1. What is a Tankless Water Heater Size Calculator?

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

Purpose: It helps homeowners and plumbers properly size tankless water heaters for efficient and adequate hot water supply.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• Size — Required heater capacity (BTU/h)
• Max GPM — Maximum flow rate needed (gallons per minute)
• ΔT — Temperature rise required (°F)
• 500 — Conversion factor (BTU/h per GPM per °F)

Explanation: The formula calculates the energy needed to heat water at your desired flow rate through the required temperature increase.

3. Importance of Proper Sizing

Details: Correct sizing ensures sufficient hot water supply while maximizing energy efficiency and preventing undersized or oversized units.

4. Using the Calculator

Tips:

• Determine your peak hot water demand in GPM
• Calculate ΔT as the difference between incoming water temperature and desired output temperature
• Typical ΔT values range from 40°F to 70°F depending on climate and usage

5. Frequently Asked Questions (FAQ)

Q1: What is ΔT (delta T)?
A: It's the temperature rise needed - the difference between your incoming water temperature and desired output temperature.

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

Q3: What's the 500 factor in the formula?
A: It's the approximate number of BTUs needed to raise 1 gallon of water by 1°F in one hour (8.33 lbs × 60 min).

Q4: Should I add a safety factor?
A: It's recommended to add 10-20% to the calculated size for peak demand periods.

Q5: What if my water is very cold?
A: In colder climates with low incoming water temps, you'll need a higher ΔT and thus a larger heater.