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Some questions on real fuel usage calculations

iainb | Posted in Mechanicals on

I have some questions on the Dana Dorsett article using real fuel consumption to measure heat load.

I have two factors running the calculation. The first is that my boiler is an oil burner retrofitted to burn gas. The original boiler seems to have been a 151,000 input and 131,000 out (funnily enough it looks like the same Weil-McClean in the article). When I looked at the guide on the replacement burner  they seem to have tuned it to the same 151,000 BTU input as the original.

Am I able to just use the numbers on the boiler to calculate efficiency? Or do I need to do some additional measurements?

My other issue sounds crazy. I keep the thermostat at 68 most of the time, but the house has wildly varying temperatures. Upstairs bedrooms can be 10 degree hotter and the kitchen 6-8 degrees colder (I’ve got some airsealing to do.)

Can I just use the 68 degree temperature when the real temp is that all over the place?


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  1. iainb | | #1

    I'm going to bump this backup hoping someone can suggest an answer. The efficiency part is especially vexing.

  2. paul_wiedefeld | | #2

    The efficiency part is easy - a non-condensing gas boiler maxes out at about 80% efficiency. So no more than that, probably lower in practice.

    1. iainb | | #3

      Awesome, thank you.

      This thing is oversized by what looks like at least 2x.... yikes.

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