down sizing an old steam system

Paul_11

You said,

"An over-sized boiler is not as efficient, but the loss of efficiency is not that great until you are double or more".

I agree that going a little bigger than your numbers tell you so you can sleep at night is a good practice, but I don't agree with what you said. I especially carebul when installing a gas atmospheric boiler, because here in NYC we can't get the required gas pressure so we can't get the boilers to fire at it rated capacity without replacing the gas train.
When I replace a steam boiler, 90% of the time I find the old one was two times up to three times bigger than the new one. I take some pride in this. And my customers tell me their bills are significanly less. I had one customer recently that said they used about half the oil the year after we did the job.



Respectfully,

Paul B. Shay
pshay@arealgoodplumber.com
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LMFS 654B
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Art_6

I have replacement steam boiler to quote. I want to reduce the boiler size. The Old Boiler is 1964 Burnham Model 750 series #1 with Vapor Controls. Old Boiler Ratings: Max firing rate 9.30 GPH, Square Foot of radiation rating is 3000.
Boiler has been heating this building for many years with the burner locked in low fire. Approximatly 3.10 GPH.
The Buildings has 2446 square feet radiation. If we can heat this building with 3-3.5 GPH I know I do not need an other 9 GPH boiler. But I am not real comfortable quoting a boiler with a square foor capasity so much below the total square footage of what is in the building. I was looking for some guidence on down sizing.
If needed I can go back and measure this building for a heat loss calculation, but I was thinking we may have what we need right here.

[Deleted User]

I would size

the boiler to the radiation load. Spec a good lo-hi-lo burner. Add a vaporstat to drop to low fire. Let her go up & down as load dictates.

[Deleted User]

I would size

the boiler to the radiation load. Spec a good lo-hi-lo burner. Add a vaporstat to drop to low fire. Let her go up & down as load dictates.

[Deleted User]

I would size

the boiler to the radiation load. Spec a good lo-hi-lo burner. Add a vaporstat to drop to low fire. Let her go up & down as load dictates.

Patrick Linhardt, \"Linhardt's Field Guide to Ste

other things to consider

It is generally good practice to size a replacement steam boiler to the connected load. If you measured all the radiation, then you can use that to compare to the new boiler's net square foot rating. Be sure to count any un-insulated supply piping as radiation.

Things to consider to go over the connected load:
1) piping that runs through un-heated areas
2) quick pick-up requirements

Things to consider to go under the connected load:
1) over-sized radiation for the heat loss. Be careful with this, the system has to be well balanced on the supply side with TRV's, orifices or metered supply valves(which are sometimes found on vapor systems).

3.25 GPH = 455,000 btu input
455,000 x .85 = 386,750 btu gross output
386,750 x .67 = 259,122 btu net
259,122 / 240 = 1080 sq. ft.

I'd run the heat loss. But size it so you can sleep at night. An over-sized boiler is not as efficient, but the loss of efficiency is not that geat until you are double or more.

Best regards, Pat

Patrick Linhardt, \"Linhardt's Field Guide to Ste

yes and no

Hi Paul,

What I'm referring to is a government study that I saw years ago comparing new boilers of varying degrees of oversizing in the same installation. What you and your customers are experiencing, and people all over the country for that matter, is the improvement of efficiency from the old boiler to the new boiler. The old boiler was not as efficient by design when it was made, and efficiency generally declines with age because of accumulation of junk in the bottom of the boiler retarding heat transfer.

I agree 100% with you that proper sizing is a service we should perform on any steam installation and that most boilers are oversized. Proper sizing saves money on the intial purchase and for years to come. However, the savings are more from modern efficiencies vs. older efficiencies and equipment "age".

I'm going today to measure a house to get a boiler sized for a contractor. The rating tag is there, but who knows the circumstances when it was replaced. Was it the only one available? Did the owner insist on a larger boiler? Did the last contractor just go with the last size, or step across the street and hold up fingers?

It sounds like you are doing a great job for your customers, keep up the good work.

Best regards, Pat