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Electric Tankless Water Heater Sizing Formula:
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Electric tankless water heater sizing determines the appropriate power rating (in kW) needed to heat water to the desired temperature based on flow rate and temperature rise. Proper sizing ensures adequate hot water supply while maintaining energy efficiency.
The calculator uses the electric tankless water heater sizing formula:
Where:
Explanation: The formula calculates the required heating power by multiplying the flow rate by the temperature difference and a conversion factor that accounts for the specific heat of water and unit conversions.
Details: Correct sizing is crucial for ensuring sufficient hot water supply, preventing energy waste, and extending the lifespan of the water heater. Undersized units may not provide enough hot water, while oversized units waste energy and increase costs.
Tips: Enter the desired flow rate in gallons per minute and the required temperature rise in degrees Fahrenheit. The temperature rise is the difference between your desired output temperature and the incoming water temperature.
Q1: What is temperature rise (ΔT)?
A: Temperature rise is the difference between your desired hot water temperature and the temperature of the incoming cold water. For example, if you want 120°F water and your incoming water is 50°F, the temperature rise is 70°F.
Q2: How do I determine my flow rate?
A: Add up the flow rates of all fixtures that might run simultaneously. Standard flow rates: shower (2.5 GPM), kitchen faucet (2.2 GPM), bathroom faucet (1.5 GPM).
Q3: What if I have multiple bathrooms?
A: Calculate the total simultaneous flow by adding the flow rates of all fixtures that might be used at the same time. For two showers running simultaneously, you would need at least 5 GPM capacity.
Q4: Are there other factors to consider?
A: Yes, consider your electrical service capacity, voltage requirements (most electric tankless heaters require 240V), and local climate (colder incoming water temperatures require more heating power).
Q5: Should I add a safety margin?
A: It's recommended to add 10-20% to the calculated kW to account for variations in water temperature and flow rates, and to ensure adequate performance during peak demand.