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

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In summary, there is no direct formula to determine the BTU's of a gas water heater based on the exhaust temperature and flue diameter. Some suggestions include reading the gas meter or nameplate, conducting an experiment with water temperature increase, or converting to joules. However, these methods may only provide a rough estimate. It may be best to contact the company for more accurate information.
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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...
 
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  • #3
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 .
 
  • #4
@ 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?
 
  • #5


To calculate the BTU output of a gas water heater, you will need to use the following formula:

BTU Output = (CFM x Delta T x 1.08) / Efficiency

CFM = cubic feet per minute of exhaust flow
Delta T = difference between exhaust temperature and ambient temperature (in this case, 475°F - ambient temperature)
1.08 = constant for specific heat of air
Efficiency = efficiency of the water heater, typically expressed as a percentage (e.g. 80% = 0.80)

In order to solve for the CFM, you will also need to know the cross-sectional area of the flue, which can be calculated using the diameter (3 inches) and the formula for the area of a circle (A = πr^2).

Once you have all of these values, you can plug them into the formula to calculate the BTU output of your gas water heater. Keep in mind that this calculation will only provide an estimate, as there may be other factors that can affect the actual BTU output of the water heater. It is always best to consult the manufacturer's specifications for the most accurate information.
 

1. How do I calculate BTU?

BTU, or British Thermal Unit, is a unit of energy commonly used in the heating and cooling industry. To calculate BTU, you will need to know the specific heat capacity of the material, the change in temperature, and the mass of the material. The formula for calculating BTU is: BTU = specific heat capacity x mass x temperature change.

2. What is specific heat capacity?

Specific heat capacity is the amount of energy required to raise the temperature of one unit of mass of a substance by one degree Celsius. It is usually measured in joules per gram per degree Celsius (J/g°C) or calories per gram per degree Celsius (cal/g°C).

3. How do I determine the mass of the material?

The mass of the material can be determined by weighing it using a scale. Make sure to use the appropriate units for mass, such as grams or kilograms, depending on the size of the material.

4. How do I measure the change in temperature?

The change in temperature can be measured using a thermometer. Place the thermometer in the material and wait until it reaches thermal equilibrium, then record the temperature. Next, heat or cool the material and record the final temperature. The change in temperature is the difference between the initial and final temperatures.

5. Can I use BTU to calculate the energy needed for heating or cooling my home?

Yes, BTU can be used to calculate the energy needed for heating or cooling your home. However, other factors such as insulation, climate, and efficiency of your heating and cooling system should also be taken into account when determining the appropriate size and capacity of your system.

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