I've received news that I'll need to get a new boiler. My wife and I want to take this opportunity to switch to natural gas from oil. I'm a technical guy, but I'm having trouble deciphering the power output of my current boiler to size a replacement.

I'm looking for a useful calculator to convert from steam volume output, to BTUs. This is merely as a budgetary exercise for information when a contractor comes to provide an estimate.

Any recommendations?

  • So what is the power output of your current boiler, with the appropriate units (BTU?)?
    – AWMoore
    Commented Mar 24, 2011 at 14:24
  • That's the problem. The boiler lists the output in a number of different units of steam produced, not in BTUs.
    – Spencer K
    Commented Mar 28, 2011 at 16:15

3 Answers 3


instead of sizing your current boiler, i would instead have a heating professional visit your home and calculate the heating requirements of your home from scratch.

  • 2
    We're also making the same change from oil to gas. This is the right advice -- have your HVAC contractor visit and do a "heat loss calculation" -- an estimate of what heat output will be required to keep your house warm on the coldest day of the year in your climate, based on the size of your house, number of windows, types of insulation, etc. For efficiency, you'll want the minimal size that can keep your house warm, with perhaps a little extra in case you build an addition. :) Commented Mar 25, 2011 at 23:09
  • I'm doing this merely as a budgetary exercise, and see what prices are out there. I already have a number of contractors scheduled, but I like to be as well informed as I can before they do their estimates.
    – Spencer K
    Commented Mar 28, 2011 at 16:16

I'm in the same boat. One helpful resource I found was this:


It gives you the various conversions of units based on BTUs. If your gas is measured in therms, you can convert the number of gallons of oil to therms by multiplying them by 0.721.

There is also http://www.peco.com/pecowebsite/peco/html/oil.htm which I found to give me a savings estimate pretty close to what I calculated myself based on actual oil and gas bills from the last 5 years.

Overall I agree with the other suggestions though: get a pro to come out and tell you what to get. There is a lot of labor involved too: probably you are going to want to have your existing oil tank removed if it's above ground.


I found this calculator, which also provides units of conversion. http://www.cbboilers.com/scc/BoilerSteamCostCalculator.html

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