1. What is a Tankless Water Heater Gas Calculator?

Definition: This calculator estimates the required BTU (British Thermal Units) output for a gas tankless water heater based on flow rate and desired temperature rise.

Purpose: It helps homeowners and plumbers properly size gas tankless water heaters for residential or commercial applications.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( BTU \) — British Thermal Units per hour (BTU/h)
• \( GPM \) — Flow rate in gallons per minute
• \( \Delta T \) — Temperature rise in degrees Fahrenheit
• \( 500 \) — Constant (1 gallon of water raised 1°F requires about 500 BTU)

Explanation: The formula calculates the energy required to heat water at a specific flow rate to your desired temperature rise.

3. Importance of Proper Sizing

Details: Correctly sizing a tankless water heater ensures adequate hot water supply while maximizing energy efficiency and preventing overloading.

4. Using the Calculator

Tips: Enter your maximum expected flow rate (GPM) and the temperature rise needed (difference between incoming water temp and desired output temp). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical GPM for residential use?
A: Most homes need 5-7 GPM for simultaneous use of 2-3 fixtures (shower + sink + dishwasher).

Q2: What temperature rise is typical?
A: For 120°F output with 50°F incoming water, you'd need a 70°F rise. Adjust based on your climate and preferences.

Q3: Why is the constant 500?
A: It accounts for the specific heat of water (8.33 lbs/gal × 60 min/hr × 1 BTU/lb-°F ≈ 500).

Q4: Should I add a safety factor?
A: Many professionals add 10-20% to the calculated BTU to account for peak demand and efficiency losses.

Q5: How does this relate to natural gas vs propane?
A: The BTU requirement is the same, but the gas input (measured in BTU) will determine which model you need.