Taking Another Look at Steam Boiler Sizing Methods

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Taking Another Look at Steam Boiler Sizing Methods

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Unhippy

Might want to add this to the Venting Category as its as much about venting correctly as it is about boiler size.

hvacfreak2

That was a fantastic read , thanks Dave.

Erin Holohan Haskell

Thanks, @Unhippy. I've made that change.

Mad Dog_2

Great Read. Dave. Mad Dog

mikeg2015

I feel like I could have written this based on my observations with my Vapor system tell me that I could go smaller, much smaller. Right now I'm fighting a boiler with 1.7 pickup factor, but my header is so big and I have so much cast iron, that my pressures are <1oz until radiators vents start closing, but that takes almost 1 hour firing. Right now it's just "moving too fast" and hard to control. Like MAzda Miata that someone stuffed a V8 into with a throttle that is either on or off. You can make it work if you race to 120 mph that coast back to 30, you'll average around 60.

My system originally had mostly Hoffman #2's I believe as I had 2 left over that were still working.

Jamie Hall

Lovely. I've always liked Dave's work anyway! He doesn't seem to be talking much about two pipe - especially vapour -- systems, but much the same principles can apply. And as an example... consider Cedric. The whole system (1230 square feet total radiation, nice long steam mains). Cedric is sized with a pickup factor of 30%, almost exactly. The whole system is vented through one Hoffman #75 and one Gorton #2 -- and doesn't run over 4 ounces until the radiators are full.

SeymourCates

I found this statement from The Steam Whisperer to be quite interesting:

Maybe it needs to be bigger to meet the heat loss of the house on the coldest day, but why put in a boiler bigger than necessary. Anything bigger will invite shorter firing cycles, especially in warm weather, which greatly hurts efficiency and increases wear and tear on the boiler and system (ie thermal cycling and production of acidic condensate.

We strive to limit the cycling of steam boilers for precisely the reasons he mentions. Once the larger boiler, with the 30% pickup factor, gets into cycling, the efficiency goes in the toilet.

gerry gill

i agree with Dave but would add that as you recalculate the boiler size to the radiator load that 'should' be present if you were installing radiators today, leave yourself a way to take an equalizer tapping off the header and a return tapping in the wet return just in case you have to add a reservoir tank cause at some point you will reach the point where you have enough fire, but not enough water due to todays low water content boilers.