1. What is an Electric Tankless Water Heater GPM Calculator?

Definition: This calculator estimates the flow rate (gallons per minute) that an electric tankless water heater can deliver based on its power and desired temperature rise.

Purpose: Helps homeowners and plumbers determine if a tankless heater can meet the hot water demands for showers, faucets, and appliances.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( GPM \) — Flow rate in gallons per minute
• \( kW \) — Heater power in kilowatts
• \( \Delta T \) — Temperature rise in °F (desired output - incoming water temp)
• \( 0.139 \) — Conversion factor (BTU/min per kW per °F)

Explanation: The formula calculates how much water can be heated per minute given the heater's power and desired temperature increase.

3. Importance of GPM Calculation

Details: Proper flow rate estimation ensures your tankless heater can provide enough hot water for simultaneous uses without temperature fluctuations.

4. Using the Calculator

Tips: Enter the heater's power in kW and desired temperature rise (typically 70°F for shower use). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical temperature rise for showers?
A: Most showers need about 70°F rise (from 50°F incoming to 120°F output).

Q2: How many GPM do I need for a home?
A: A standard shower uses 2.0-2.5 GPM. Add GPM requirements for all simultaneous uses.

Q3: What if my calculated GPM is too low?
A: Consider a higher kW unit, installing multiple units, or reducing simultaneous hot water use.

Q4: Does this account for voltage or efficiency?
A: The kW input should be the actual power output. Most residential units are 90-99% efficient.

Q5: What's the 0.139 constant represent?
A: It's the conversion factor accounting for water's specific heat and unit conversions (8.33 lb/gal × 60 min/hr × 1 BTU/lb°F ÷ 3412 BTU/kWh).