1. What is a Water Heater Sizing Calculator?

Definition: This calculator determines the First Hour Rating (FHR) of a storage water heater, which measures how much hot water the unit can supply in one hour of peak demand.

Purpose: Helps homeowners and plumbers properly size water heaters to meet household hot water needs.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( FHR \) — First Hour Rating (gallons per hour)
• \( T \) — Tank Capacity (gallons)
• \( R \) — Recovery Rate (gallons per hour)

Explanation: The formula accounts for 70% of the tank's capacity plus the heater's ability to recover (heat) more water during that first hour.

3. Importance of Proper Water Heater Sizing

Details: Correct sizing ensures adequate hot water supply while maximizing energy efficiency and preventing premature equipment failure.

4. Using the Calculator

Tips: Enter the tank capacity in gallons and the recovery rate in gallons per hour. Both values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: Why multiply tank capacity by 0.70?
A: This accounts for the fact that about 70% of the tank's hot water is usable before the temperature drops significantly.

Q2: Where do I find the recovery rate?
A: Check your water heater's specifications - it's typically listed in the product documentation or on the Energy Guide label.

Q3: What's a good FHR for my home?
A: This depends on your household size and water usage patterns. A typical family of 4 might need 50-75 gallons in the first hour.

Q4: Does this work for tankless water heaters?
A: No, tankless heaters are sized differently based solely on flow rate and temperature rise requirements.

Q5: Should I round up my FHR result?
A: Yes, it's recommended to round up to the nearest standard water heater size to ensure adequate capacity.