Target temperature must be higher than inlet temperature.
Temperature Rise Required0 °F
Recovery Rate (100% Eff.)0 GPH
Time to Heat Full Tank0 Minutes
Energy Required per Tank0 kWh
Understanding Water Heater Recovery Rates
When selecting or troubleshooting an electric water heater, the Recovery Rate is a critical metric. It represents the amount of hot water the heater can produce in one hour after the tank has been completely depleted. Unlike gas heaters, electric water heaters are limited by the wattage of their heating elements and the electrical circuit capacity.
How the Calculation Works
This calculator uses the physics of thermodynamics to determine performance. The formula relies on the specific heat of water (1 BTU raises 1 lb of water by 1°F). The core equation used is:
GPH = (Watts × 3.412) / (8.33 × Temperature Rise)
Watts: The power rating of your heating element (commonly 4500W).
3.412: The conversion factor from Watts to BTUs per hour.
8.33: The weight of a gallon of water in pounds.
Temperature Rise: The difference between your cold ground water and your desired hot water setting.
Common Scenarios
A standard 4500-watt element with a 65°F temperature rise (raising 55°F groundwater to 120°F) typically recovers about 20 to 21 gallons per hour (GPH). If you have a large family or a soaking tub, this recovery rate determines how quickly you can shower again after depleting the tank.
Improving Performance
If your recovery rate is too slow, you generally cannot simply install a higher wattage element without upgrading your electrical wiring and breakers. However, you can effectively increase your hot water availability by:
Installing a mixing valve to store water at a higher temperature (e.g., 140°F) while delivering it at safe temperatures (120°F).
Insulating pipes to reduce heat loss during distribution.
Upgrading to a larger tank size (e.g., moving from 40 to 50 gallons) to provide a larger buffer before relying on the recovery rate.
function calculateRecovery() {
// 1. Get input values
var watts = parseFloat(document.getElementById('heaterWattage').value);
var gallons = parseFloat(document.getElementById('tankCapacity').value);
var inlet = parseFloat(document.getElementById('inletTemp').value);
var target = parseFloat(document.getElementById('targetTemp').value);
var errorDiv = document.getElementById('errorMsg');
var resultsDiv = document.getElementById('resultsArea');
// 2. Validate inputs
if (isNaN(watts) || isNaN(gallons) || isNaN(inlet) || isNaN(target)) {
alert("Please enter valid numbers in all fields.");
return;
}
if (target 0) {
timeString = hoursDisplay + " hr " + minsDisplay + " min";
} else {
timeString = minsDisplay + " Minutes";
}
document.getElementById('resTimeMins').innerHTML = timeString;
document.getElementById('resKwh').innerHTML = energyKwh.toFixed(2) + " kWh";
resultsDiv.style.display = 'block';
}