1. What is a Tankless Water Heater BTU Calculator?

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

Purpose: It helps homeowners and plumbers properly size 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 (weight of 1 gallon of water × minutes in an hour ÷ specific heat capacity)

Explanation: The formula calculates the energy required to heat a given flow of water by a specified temperature rise.

3. Importance of Proper BTU Calculation

Details: Correct BTU sizing ensures your tankless water heater can meet hot water demand without temperature fluctuations or excessive energy use.

4. Using the Calculator

Tips:

• Measure your peak flow rate (GPM) by adding up all fixtures that might run simultaneously
• Determine your needed temperature rise (ΔT) by subtracting incoming water temperature from desired output temperature
• All values must be > 0

5. Frequently Asked Questions (FAQ)

Q1: What's a typical temperature rise for residential use?
A: Most homes need 45-70°F rise depending on incoming water temperature and desired output (typically 120°F).

Q2: How do I measure my flow rate (GPM)?
A: Time how many seconds it takes to fill a 1-gallon container, then divide 60 by that number.

Q3: Why is the constant 500 in the formula?
A: It combines the weight of water (8.33 lb/gal), minutes per hour (60), and water's specific heat (1 BTU/lb/°F).

Q4: What if my calculated BTU is between standard unit sizes?
A: Always round up to the next available size to ensure adequate capacity.

Q5: Does this account for simultaneous use of multiple fixtures?
A: Yes, if you enter the total GPM of all fixtures that might run together.