1. What is a Tankless Hot Water Heater Sizing Calculator?

Definition: This calculator determines the required kilowatt (kW) rating for a tankless water heater based on flow rate and desired temperature rise.

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:

• \( kW \) — Required heater power (kilowatts)
• \( GPM \) — Flow rate (gallons per minute)
• \( \Delta T \) — Temperature rise needed (°F)
• 2.4 — Conversion factor (accounts for water's specific heat)

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

3. Importance of Proper Sizing

Details: Correct sizing prevents undersized units (that can't meet demand) and oversized units (that waste energy and cost more).

4. Using the Calculator

Tips:

• Measure your actual flow rate at fixtures
• Calculate ΔT as desired output temp minus incoming water temp
• For multiple fixtures, sum their flow rates

5. Frequently Asked Questions (FAQ)

Q1: What's a typical temperature rise?
A: For showering: 60-70°F (from 50°F groundwater to 110-120°F). Adjust based on your climate and preferences.

Q2: How do I measure my flow rate?
A: Time how long it takes to fill a 1-gallon container at your faucet (60 seconds = 1 GPM).

Q3: What if I need to run multiple fixtures?
A: Add all simultaneous GPM needs (e.g., shower + sink = 2.5 + 1.0 = 3.5 GPM total).

Q4: Why is the conversion factor 2.4?
A: It combines water's specific heat (8.33 lb/gal × 1 BTU/lb-°F) and unit conversions (3.412 BTU/hr per watt).

Q5: Should I add a safety factor?
A: Consider adding 10-20% to the calculated kW for peak demand and future needs.