Plumbing & HVAC calculators
Pipe, pump, duct, gas, and refrigeration calculators for plumbers and HVAC techs, checked against published tables where they exist.
- Duct Size CalculatorRound duct diameter = (0.109136 × CFM^1.9 ÷ friction rate)^(1/5.02), and a rectangular duct is equivalent when its Huebscher equivalent diameter matches.Inputs: Airflow, Friction rate, Rectangular duct height
- Gas Pipe Sizing CalculatorSize the pipe so its capacity at your longest length and allowed pressure drop covers the total BTU load, using IFGC Equation 4-1 for pressures under 1.5 psi.Inputs: Gas, Total connected load, Heating value of the gas
- Hazen-Williams Friction Loss CalculatorFriction loss in psi per foot of pipe = 4.52 × Q^1.852 ÷ (C^1.852 × d^4.87), with flow Q in gpm and inside diameter d in inches.Inputs: Flow rate, Pipe inside diameter, Pipe length
- Hydronic Heat Flow CalculatorFor water, heat flow in BTU/hr equals 500 × gpm × temperature difference in °F, so 10 gpm across a 20°F drop carries 100,000 BTU/hr.Inputs: Find, Heat flow, Flow rate
- Pipe Volume CalculatorA pipe holds π ÷ 4 × inside diameter² × length; a 1-inch Schedule 40 pipe holds about 0.045 gallon per foot.Inputs: Pipe size, Inside diameter, Pipe length
- Pressure Tank Drawdown CalculatorUsable drawdown is the tank volume times the acceptance factor, P₁ ÷ P₂ − P₁ ÷ P₃ in absolute pressure, where P₁ is precharge, P₂ cut-in, and P₃ cut-out.Inputs: Total tank volume, Pump cut-in pressure, Pump cut-out pressure
- Pump Total Dynamic Head CalculatorTotal dynamic head is the vertical lift plus the pressure head plus friction loss in the pipe and fittings, plus a small velocity head.Inputs: Flow rate, Vertical lift, Required discharge pressure
- Radiant Floor Tubing CalculatorTubing length in the floor = area × 12 ÷ spacing in inches, then divide it into loops no longer than the maker's limit and add the leads to the manifold.Inputs: Heated floor area, Tube spacing, Maximum loop length
- Superheat and Subcooling CalculatorSuperheat is suction line temperature minus evaporator saturation temperature; subcooling is condenser saturation temperature minus liquid line temperature.Inputs: Suction line temperature, Evaporator saturation temperature, Liquid line temperature
- Water Heating Time and Energy CalculatorHeating water takes 8.34 BTU per gallon per degree Fahrenheit, so 40 gallons raised 70°F needs about 23,400 BTU, or 6.8 kWh.Inputs: Water to heat, Starting temperature, Target temperature