1. What is a Water Heater BTU Calculator?

Definition: This calculator estimates the heat output in BTUs per hour for a water heater based on flow rate and temperature rise.

Purpose: It helps HVAC professionals and plumbers determine the required capacity for water heating systems.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( Q_{btu} \) — Heat output (BTU/hour)
• \( Q \) — Water flow rate (gallons per minute)
• \( \Delta T \) — Temperature rise (°F)
• 500.4 — Constant combining water density and specific heat

Explanation: The formula calculates the energy required to heat a given flow of water by a specified temperature difference.

3. Importance of BTU Calculation

Details: Proper BTU calculation ensures adequate hot water supply, energy efficiency, and correct sizing of heating equipment.

4. Using the Calculator

Tips: Enter the water flow rate in GPM and desired temperature rise in °F. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: Why is 500.4 used in the formula?
A: This constant combines water's density (8.33 lb/gal) and specific heat (1 BTU/lb-°F) with unit conversion factors.

Q2: What's a typical temperature rise for residential systems?
A: Most systems are designed for a 70°F rise (from 50°F incoming to 120°F output).

Q3: How does flow rate affect BTU requirements?
A: BTU requirements increase linearly with flow rate - double the flow requires double the BTUs for same ΔT.

Q4: What if I need to heat to a specific temperature?
A: ΔT = Desired temp - Incoming water temp. Measure incoming temp or use local average (typically 50-60°F).

Q5: How does this relate to tank size?
A: Tank size determines how long heat can be delivered at this rate. Continuous systems need sufficient BTU input.