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Free HVAC Tools & Calculators

Fast, free calculators for working HVAC and refrigeration techs — and students learning the trade. Refrigerant charging, airflow, gas heating, electrical, psychrometrics, load sizing, and unit conversions, right on your phone. No account required.

Refrigeration

Superheat Calculator

Calculate measured superheat from suction line temperature and saturation temperature, with TXV and fixed-orifice target guidance.

Refrigeration

Subcooling Calculator

Calculate measured subcooling from liquid saturation temperature and liquid line temperature, with TXV charging targets.

Refrigeration

Target Superheat Calculator

Find the target superheat for a fixed-orifice system from indoor wet-bulb and outdoor dry-bulb temperatures.

Refrigeration

Compression Ratio Calculator

Calculate a system's compression ratio from discharge and suction pressure, with healthy-range guidance.

Refrigeration

Line-Set Charge Calculator

Estimate the additional refrigerant charge for liquid line beyond the factory-charged length, by line diameter.

Refrigeration

PT Chart (Pressure-Temperature)

Convert pressure to saturation temperature (and back) for 9 common refrigerants, with bubble/dew points for glide blends.

Airflow

Delta T Calculator

Calculate the temperature split (Delta T) across the evaporator coil from return and supply air temperatures.

Airflow

CFM & Tonnage Calculator

Find required CFM from sensible heat and Delta T, apply the 400 CFM/ton rule, and convert tons, BTU/h, and kW.

Airflow

Static Pressure Calculator

Add supply and return static pressure readings to get TESP and compare it to the equipment's rated maximum.

Airflow

Duct Size & Velocity Calculator

Find air velocity from CFM and duct size (round or rectangular), plus equivalent diameter, against Manual D target ranges.

Airflow

Fan Laws Calculator

See how blower CFM, static pressure, and brake horsepower change with RPM using the three fan laws.

Heating & Gas

Furnace Temp Rise Calculator

Find furnace temperature rise and the resulting heating CFM from BTU output and supply/return temperatures.

Heating & Gas

Gas Meter Clocking Calculator

Time one gas meter dial revolution to find actual BTU/h input and cubic feet per hour.

Electrical

Capacitor (MFD) Calculator

Calculate a run capacitor's microfarad (µF) value from measured amps and voltage, and check it against the rating.

Electrical

Ohm's & Watt's Law Calculator

Enter any two of volts, amps, ohms, and watts to solve the other two via Ohm's and Watt's law.

Electrical

Voltage Drop Calculator

Calculate single- or three-phase voltage drop and percent drop from wire gauge, length, and current.

Psychrometrics

Sensible & Latent Heat Calculator

Find sensible, latent, and total heat (BTU/h) from CFM and temperature, moisture, or enthalpy change, plus SHR.

Psychrometrics

Dew Point & RH Calculator

Find dew point from temperature and RH (or RH from temperature and dew point), with condensation-risk flags.

Load & Sizing

Load Estimate Calculator

Rough ballpark cooling BTU and tonnage from square footage and climate — for budgeting only, never final sizing.

Conversions

HVAC Unit Converter

Convert tons/BTU/kW, °F/°C, SEER/EER/COP, PSI/kPa, and lb/kg — the everyday HVAC unit conversions in one place.

These calculators are provided for quick field reference and estimation. Always follow equipment manufacturer specifications and applicable codes. FieldPad is not a substitute for professional engineering or manufacturer charging data.

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