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# Calculating efficiency of older boilers

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Member Posts: 3
I am trying to find some information on calculating the efficiency of older style gas hot water boilers. I was wondering if there are a set of equations or some software that would be helpful. Thanks.

• Member Posts: 1,935
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easy on paper

clock the gas meter.

measure delta T water temp. in/out of boiler

measure flow rate of water.in/out of boiler

delt T x 8.33 x gallons flow = btu's boiler output

meter clocking will give you btu's into the boiler
• Member Posts: 67
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don't forget you have to multiply gpm times 60 minutes for the BTUH.
• Member Posts: 12
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estimating efficiency

If you don't have access to temp in and temp out, or flow rate in & flow rate out, one way to *estimate* efficiency of an old boiler is to take a combustion efficiency test result and multiply by 0.85. So if a technician performs a combustion efficiency test and says the boiler has a combustion efficiency of 84%, then the overall efficiency (similar to AFUE) is about 71% (85% x 0.85). This would account for off-cycle losses, and so forth. Of course, this requires a combustion efficiency test to begin with.
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Okay.....

How do you factor in whether it has a vent damper; or electronic ignition?

How do you account for a boiler with a circulator post purge cycle? With 3" of insulation vs. 1" of insulation?

Where did this formula come from?

Noel
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