Sizing a Two Pipe Steam Boiler

Bob Gagnon plumbing and heating

I could use some help verifying the Boiler sizing for a two pipe steam system. The connected radiation is 185 sq ft of steam, with lots of unconnected radiators that will never be hooked up again. What concerns me most is the amount and size of steam mains, there is 30' of 3" steam mains, and 110' of 2" steam mains, with other 1" & 3/4" takeoffs. I plan on installing a Utica PEG-E 112 which provides 292 sq ft of steam, using Dan's alternative sizing method I come up with 66,000 btu's well under the 90,000 provided by the PEG 112, do you think this is the correct size boiler for the job?
Thanks in advance, Bob Gagnon

Jamie Hall

@Bob Gagnon plumbing and heating -- the size of the legacy steam mains is not a consideration, provided two things: you provide adequate main venting (you do have to get that air out of there!) and provided you insulate them. If you get that OK, then I, at least, would go with the measured radiation and Dan's alternate sizing. Which suggests to me that the PEG 112 will be too big.

Hopefully one of the pros -- @Steamhead or @Charlie from wmass will comment!

Charlie from wmass

I would use the smaller peg075. That is assuming your piping is well insulated. Truthfully I'd install a Weil Mclain PEG30

Bob Gagnon plumbing and heating

Thanks Jamie for the quick reply, but using both of Dan's sizing methods indicate that the next size smaller boiler will be a little too small, I'm not sure what you mean by legacy mains, all the steam mains are active and supply steam to the second floor.
Thanks, for your help, Bob Gagnon

Charlie from wmass

The smaller boiler already has the pickup Factory built into it's square footage

Charlie from wmass

The GSA 07 5 by Williamson

ChrisJ

Bob,

Here's an easy way to look at it.
You have 44,400 btu/h worth of radiation.

You are looking at installing a boiler with an output of 93,000 btu/h

Do you think that piping will waste 48,600 btu/h worth of heat? More than the installed radiation?

You're creating steam which needs to be condensed back into water at a certain rate, anything slower will build pressure. Some guys like some pressure, but too much is too much.

Go with the PEG075EID. That's even oversized in my opinion if all of the piping is to be decently insulated.

Vent your radiators reasonably slow and vent all of the mains fast. You'll be fine.

My opinion is the theory that you have to heat all of the piping and radiators at once when cold is false. You first heat your boiler, next the header, then it slowly heats all of the mains and run outs, once that's done, it starts filling the radiators, section, by section. By the time any radiator gets steam, all of the piping should already be heated and only losing what it looses through the insulation, nothing more.


I'm currently running a 10% pickup factor. 120,000 btu/h input, 104,000 btu/h output connected to 392 sqft of radiation (94,080btu/h). I'm not suggesting you should do this, just trying to put it into perspective.

Steamhead

The pickup factor is key here. Remember, these pipes are much bigger than needed to supply the now-existing radiation. So there is more metal to be heated.

Dan covers this in Lost Art. With his method you'd take that 44 MBH and add 50% which brings you to 66 MBH. Then select the boiler from the DOE Heating Capacity column.

In the case of the PEG075EID, the DOE output is 62 MBH. So using this boiler would be risky IMHO. Look for something with a higher DOE output.

Charlie from wmass

Steamhead says use the 112 so use that. I use the Weil Mclain/Williamson as it has a bit more water volume for the given fire rate of boiler the 35 and 30 are the same block and have 8.4 gallons of water.

DanHolohan

Yes, I agree with Steamhead. We're trying to get heat everywhere as quickly as possible.

ChrisJ

@The Steam Whisperer
What are your thoughts?

Bob Gagnon plumbing and heating

Thanks everyone for the quick replies, I am going to install the 112, the amount of steam mains in the two pipe system is the deciding factor, full size mains travel up the front, middle and back of the house, and criss-cross back and forth. Three inch and two inch mains all around the basement. I appreciate everyone's help.
Thanks, Bob Gagnon

Charlie from wmass

We can all be experts behind our computer screens but when you are the boots on the ground you have to make the call.

Bob Gagnon plumbing and heating

Thanks for all the help, I should've posted sooner but I've been swamped at work, Steamhead and Dan were correct, the 112 lost a couple of inches of water in the sight glass as it fired up, I think the next size down would've been too small.

Bob Gagnon plumbing and heating

The old vacuum Guage and steam vent worked unbelievably well.
Thanks. Bob Gagnon

DanHolohan

Sweet!

Bob Gagnon plumbing and heating

It was banging like crazy before the replacement, now it's quiet as a mouse, Thanks Dan, for teaching us all, you're the best!

DanHolohan

I learn as much from you, Bob. Thanks.

Bob Gagnon plumbing and heating

My skill level has increases dramatically since I attended your seminars, I never would have attempted a two pipe steam install without the backup this forum provides.
Thanks for all you do...

DanHolohan

And you, my friend.