Boiler Sizing

Tony1

Hi all,

Hope you can help here. I've done much reading about steam heat (Dan is amazing). My old steam boiler ran dry due to a faulty low water cut-off (M&D series 67), cracked and is now leaking. I contacted two of the "best" professional plumbers in the area who "know" steam well. My cracked boiler is a Burnham with a net steam output of 447 sq ft. (I have attached an image of the specs).

I have two floors with recessed cast iron radiators which have a total of 122 sections. Converting that to (122 x 2.25) 275 EDR.

The basement calculates to about a heat loss 8,000 BTU/Hr and is heated by aluminum baseboard. From my knowledge, gained from these forums, that should not be added as it will be part of the p/u factor. I am looking at a Williamson boiler and assumed I would need a GSA-125 rated at net sq ft steam of 325.

Plumber #1 came and looked at the job, told me he will get back to me with the proper size. He got back to me that I can use a GSA-150 (sq/ft 392) but better go with a GSA-175 (sq/ft 454) as this is "what you had".

Plumber #2 called me that he discussed it with the "expert" at the supply and told me I need a GSA-250 (sq/ft 654)! When I questioned him he told me to speak to the expert. I went down to the supply house and asked him how he got to these numbers. He told me that he started with the EDR of 275 the added 100 for the risers so that's 375, now, "as a rule", he adds 33% for heat loss, and in addition, he added for the basement baseboard. Therefore he thinks I need at least a GSA-250. When I started challenging him, he told me "seems you know more about this than I do, so do as you think" (And this is the expert!!).

It is getting cold here and I need to start the job asap, I am not confident enough to argue with all these "experts". I would appreciate your thoughts and reassurance.

Thank you all!

Fred

You need a boiler that is as close to that 275 EDR as you can get. Everything they are proposing is way oversized. If I were you, I'd not use any of these guys. They clearly do not know what they are doing, as it relates to steam. Go to the "Find a Contractor" tab at the top of this page and plug in your Zip Code. Some excellent Steam Pros here.
Back to your boiler, The replacement boiler will have a plate on it, just like your old one. Match that Sq. Ft. of steam to your calculated radiator EDR. That number, on the plate already factors in the 33% piping and Pick up factor (output over and above the number on that plate).

ChrisJ

If it was my system I'd do a GSA-100.
The GSA-125 would be what most would install. Anything bigger is unacceptable.

KC_Jones

Tony1 said:

Plumber #1 came and looked at the job, told me he will get back to me with the proper size. He got back to me that I can use a GSA-150 (sq/ft 392) but better go with a GSA-175 (sq/ft 454) as this is "what you had".

Plumber #2 called me that he discussed it with the "expert" at the supply and told me I need a GSA-250 (sq/ft 654)! When I questioned him he told me to speak to the expert. I went down to the supply house and asked him how he got to these numbers. He told me that he started with the EDR of 275 the added 100 for the risers so that's 375, now, "as a rule", he adds 33% for heat loss, and in addition, he added for the basement baseboard. Therefore he thinks I need at least a GSA-250. When I started challenging him, he told me "seems you know more about this than I do, so do as you think" (And this is the expert!!).

You take the EDR calculation and compare it directly to the boiler manufacturers ratings, it's really that simple add nothing, don't round up, don't add any "just in case".

The first guy is crazy.
The second needs to quit his job. He is not an expert and should not be referred to as such. Feel free to send all these people to this website for re education.

Where are you located? We may know a competent contractor in your area.

Tony1

Thank you! I'm in NYC.

Dave0176

I would install the GSA 100,000 or Weil McLain EG35. These boilers put out 258 sq ft steam and 343 when you add the 1.33 pickup factor. You need 66,000 btu of radiation and 8000 btu of pickup totaling 74,000 btu the EG35 is rated for 83,000 output. You will be fine.