1. What is an Electric Water Heater Size Calculator?

Definition: This calculator determines the First Hour Rating (FHR) of an electric water heater based on tank capacity and recovery rate.

Purpose: It helps homeowners and plumbers select the properly sized water heater for household 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 recovery rate in one hour.

3. Importance of First Hour Rating

Details: FHR indicates how much hot water the heater can supply during a busy hour, helping ensure adequate supply during peak usage.

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: What is First Hour Rating?
A: FHR measures how many gallons of hot water the heater can deliver in the first hour of use, starting with a full tank.

Q2: Why use 70% of tank capacity?
A: This accounts for the fact that only about 70% of the tank's hot water is typically usable before temperature drops.

Q3: How do I find my water heater's recovery rate?
A: Check manufacturer specifications or divide the heater's wattage by (2.42 × temperature rise).

Q4: What's a good FHR for my household?
A: A typical household needs 12-20 gallons per person during peak hour. Family of 4 might need 50-80 gallons FHR.

Q5: Does this work for gas water heaters?
A: The formula is similar, but gas heaters typically have higher recovery rates than electric models.