1. What is a Tankless Water Heater Capacity Calculator?

Definition: This calculator determines the flow rate (in gallons per minute) that a tankless water heater can deliver based on its BTU rating and the desired temperature rise.

Purpose: It helps homeowners and plumbers size tankless water heaters properly for different applications and climate conditions.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( GPM \) — Flow rate in gallons per minute
• \( BTU/h \) — Heater capacity in British Thermal Units per hour
• \( \Delta T \) — Temperature rise in degrees Fahrenheit

Explanation: The formula calculates how many gallons of water per minute can be heated by a given BTU input for a specified temperature increase.

3. Importance of Proper Sizing

Details: Correctly sizing a tankless water heater ensures adequate hot water supply for simultaneous fixtures while maintaining energy efficiency.

4. Using the Calculator

Tips: Enter the heater's BTU rating and desired temperature rise (difference between incoming water temperature and desired output temperature). Default ΔT is 70°F (typical for raising 50°F groundwater to 120°F).

5. Frequently Asked Questions (FAQ)

Q1: What's the 500 constant in the formula?
A: It's a conversion factor accounting for water's specific heat (8.33 lb/gal × 60 min/h ÷ 1 BTU/lb-°F ≈ 500).

Q2: What's a typical temperature rise for showers?
A: Most showers need about 70°F rise (from 50°F groundwater to 120°F shower temperature).

Q3: How do I find my groundwater temperature?
A: Check local water authority data or use 50°F as a safe estimate for most regions.

Q4: What flow rate do I need for a shower?
A: Standard showers need 1.5-2.5 GPM, while rain showers may need 2.5-4 GPM.

Q5: Why does my tankless heater perform below rating?
A: Mineral buildup, undersized gas lines, or higher-than-expected groundwater temps can reduce performance.