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Boiler Size Confusion--EDR vs Output

out of Vaporstats at that time :-(

But that particular Pressuretrol works fairly well, and it's on a brass pigtail.


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  • I am confused about how to get my new boiler (steam going out chimney) properly sized.
    "Inherited" a 1970 Dunkirk (through Sears), 225,000 BTU input, alleged 180K output. I had always thought this might be oversized.
    My heating man is ordering the 207K input Crown (we are in Philadelphia suburbs, Crown is the easiest to ontain since it's one of the few industrial manufacturers left here!).
    With some time on my hands, I was finally able to do the research and measure my radiation, most of my rads are wall units using the same base piece.
    Going through my house, I have come up with about 415 square feet of radiators, not counting 3 convectors that I can't figure. They are radiators only, no additional back part. My piping seems to be about 130-140 square feet, going through the basement, measuring lengths, and applying the math.

    Here's where I am confused. This comes up to I=B=R of at least 550 square feet, not including those 3 convectors. The Crown specs say that its output is 533 square feet.
    However, the Crown's rated OUTPUT is 171,000 BTU. This figure divided buy 240 dgrees, would mean it can do 712 square feet, which would be more than enough even after adding the uncounted convectors (or, 533 time 240 = 128,000 BTU). And I have noticed this on everyone's ratings, that I=B=R the square feet times 240 is well less than the rated output. I also noticed that some of these manufacturers specify to include the 1.33 pick-up in calculating the need.

    So which is it? Which is the spec that I need to be following here? I want to make sure that I do not size this unit wrong. Can anyone explain this, or explain what I am missing here?
  • The difference

    between the DOE output and the Net ratings in EDR or BTU/hour is that the latter includes the pick-up factor. This means that if your system has, say, 450 square feet, you don't need a boiler with any higher Net rating than that unless there is some overriding reason such as piping that is oversized or more extensive than usual.

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  • Got It

    Thanks, Steamhead. I had just now figured out the same after a careful re-reading of some passages and combining them, and it is good to have this confirmed.
    I think my radiator square footage is about 485 feet, using a chart I saw at Burnham for the convectors (Burnham Heating Help).
    This falls between two Crown sizes, 446 and 533. At least the 533 will be smaller than the 570 it replaces. I haven't found anything samller that gives 485, closest is a Dunkirk at 479, and I am already not happy with my old Dunkirk.
  • weil mclain eg55

    Weil Mclain boiler #EG 55 is 510 sq ft rating and love them low 3" tappings..
  • 5-section Smith G-8

    rated 525 square feet, would be a better choice than any atmospheric boiler. It is a wet-base unit with a Carlin power gas burner. Unlike a dry-base atmospheric gas boiler, a wet-base surrounds the flame almost completely with water-backed cast-iron. The thermal efficiency (not the same as AFUE) of the wet-base boiler is about 6% better than the typical atmospheric one.

    Here's a pic of a 6-section G-8 we recently installed. If it looks like an oil-fired boiler, yes, it can be had that way too, or changed from one fuel to the other without replacing the entire boiler.

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  • nice installation,Steamhead!

    That's one of the boiler that gonna be a very dry steam with them extra height risers and dropped header system! However, why pressurtrol instead of vaporstat? I've been trying to convict customers to changeover to vaporstat and they can't seemed to justify the costs...
  • tim smith
    tim smith Member Posts: 2,738
    Nice looking job

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