Boiler Sizing Quandary

HeronHouse

Splitting off from my earlier thread: We are converting to gas from oil and replacing our ancient boiler and DHW. Our plumber is sure we'll be fine with a certain model of boiler, but if I go strictly by my calculations based on Lost Art of Steam Heating, it is a bit undersized.

I came up with 286 EDR for our current radiators. Since we might swap out a few radiators in the future, I could see us winding up as low as 266 EDR or as high as 292 EDR.

The plumber is going with New Yorker boilers because he knows them and we are getting a good deal on them. The CGS40C is rated for 263 EDR and the CGS50C is rated 354 EDR.

So, depending on how we swap radiators, we would be between 1%-11% undersized with the smaller boiler. Or we'd be 21%-33% oversized with the other.

But as Jamie Hall pointed out, there's a 33% pickup factor in there, and maybe we don't need it all? We don't any crazy piping, and although they took the asbestos out I intend to go back and insulate extremely well. It's a 3.5 story row house but the footprint is quite small (18'x45') and there are only 10 radiators total. And he will be putting in brand new main vents (where there were none!).

We like and trust our plumber, generally. He's not crunching numbers, but he's going by 40 years of experience, intuition and "this model has worked great in places bigger than yours", and that's pretty hard to argue with. But I'd very much appreciate some 2nd opinions!

Thank you thank you in advance.
H

Ironman

Well, that line “that this boiler has worked in larger places than yours” is pure bunk. A steam boiler MUST be sized to match the connected radiation, not the size of the house. It’s kinda like an air conditioning system: you don’t hook a 3 ton outdoor unit to a 5 ton indoor unit. The steam system has to be able to emit as much heat as the boiler produces for the process to work properly. If you wish to down size the boiler to match the actual heat loss of the house, then the radiation would have to be down sized accordingly.

That being said, I’d recommend going with the smaller boiler. If you’re within 10%, you should be fine. A pickup factor of 33% has a good margin of error and is usually high.

Make sure your plumber pipes it according to the I/O manual. That’s the MINIMUM standard. A drop header is preferred and only requires 2 more nipples and Ells. Use both steam taps, not just one. Flush or replace any wet returns that are clogged or leaking.

JUGHNE

You are lucky that you don't have a plumber with the "bigger is better" attitude.

I agree with all that Ironman said above.
Especially the new near boiler piping.

Do you know the rating of the old boiler?

FWIW, just for reference to sizing, I service a 1953 church that has 2689 (from blueprints) connected EDR of 2 pipe steam convectors.
It is fed by 2 boilers with 633 EDR nameplate ratings.
I was astounded that the 1266 would heat the 2689 EDR.

However pipes are newly insulated, in a piping tunnel.
They do not use any set back control.
It heats the building fairly well and will even cycle off on temp, never pressure.

JUGHNE

How will you heat DHW?

EBEBRATT-Ed

I agree with @JUGHNE & @Ironman . The smaller boiler is fine as long as he pipes it correctly

HeronHouse

JUGHNE said:

How will you heat DHW?

We are going with an indirect.

AMservices

If you convert your radiators EDR (286) to BTU,
286 X 240 = 68,640 BTU
to get the 33% pick up factor,
68,640 X 1.33 = 91,291 BTU.
You want a boiler with a D.O.E. heating output around 90K.

To find boilers hidden pick up factor ÷ heating output by 240

New England SteamWorks

Weil McLain EG-35. All day.

Not a big fan of New Yorker. There's a reason it's the price leader.

Dave0176

New Yorker (rebadged Burnham) in green and as @New England SteamWorks said EG-35 or go with a rebadged Weil-McLain in the Williamson GSA 100,000 for a slight savings.

John Mills_5

Not to hijack the thread but the answer to my question may be beneficial to the OP as well.

I've asked before, but what is the drawback to the New Yorker? We've been using them for hot water installations just because of the low price with 0 failures. Why wouldn't we want to sell them and the OP not want to buy them?

HeronHouse

Thanks for the info & thoughts, all.

@Ironman @JUGHNE @EBEBRATT-Ed thanks for the feedback. Going with the recommendation for the smaller one, and we will make sure everything is piped and insulated right.

I posted a month ago asking if anyone had any boiler recommendations or warnings -- @New England SteamWorks where were you then? haha

Anyway my guy has installed quite a few New Yorkers, has for a long time, and says he hasn't had problems with them. And now it's been bought! So fingers crossed.

You all have been invaluable. I'll check back in and let you know how it goes.