1. What is an On Demand Water Heater Size Calculator?

Definition: This calculator estimates the required flow rate (in gallons per minute) for an on-demand water heater based on the number of fixtures and their flow rates.

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

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( GPM \) — Gallons per minute required
• \( Fixtures \) — Number of fixtures that may run simultaneously
• \( Flow\ Rate \) — Average flow rate per fixture (gal/min)

Explanation: The total flow rate is calculated by multiplying the number of fixtures by their individual flow rates.

3. Importance of Proper Sizing

Details: Correct sizing ensures your tankless water heater can meet simultaneous hot water demands without temperature fluctuations or insufficient flow.

4. Using the Calculator

Tips: Enter the number of fixtures that might run simultaneously and the average flow rate per fixture (default 1.5 gal/min). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical flow rate for fixtures?
A: Standard flow rates: shower (1.5-2.5 gpm), faucet (0.5-1.5 gpm), dishwasher (1-2 gpm), washing machine (1.5-3 gpm).

Q2: Should I count all fixtures in my home?
A: No, only count fixtures that might run simultaneously during peak usage.

Q3: What if my fixtures have different flow rates?
A: Use a weighted average or calculate each fixture separately and sum the results.

Q4: How does temperature rise affect sizing?
A: This calculator provides flow rate only. For complete sizing, consider your required temperature rise and the heater's specifications.

Q5: Should I add a safety factor?
A: Many professionals recommend adding 10-20% to the calculated GPM for safety margin.