Water Heater GPM Calculator

GPM Formula:

\[ GPM = \frac{BTU}{500 \times \Delta T} \]

GPM (gal/min):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is a Water Heater GPM Calculator?

Definition: This calculator determines the gallons per minute (GPM) capacity of a water heater based on its BTU rating and temperature rise.

Purpose: It helps HVAC professionals and homeowners understand the hot water delivery capacity of their water heating systems.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ GPM = \frac{BTU}{500 \times \Delta T} \]

Where:

\( GPM \) — Gallons per minute capacity
\( BTU \) — British Thermal Units per hour
\( \Delta T \) — Temperature rise in degrees Fahrenheit
500 — Constant (BTU required to raise 1 gallon of water by 1°F in 1 hour)

Explanation: The formula calculates how many gallons of water can be heated per minute given the heater's BTU output and desired temperature increase.

3. Importance of GPM Calculation

Details: Proper GPM estimation ensures your water heater can meet demand during peak usage times and helps with system sizing and selection.

4. Using the Calculator

Tips: Enter the water heater's BTU rating and desired temperature rise (default 70°F). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical ΔT value?
A: Standard calculations use 70°F (from 50°F inlet to 120°F outlet), but adjust based on your actual incoming water temperature.

Q2: How do I find my water heater's BTU rating?
A: Check the manufacturer's specifications or the rating plate on the unit.

Q3: Why is 500 used in the formula?
A: It's the approximate number of BTUs needed to raise 1 gallon of water by 1°F in 1 hour (including efficiency losses).

Q4: What GPM is needed for a household?
A: Typical homes need 2-5 GPM depending on the number of bathrooms and fixtures.

Q5: Does this account for simultaneous use?
A: No, consider peak demand when sizing your water heater.