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BTU/hr Formula:
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The BTU/hr calculation determines the required heating capacity for a natural gas tankless water heater based on flow rate and desired temperature rise. Proper sizing ensures adequate hot water supply for your needs.
The calculator uses the formula:
Where:
Explanation: This formula calculates the British Thermal Units per hour required to heat water at a specific flow rate by the desired temperature difference.
Details: Correctly sizing your tankless water heater is crucial for ensuring adequate hot water supply, energy efficiency, and preventing system overload. Undersized units cannot meet demand, while oversized units waste energy and money.
Tips: Enter the required flow rate in GPM and the desired temperature rise in °F. Consider peak usage times and multiple fixture usage when determining your GPM requirements.
Q1: What factors affect GPM requirements?
A: The number of bathrooms, fixtures running simultaneously, and typical usage patterns all affect your GPM requirements.
Q2: How do I determine the temperature rise needed?
A: Subtract your incoming groundwater temperature from your desired output temperature. Typical groundwater temperatures range from 40-70°F depending on climate and season.
Q3: What is a typical GPM requirement for a household?
A: Most households require 5-10 GPM depending on the number of bathrooms and simultaneous hot water usage.
Q4: Can I use this for electric tankless water heaters?
A: While the basic principle is similar, electric units use different calculations (kW instead of BTU/hr) and have different efficiency considerations.
Q5: Should I add a safety margin to the calculated BTU/hr?
A: It's recommended to add 10-20% safety margin to account for peak demand, future needs, and efficiency variations.