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

Definition: This calculator determines the required size (in BTU/hr) of a tankless water heater based on your desired flow rate (GPM) and temperature rise needed.

Purpose: It helps homeowners and plumbers properly size tankless water heaters to ensure adequate hot water supply for all fixtures.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( Size \) — Heater capacity (BTU/hour)
• \( GPM \) — Required flow rate (gallons per minute)
• \( \Delta T \) — Temperature rise needed (°F)
• \( 2 \) — Conversion factor (500 BTU per GPM per °F × 4 minutes)

Explanation: The formula accounts for the energy needed to heat each gallon of water by the desired temperature increase.

3. Importance of Proper Sizing

Details: Correct sizing ensures you get enough hot water when needed without overspending on an unnecessarily large unit.

4. Using the Calculator

Tips:

• Add up the flow rates of all fixtures that might run simultaneously
• Typical temperature rise is 70°F (from 50°F groundwater to 120°F output)
• For colder climates, you may need a higher temperature rise

5. Frequently Asked Questions (FAQ)

Q1: What's a typical GPM requirement for a home?
A: A standard home might need 7-10 GPM, but this depends on the number of bathrooms and appliances.

Q2: How do I determine my required GPM?
A: Add up the flow rates of all fixtures that might run simultaneously (shower: 2.5 GPM, faucet: 1.5 GPM, etc.).

Q3: Why is temperature rise important?
A: The colder your incoming water, the more energy needed to heat it to your desired temperature.

Q4: What if my calculated size is between standard models?
A: Always round up to the next available size to ensure adequate capacity.

Q5: Does this account for elevation or hard water?
A: No, for high elevations or very hard water, you may need to increase the calculated size by 10-20%.