Efficiency of Nat Gas Steam Boiler

Kjmass1

I have a 1950's Pennco natural gas boiler, I believe 155k btu. One of your pros from this site helped tune it up as it had been neglected with the prior owner.

As of right now it seems to be running great. I was wondering if there is a way I can test efficiency? MA has a $2k rebate to upgrade and I was wondering what the return would be on a newer 84% efficient boiler.

Any way I could figure this out on my own?

Thanks

BobC

What is the efficiency of that old boiler? What did the pro think about it's condition?

You will have to install a chimney liner with a new boiler if you don't already have one - they don't give them away.

If the old boiler is 70% efficient then your savings would be 14% of your fuel bill, if it's 60% your savings would be 24% of your fuel bill. If it were 70% efficient AND still in good shape you might be better off using the money to upgrade the building it's in.

That old boiler is going to be replaced at some point, make sure your the one who decides when it's in your best interests to do that. Make sure the contractor knows what he is doing, a bargain price on the install isn't worth it if it's not installed correctly.

Bob

Kjmass1

Thanks Bob. The plumber thought it was best to keep it for the winter after putting some $$ in to it. It will be our first winter in the house after doing a lot of construction and insulation improvements.

Is the time it takes to make steam from a cold start an indicator off its health? Or the time it takes to travel to the end of the mains on a warm start?

j a_2

Where does it sat you have to installer a chimney liner , going gas to gas…..

Eric_32

This is what the MA Plumbing board has to say:
http://www.mass.gov/ocabr/docs/dpl/boards/pl/exception-to-lining-an-existing-chimney.pdf

j a_2

That was my point, no need for a liner if you fall under the guidelines…..Nice post Eric

Kjmass1

So I was reading that that you can determine the efficiency of your boiler when it was put in to production by dividing the input by output. So roughly 192k/153k puts it at 78% when it was new. I imagine that has decreased over the years but it is a good baseline. Decades later we're barely at 84% but that is physics I guess.

John Mills_5

Remember that the 78% figure was a steady state figure. That is totally different than AFUE used on today's boiler. Odds are something from the 50s has an ANNUAL efficiency of 60% or worse. Annual efficiency looks at how much heat is lost on the warm up of the boiler plus how much is lost on cool down plus up the flue during off cycle. With steam you are limited to mid 80s for AFUE.

With hot water you can get up to about 85% AFUE on a non condensing boiler, beyond that you would need a condensing boiler and the AFUE continues and varies based on water temp. Usually if you have water temp above about 140° you are not condensing and your AFUE is close to that of the standard boiler.

Of course AFUE assumes proper sizing too. If you have an oversized boiler constantly cycling, real world annual efficiency will be well lower than the rating. Like a driver driving his car aggressively won't get the rated MPG either.

Kjmass1

Thanks! That is very helpful. Someone came out to look at it for possible replacement and they thought it was a 1970's model...so hopefully it is a little more efficient than that.