Free tools
Water heater calculators
Every calculator here runs in your browser, needs no sign-up, and uses the same engine as the iPhone app.
- Water heater size calculatorFree water heater size calculator. Get the minimum First Hour Rating for a tank or the GPM and BTU/hr a tankless unit needs at your temperature rise.
- Tankless sizing calculatorSize a tankless water heater: flow in GPM at your temperature rise, heat load in BTU/hr, gas input at your efficiency and electric kW. Free, no sign-up.
- Is my water heater big enough?Check whether a specific tank or tankless water heater meets your household's peak demand using its First Hour Rating or rated GPM from the spec sheet.
- Electric tankless kW & ampsHow many kW and amps an electric tankless water heater needs for your flow and temperature rise, and why cold-climate homes often need more than they expect.
- Recovery rate calculatorCalculate a tank water heater's recovery rate in gallons per hour from input, efficiency and temperature rise, and how recovery relates to First Hour Rating.
Water Heater Sizing Calculator for iPhone
Take the calculator to the job site
The app runs the same sizing engine as this site, offline. Basic tank and tankless sizing is free. Lifetime Pro, a one-time $4.99 purchase, adds tank vs. tankless comparison, custom fixtures, saved jobs with notes and PDF reports you can send to a customer.
Coming soon to theApp Store
