Boiler Sizing

scrook

It's a steam system so he's gotta size the boiler to the radiation installed not to the heat loss of the structure as he would for a hot water system.

Chris NJ_2

Boiler Sizing

I am getting bids on replacing my 30 year steam boiler. So here are the house specs: 1922 Center Hall with 3600 SF of living space, original construction (no insulation except in attic) 543 SF of radiation on a single pipe system and a 2.5" 96 foot single loop delivery. Contractor wants to put in a Weil Mclain EG-55. However, my calculation of Steam SF with a pick up factor of 1.33 is something that should be capable of around 720 SF of steam, not the 508 this model produces. Is this undersized for the house? Should I go back and tell him it won't work? Help please???

Chris Maderia

How

about a heat loss wouldn't that be the best and correct way to size the boiler? The sqft of exisiting radiators is irrelevant to what the structures heat loss is. Do yourself a favor, get a heat loss.

hot_rod

Chris, this is steam

He is on the right path. If you size it to the heat load, but keep the same radiation, some radiators may not get steam. If the boiler is too small, the fuel cost will be through the roof!

Noel

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Howard

"He is on the right path" You mean Chris NJ, right? I concur. Sounds like the contractor sized for the building, not the radiation.

Howard Service Technician Extraordinaire

Mark Hunt

Steam Boiler Sizing

Chris, If you are doing strictly a boiler replacement with no modifications to the system, you must measure every radiator in the house. Weil Mclain has a nice little booklet with the square footage of different radiators in it. You must size the boiler so it matches the connected load. If you size it using a heatloss calc, you will as hot rod said, not be able to fill all the radiators with steam. No doubt there have been upgrades made to the home(insulation, windows, air sealing, etc.)that will have made big differences in what the heat loss was then compared to now.

Terry O

steam boiler sizing

Sizing a replacement steam boiler follows a simple princple. Boiler capacity = Radiation load. NOT heatloss. In undersized boiler systems, steam condenses as fast as the boiler generates it, never making it to the system extremeities = dissatisfied customer + call back(s). This has been taken from my notes of steam boiler sizing recently taken at a steam seminar conducted at the Utica boiler plant by Carl Saunders, training director, and poorly attended by (3)THREE trade professionals. Some of us youngsters (I'm 47 with 28 years in the business) may not have the years of field experience, but attending a seminar such as this is always helpful in providing accurate info. (IMHO) Chris(NJ) you're concerns are right on.

Chris NJ_2

More info

Thanks for the responses guys. To clear up some things, (1) I am not sizing to heat loss (but think contractor is); (2) no modifications since 1922 except insulation in attic (original mahogany windows, no insulation in walls, etc.). Point of reference: the original coal fired boiler in the house was a Richardson capable of 1200 SF of steam. That one was replaced in 1972 with the current boiler.

Now, if I use Dan H.'s formula in Lost Art, the 543 SF of existing radiation using a pickup factor of 1.5x and converting to BTU's equals 195,480 BTU/hr. This would equate to Weil Mclain unit EG-65 (203,000 BTU/Hr). This unit is capable of 633 SF of steam. But if I use the existing radiation of 543 SF and a pickup factor of 1.3 then I need something in the area of 720 SF even though the BTUs/hr is correct. Which one is more accurate in boiler selection, BTU/Hr or SF of steam?

I think the EG-55 the contractor wants to install is undersized for this load.

Unknown

RE: Boiler Sizing

Chris NJ,

I think the one thing that everyone is missing here is that most of the boiler manufacturers rate their steam boilers by Square Feet of Steam by IBR Net Rating standards. These Net Ratings already incorporate a 33% pickup loss. Unless there are some enormous pipes and extemely long runs, there is in most cases no need to size the boiler any larger than the connected load. Hope this helps.

Glenn Stanton

Manager of Training

Burnham Corp.

steve_6

boiler sizing

What do you consider enourmous or extremly long piping? Dan's lost art book suggests that the 1.33 pick up factor may not be enough especially for a turn of the century, 2 pipe vapor system. Please explain?
Thanks

steve_6

sizing

The EG55 is undersized for your radiation load. It is rated to handle up to 508 sq. ft. of radiation with an allowance of 1.333 already figured in. You might want to consider another contractor.

Unknown

I would consider

piping that may have originally sized for much more radiation than is presently installed to be enormous. We see this occasionally in systems that have been divided up for rental reasons and the old pipes remained with plugs in the old tees. Also piping that in not insulated going through a cold crawl space. It is a common sense thing that may differ with each job. Hope this helps.

Glenn

Dave_23

Weil-McClain booklet

How can I get a copy of the WM radiator sizing booklet mentioned above?

Thanks, Dave

steve_6

WM literature

you can go to their web sight