Calculate BTU Output of Gas Water Heater: Formula & Tips | 475°F Exhaust

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Discussion Overview

The discussion revolves around calculating the BTU output of a gas water heater based on the exhaust temperature of 475°F and the diameter of the flue. Participants explore various methods for estimating BTU output, including theoretical formulas and experimental approaches.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about a formula to calculate BTU output based solely on the exhaust temperature and flue diameter.
  • Another participant argues that it is not possible to calculate BTU output from the exhaust temperature alone and suggests reading the gas meter during operation or checking the nameplate for information.
  • A different approach is proposed involving an experimental method where one could measure the temperature increase of water placed near the exhaust to estimate BTU output, emphasizing the need to measure both the temperature change and the amount of water used.
  • One participant acknowledges the experimental method as a way to estimate the heater's power but notes it may only provide a rough approximation.
  • Another participant suggests contacting the manufacturer for more accurate information, reiterating the limitations of the available data.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of calculating BTU output from the given information. There is no consensus on a definitive method, and multiple approaches are discussed without resolution.

Contextual Notes

Participants highlight limitations in the available data, including the reliance on exhaust temperature and flue diameter, and the potential need for additional measurements or manufacturer specifications to achieve accurate calculations.

attitudeworks
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I have a gas water heater that has an exhaust of 475 degrees Fahrenheit. I would like to know, what formula can I use to determine the amount of BTU's that the water heater produces (or wastes) per hour of use. I only have the temperature of the exhaust (475 Deg. F) and the diameter of the flue which is 3". I would appreciate any help or guidance. Thank you.
 
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You can't calculate it from the exhaust temp. But You can read your gas meter a couple of times when it us running. Or read it off the nameplate...
 
Last edited:
You could do an experiment . A BTU is the amount of heat needed to raise one pound of water one degree F . You could place a glass jug of water near the exhaust and measure the temp increase . And of course measure the amount of water . Or you could
do it in calories , then convert to joules and then divide by the amount of time it took so this will give you power .
At least this would give a crude approximation .
 
@ cragar: it is a great method to estimate the heater's power within three orders of magnitude.

@attitudeworks: it is impossible to tell using only this information. Can't you contact the company?
 

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