1. What is a Tankless Water Heater GPM Rating?

Definition: This calculator determines the required flow rate (in gallons per minute) for a tankless water heater based on your peak water usage.

Purpose: It helps homeowners and plumbers properly size a tankless water heater to meet household hot water demands.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( Q \) — Total GPM rating needed
• \( Q_i \) — Flow rate of each individual fixture

Explanation: The calculator sums the flow rates of all fixtures that might run simultaneously during peak usage.

3. Importance of Proper GPM Rating

Details: An undersized tankless water heater will struggle to meet demand, while an oversized unit wastes energy and money.

4. Using the Calculator

Tips: Enter the flow rate for each fixture in your home. Default values are provided for typical fixtures.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical shower flow rate?
A: Standard showerheads use 2.5 GPM, while low-flow models use 1.5-2.0 GPM.

Q2: How do I know my actual fixture flow rates?
A: Check manufacturer specs or measure by timing how long it takes to fill a 1-gallon container.

Q3: Should I include all fixtures in my home?
A: Only include fixtures that might run simultaneously during peak usage times.

Q4: What if I have high-efficiency appliances?
A: Adjust the flow rates accordingly (e.g., 1.0 GPM for efficient dishwashers).

Q5: Should I add a safety margin?
A: Consider adding 10-20% to the calculated GPM for future needs or occasional high demand.