1. What is a Gas Tankless Water Heater Sizing Calculator?

Definition: This calculator estimates the required flow rate (in gallons per minute) for a gas tankless water heater based on your household's simultaneous hot water needs.

Purpose: It helps homeowners and plumbers properly size a tankless water heater to ensure adequate hot water supply for large families (typically needing 10 GPM capacity).

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( Q \) — Total flow rate required (gallons per minute)
• \( Q_i \) — Flow rate of each individual fixture

Explanation: The calculator sums the flow rates of all fixtures that might run simultaneously to determine the total demand on your tankless water heater.

3. Importance of Proper Sizing

Details: Correct sizing ensures your tankless water heater can meet peak demand without temperature fluctuations or insufficient flow. Undersizing leads to cold water sandwiches, while oversizing wastes energy.

4. Using the Calculator

Tips: Enter the flow rates for all potential simultaneous fixtures. Default values represent typical flow rates:

• Shower: 2.5 GPM
• Sink: 1.5 GPM
• Dishwasher: 1.5 GPM
• Washing Machine: 2.0 GPM

5. Frequently Asked Questions (FAQ)

Q1: Why size for 10 GPM?
A: 10 GPM covers simultaneous use of multiple fixtures in large households (e.g., two showers plus a dishwasher).

Q2: What if my calculated flow exceeds 10 GPM?
A: Consider a larger unit, multiple units in parallel, or staggering high-demand appliance use.

Q3: Do I need to account for temperature rise?
A: This calculator focuses on flow rate. For complete sizing, you'll also need to consider the temperature rise needed (typically 70°F for most climates).

Q4: How can I reduce my required GPM?
A: Install low-flow fixtures (1.5 GPM showerheads, 0.5 GPM faucet aerators) or schedule high-demand appliances at different times.

Q5: What's the typical GPM for a family of 4?
A: Most families of 4 need 7-10 GPM capacity depending on fixture types and usage patterns.