with frostbite time estimates for exposed skin.
Air Properties & Heat Pumps
Air density, psychrometric state points, heat pump COP at temperature, and exact temperature conversion.
- Air Density CalculatorCalculate moist air density from temperature, altitude and humidity, with the correction factor for fan CFM and the 1.08 sensible-heat equation.
- Psychrometric CalculatorCalculate humidity ratio, enthalpy and dew point from dry-bulb temperature and relative humidity, with altitude-corrected barometric pressure. ASHRAE correlations.
- Heat Pump COP CalculatorConvert heat pump HSPF to COP at your outdoor temperature, and compare heating cost against electric resistance — with capacity derating shown.
- Temperature Conversion CalculatorConvert between Celsius, Fahrenheit and Kelvin exactly, with HVAC-specific ΔT guidance — the difference conversion (×1.8) that load math depends on.
Efficiency & Cost
SEER/EER/COP conversions and air conditioning running costs.
- SEER / EER / COP ConverterConvert SEER to EER, COP and kW per ton of cooling. Understand what efficiency ratings mean for real electricity costs and how the ratings differ.
- AC Running Cost CalculatorCalculate air conditioning running cost from tonnage, SEER, runtime and electricity rate. Monthly and seasonal figures for upgrade comparisons.
Design guide
How these calculations fit together in real projects — the order to run them in, and the decisions each one answers.