What is a good recovery rate for a water heater?

For a residential gas tank, 35 to 45 gallons per hour through a 90 F rise is normal, which comes from a 36,000 to 40,000 BTU burner. For a standard electric tank with a 4,500 watt element, about 20 gallons per hour is normal. Neither figure is good or bad on its own: what matters is whether storage plus recovery covers your peak hour.

Why is my electric water heater so slow to recover?

Because a 4,500 watt element is about 15,400 BTU per hour of heat, against 36,000 BTU or more for a gas burner. That is roughly half the recovery rate for the same tank size. It is not a fault, it is the physics of the element, and it is why electric tanks are often specified a size larger than the gas tank they replace.

Do both elements in an electric tank run at once?

No. A standard residential electric tank is non-simultaneous: the upper thermostat gives priority to the upper element, and only when the top of the tank is satisfied does the lower element run. So the recovery rate is set by one element, not two, which surprises people who expect 9,000 watts from a tank holding two 4,500 watt elements.

How long does it take to heat a full tank from cold?

Divide the tank size by the recovery rate. A 50 gallon electric tank recovering 20 gallons per hour through a 90 F rise takes about two and a half hours from fully cold. The same size gas tank recovering 38 gallons per hour takes about eighty minutes. That is the figure to plan around after a heater has been off, not the first hour rating.

Sizing calculator

Water Heater Recovery Rate Calculator

Quick answer

Recovery rate is gallons per hour a heater reheats. A 36,000 BTU gas burner at 80 percent efficiency recovers about 38 gallons per hour through a 90 F rise, while a 4,500 watt electric element recovers about 20 gallons per hour through the same rise.

Result

Recovery rate 38.4 GPH Published standard

Per minute 0.64 GPM Published standard

Minutes to reheat the tank 78 min Published standard

Energy for one tankful 37,485 BTU Published standard

Recovery rate is what stops you running out on the third shower. It is also why a gas tank of the same gallons outperforms an electric one, and why a heat pump water heater in compressor-only mode feels slow despite costing far less to run.

The formula

Gas GPH = BTU/h x efficiency / (8.33 x rise). Electric GPH = kW x 3412 / (8.33 x rise).

This is the same energy balance as every other calculation on this site, rearranged. Efficiency here is thermal efficiency at the burner, which is not the same thing as the UEF on the label: UEF is measured over a whole day and includes standby loss, so it is always the lower number.

The figures above are computed with these exact inputs: Heat source gas, Burner input 36000 BTU/h, Thermal efficiency 80 %, Element rating 4.5 kW, Temperature rise 90 F, Tank size 50 gal.

What this calculator assumes

Some of these are published test procedures or code tables and some are planning conventions. They are not the same kind of number, so each one is labeled.

Assumption	Kind	Where it comes from
Water Weight: 8.33	Published standard	Published density of water at 60 F, 8.33 lb per gallon
Gas Efficiency: 0.8	Convention	Assumed thermal efficiency for an atmospheric gas burner. Use the efficiency on your own unit data plate where it is published
Btu Per Kwh: 3412.14	Published standard	Exact conversion between the international table BTU and the kilowatt hour

Gear that matches this result

Every card below is in the page source. The calculator re-ranks them against your numbers and marks anything that falls short of what you just calculated.

Intermediate

Camco

Camco 4500W 240V Foldback Element

$12.85

Low watt density, which spreads the same 4,500 watts over more surface area so it scales more slowly in hard water.

Best for: Hard water, where elements scale and burn out

Check price on Amazon

Beginner

Reliance

Reliance 4500W 240V Screw-In Element

$12.92

The plain screw-in 4,500 watt element, which is what most electric tanks use in both positions.

Best for: A straightforward element replacement

Check price on Amazon

Beginner

Rheem

Rheem SP10552MH 4500W Element

$8.99

The manufacturer part for a Rheem tank, which removes any question about gasket size and thread type.

Best for: A Rheem electric tank

Check price on Amazon

Beginner

Reliance

Reliance 9000507 Lower Thermostat

$13.96

The lower thermostat, which is the one that fails when a tank makes a little hot water and then runs cold quickly.

Best for: A tank that runs out too fast

Check price on Amazon

Intermediate

Reliance

Reliance Electric Water Heater Repair Pack

$40.02

Upper and lower thermostats together, which is the sensible way to buy them because the two are wired in series and the fault is often not obvious.

Best for: Diagnosing a no-hot-water electric tank

Check price on Amazon

Intermediate

Eastman

Eastman Dielectric Heat Trap Nipples, Pair

$11.64

Dielectric nipples separate copper from the steel tank so the joint does not corrode galvanically, and the heat trap stops convection up the pipe.

Best for: Every tank replacement with copper pipe

Check price on Amazon

Frequently asked questions

What is a good recovery rate for a water heater?: For a residential gas tank, 35 to 45 gallons per hour through a 90 F rise is normal, which comes from a 36,000 to 40,000 BTU burner. For a standard electric tank with a 4,500 watt element, about 20 gallons per hour is normal. Neither figure is good or bad on its own: what matters is whether storage plus recovery covers your peak hour.
Why is my electric water heater so slow to recover?: Because a 4,500 watt element is about 15,400 BTU per hour of heat, against 36,000 BTU or more for a gas burner. That is roughly half the recovery rate for the same tank size. It is not a fault, it is the physics of the element, and it is why electric tanks are often specified a size larger than the gas tank they replace.
Do both elements in an electric tank run at once?: No. A standard residential electric tank is non-simultaneous: the upper thermostat gives priority to the upper element, and only when the top of the tank is satisfied does the lower element run. So the recovery rate is set by one element, not two, which surprises people who expect 9,000 watts from a tank holding two 4,500 watt elements.
How long does it take to heat a full tank from cold?: Divide the tank size by the recovery rate. A 50 gallon electric tank recovering 20 gallons per hour through a 90 F rise takes about two and a half hours from fully cold. The same size gas tank recovering 38 gallons per hour takes about eighty minutes. That is the figure to plan around after a heater has been off, not the first hour rating.

Researched guidance, not professional advice. These results are planning figures from published test procedures, code tables and manufacturer specifications, and they do not replace a sizing done by the person who will sign the permit. A water heater is a pressure vessel: never cap, plug or remove the temperature and pressure relief valve, and replace one that will not open when the test lever is lifted. Gas line, flue and vent work belongs to a licensed plumber or gas fitter, because improper venting produces carbon monoxide. Water at 140 F scalds a child in seconds. Turn off the breaker before touching an element, and never energise an element that is not submerged.