1. What is a Tankless Water Heater Size Calculator?

Definition: This calculator determines the required capacity (in gallons per minute - GPM) for a tankless water heater based on your household's simultaneous hot water demands.

Purpose: It helps homeowners and plumbers properly size a tankless water heater to ensure adequate hot water supply.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( GPM \) — Gallons per minute required from heater
• \( \sum(Demands) \) — Sum of all simultaneous hot water demands

Explanation: The calculator adds up the flow rates of all fixtures that might be used simultaneously to determine the total required capacity.

3. Importance of Proper Sizing

Details: Proper sizing ensures you have enough hot water when needed while avoiding overspending on an unnecessarily large unit.

4. Using the Calculator

Tips: Enter the flow rates for each fixture you might use simultaneously. Default values represent typical flow rates:

• Shower: 2.5 GPM
• Sink: 1.5 GPM
• Dishwasher: 1.0 GPM
• Washing Machine: 2.0 GPM

5. Frequently Asked Questions (FAQ)

Q1: What if my fixtures have different flow rates?
A: Measure your actual fixture flow rates or check manufacturer specifications for more accurate results.

Q2: Should I consider temperature rise?
A: This calculator determines flow requirements. Temperature rise affects the BTU capacity needed, not the GPM rating.

Q3: What about whole-house vs. point-of-use heaters?
A: For point-of-use heaters, only include fixtures served by that specific heater.

Q4: How do I account for low-flow fixtures?
A: Enter the actual flow rate of your low-flow fixtures (typically 1.5 GPM for showers, 0.5 GPM for faucets).

Q5: Should I add a safety margin?
A: It's recommended to add 10-20% to the calculated GPM to account for occasional higher demand.