AFUE for Amer Std G-2?

Pat Justis

I have an older American Standard G-2 but do not have the date on the unit. Here are the numbers I find on it:
150,000/120,000 and L2-G26 DG.
Can anyone help me estimate my AFUE?
Thanks

Mike T., Swampeast MO

Assuming 150,000 BTUs of heat energy in versus 120,000 BTUs available for heating (e.g. some measure of "heating capacity") you have 80% efficiency. Most cast iron, atmospheric boilers have similar gross efficiency ratings. American Standard boilers were among the finest. AFUE didn't exist then, but it would likely be quite close to 80.

Note that "heating capacity", AFUE, I=B=R, etc. are estimates based on extremely simplified situations that have little to do with reality.

Once the boiler is installed in a real system in a real structure in the real world, a host of factors begin robbing efficiency. Most of the time, your system efficiency will be WAY below that of the boiler itself.

That's not a problem when all boilers operate similarly. In that case you can compare AFUE or other ratings to get a reasonable estimate of comparative efficiency.

If you look up modern cast iron atmospheric boilers (what your American Standard is considered) you'll find that efficiency ratings have not changed much. The heat exchangers have gotten a bit smaller and hold less water--that allows the boiler itself to be a bit more responsive and such will show as a slightly increased boiler efficiency. Standing pilots are frequently replaced with some form of electronic ignition. Most or all now have an automatic flue damper. These measures allow a bit higher boiler efficiency and you'll find AFUE in the very low 80s. Note that while the vent dampers are fail-safe, fail they do and often rapidly. The electronic ignition systems are often replaced with standing pilots. After a decade of service, the system efficiency is likely just about what you have now.

Condensing and particularly condensing/modulating boilers address some of the SYSTEM inefficiencies that are not considered by ratings. The AFUE difference between these boilers and ones like yours is no longer a valid comparison. In most cases, condensing/modulating boilers achieve SYSTEM efficiencies MUCH GREATER than the difference in AFUE. You'll find that just like with most simple cast iron boilers there is little difference in the AFUE between condensing and especially condensing/modulating boilers. Just don't try to compare them (via AFUE) to ones of another class!

p.s. There are some "special" cast iron boilers out there that achieve significantly higher efficiency than the norm. There aren't many however and it's very difficult to compare them (via AFUE) to any others.
They'll be somewhat better than the AFUE difference would lead you to believe, but not so much so as the ones that condense and modulate.

Steamhead

Pat, Mike has a real good point

you can lose efficiency either at the boiler or out in the system. The boiler should be tested with a digital analyzer to ascertain combustion efficiency and to be sure it's not generating carbon monoxide. We didn't have digital analyzers when your boiler was made, but you'll probably find yours runs with decent efficiency.

As for the system, I'd need to know if you have a steam or hot-water system to make suggestions.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"