Hot Water Heater Recovery Rate Calculator
Gas (Natural/Propane)
Electric
What is a Hot Water Heater Recovery Rate?
The recovery rate of a water heater is the amount of water it can heat to a specific temperature rise within one hour. This metric is crucial for determining if a water heater can keep up with the demands of your household, especially during peak usage times like morning showers or running the dishwasher.
How to Calculate Recovery Rate
The math behind recovery rate depends on the energy source and the temperature rise required. Temperature rise is the difference between the cold water entering the tank (inlet) and the hot water setting (target).
The Formula for Gas Heaters:
Recovery (GPH) = (BTU Input × Efficiency) / (8.33 × Temperature Rise)
The Formula for Electric Heaters:
Recovery (GPH) = (Wattage / 2.42) / Temperature Rise
Key Variables Explained
- BTU/Wattage: This is the power input. Gas heaters are rated in BTUs, while electric heaters use Watts.
- Efficiency: No heater is 100% efficient at transferring heat to water. Standard gas heaters typically range from 70% to 80% efficiency, while electric heaters are often near 98%.
- Temperature Rise: If your groundwater is 50°F and you want 120°F water, your rise is 70°F. The larger the rise, the slower the recovery.
Example Calculation
Imagine a 40,000 BTU gas water heater with 80% efficiency. If you need to raise the water temperature from 50°F to 120°F (a 70-degree rise):
1. (40,000 × 0.80) = 32,000 BTUs of actual heat transfer.
2. 8.33 (lbs per gallon) × 70 (rise) = 583.1.
3. 32,000 / 583.1 = 54.88 Gallons Per Hour (GPH).