Skip to content
Log in Calculators

Water Heater Recovery Rate Calculator

Recovery in gallons per hour at the rise you actually have, the recovery GPH at the 90 F rating basis, and an estimated first-hour rating.

Inputs

Rating plate

Decides which checks and notes you get back.

The nameplate input for a gas unit in BTU/hr or MBH; the element watts for an electric tank (a 4,500 W element is about 15,400 BTU/hr). Switch the unit to kW if the label only gives watts.

Steady-state efficiency in percent, not the UEF. The DOE test method credits electric resistance heating with 98 percent (10 CFR 430 Subpart B Appendix E); atmospheric gas units run about 80 percent; condensing gas units 90-96 percent.

Tank and temperatures

Groundwater temperature. A 50 F inlet with a 140 F tank reproduces the 90 F rise that US recovery ratings are quoted at.

The temperature the tank recovers to.

The gallons printed in the model number, for example 40 in XG40.

The share of nominal volume you can draw at temperature before the outlet cools, because the tank destratifies as it empties. 70 percent is a common planning value. The EnergyGuide first-hour rating is the measured answer and always wins.

The draw you want to recover from. Enter 0 to use a full tank volume.

Optional cross-checks

US nameplates quote recovery in gallons per hour at a 90 F temperature rise. Leave 0 to skip the check; entering it shows whether the assumed efficiency matches the printed rating.

Bring the peak-hour demand over from the water heater size calculator. Leave 0 to skip the check.

Result

Recovery rate at your temperature rise
—
Time to recover the drawn gallons
—
Estimated first-hour rating
—
Recovery at the 90 F rating rise
—
Heat delivered to the water
—
—
—
Fuel-specific checks
—
Where this stops applying
—
Calculation details
Heat needed per gallon
—
First-hour headroom
—
Computed / nameplate recovery
—
Temperature rise
—
Usable stored gallons
—
Gallons being recovered
—

What to check

  • Rated input from the rating plate, or element wattage for an electric tank
  • Recovery GPH at 90 F rise, printed on the nameplate
  • Groundwater temperature and the thermostat setting

Standards referenced

  • DOE Uniform Energy Factor test procedure — 10 CFR Part 430, Subpart B, Appendix E · Uniform test method for measuring energy consumption of water heaters; UEF ratings on nameplates and EnergyGuide labels come from this procedure.

Related calculators

Screening estimate only. The result panel lists the limits that apply to this calculation. Verify nameplate data, rates, groundwater temperatures and installer quotes before deciding, and have gas, venting and electrical installations checked against the local code by a licensed contractor.

Saved calculations

Keep the assumptions with the result.

Save this calculation to return to the inputs, result, and report anytime.

Sign in to save Create account

Sign in or create an account to save this calculation.