HVAC and Plumbing Calculators
Free calculators for the math HVAC techs and plumbers do in the field and at the design desk, starting with airflow, duct and furnace sizing.
Each tool is built on published engineering methods, explains its formula, and walks through a worked example so you can check the answer yourself.
Airflow and Ducts
Work out airflow and size supply and return ducts.
- Open calculator
CFM Calculator
Calculate CFM from room size and air changes, from a BTU load and temperature difference, from duct size and velocity, or for code ventilation.
- Open calculator
Duct Size Calculator
Size HVAC ducts from CFM and friction rate, with a velocity limit. Get the standard round size, rectangular options, or check friction on an existing duct.
Heating Equipment
Estimate the heating load and pick a furnace size.