1. What is a Tankless Water Heater Size Calculator?

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

Purpose: It helps homeowners and plumbers select properly sized tankless water heaters for efficient hot water delivery.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( S \) — Heater size (kW)
• \( F \) — Flow rate (gallons per minute)
• \( T \) — Temperature rise (°F)
• \( 8.33 \) — Constant (lbs per gallon of water × minutes in hour ÷ BTU to kW conversion)

Explanation: The formula calculates the energy required to heat water at a given flow rate through a specified temperature increase.

3. Importance of Proper Sizing

Details: Correct sizing ensures adequate hot water supply, energy efficiency, and prevents overworking the unit.

4. Using the Calculator

Tips: Enter the maximum flow rate needed (sum of all fixtures that might run simultaneously) and the desired temperature rise (difference between incoming water and desired output). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical temperature rise for showers?
A: Most showers need a 45-60°F rise depending on incoming water temperature and desired shower temperature.

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

Q3: What if my calculated size is between standard unit sizes?
A: Always round up to the next available size to ensure adequate capacity.

Q4: Does this account for cold climate water temperatures?
A: No, adjust your temperature rise based on your local groundwater temperatures (typically 40-50°F in winter).

Q5: Should I add a safety factor?
A: Consider adding 10-20% to the calculated size for peak demand periods.