Help Sizing Steam Boiler w/ Uninsulated, Exposed Piping

Ultrasaurus

Hey all,

Another Burnham Independence bit the dust. Photos at the bottom, you may like to see it!

I've read through many posts and Dan's articles here. I'd like to get a sanity check on sizing a replacement WM boiler since my house has uninsulated piping, which complicates the sizing. Two contractors have suggested a larger boiler size than I have calculated.

• 1-story attached house with basement in NYC.
• 42'x22' footprint
• 1 Pipe System
• Portions of pipe are exposed & uninsulated and provides heat to the occupied basement
• I assume the rest of the piping hidden behind walls/basement ceiling is also uninsulated

First is radiator EDR counts:

Room / location	Type	Height (in)	Depth (in)	Tubes / columns	Sections	EDR
Front Room	Tubular	20	8	5	13	34.7
Front Door	Tubular	23	6	4	6	15.0
Living Room	Tubular	20	Unknown	5	16	42.7
Bathroom	Tubular	26	5	3	5	11.7
Small Bedroom	Tubular	20	8	5	10	26.7
Big Bedroom	Tubular	20	8	5	11	29.4

..for a grand total of 160 EDR on the radiators.

Piping: I have about 40 feet of exposed 2.5" pipe (9" circumference) which is directly radiating heat into the basement rooms. This is coming directly out the top of the Burnham.

From the radiator layout, I estimate there's about 40 more feet of pipe that is hidden in the basement ceiling/top floor, and I assume uninsulated.

I have only considered the exposed portions (9 inches * 40 feet = 30 sq ft of pipe surface area) and I assume this directly translates to 30 EDR.

..so 160 EDR + 30 EDR = 190 EDR.

Allowances: Now Dan suggests we can use a 1.5 factor instead of 1.33 factor for dead-end/uninsulated piping and should be compared to the DOE rating.

…so 190 EDR * 1.5 factor * 240 BTU/hr per EDR = 68400 BTU/hr, or ~69 MBH.

Selecting the size: Here's an excerpt of WM's sizing chart:

Model	DOE HEATING CAPACITY (MBH) STEAM
EG-30-*	62
EG-35-*	82
EG-40-*	103

I suspect the EG-30 would be sufficient, but I have selected the EG-35 as a very conservative measure for my anxiety. However, I had two contractors stop by to provide quotes, and their sizing has me doubting myself.

• 1st suggested the Crown equivalent of an EG-55 because I had "6 rooms"
• 2nd one suggested I size up to EG-40; he doesn't feel comfortable installing the EG-35. He cited experience, but was unable to produce numbers to justify it.

I've reached out to to a few contractors listed on this forum too, and I'm pending their response at the moment (it is the busy season), but I'd just like a better idea where I stand in terms of sizing from the good people here. Happy to provide more info or photos. Any checks on my calcs, thoughts on the uninsulated piping's contribution, and suggested boiler sizing is very much appreciated.

One note is that we're happy with the heat with the existing Burnham (rated 87 MBH) even with the massive leak. The basement is a bit chillier, but I assume this is not a boiler sizing issue but rather the lack of basement radiators.

As promised, some photos of the Burnham and why we need replacement:

And here are some photos of our radiators:

Front room; the other radiators have the same chamfered style:

Front door has a different, rounded style radiator:

mattmia2

eg30. even that is too big.

EdTheHeaterMan

1. Can you tell us how ofter the boiler reaches the high limit pressure and what that pressure is?
2. Can you tell us how long the thermostat calls for heat?
3. Can you tell us how long the burner stays off after it reaches the High limit pressure?
4. Can you tell us how long the burner operates for after the pressure drops below the cut in point?

If your system is oversized for the connected radiation (including the piping), it will short-cycle—for example, 4 minutes on, 3 minutes off, then 4 minutes on and 3 minutes off again and again. If this continues for 30 minutes or longer, the boiler is too large, and you can feel comfortable with your calculation and use the EG-30 or EG-35.

On the other hand, if your boiler does not cycle on pressure, it is probably sized correctly, and you need a boiler with a DOE output of approximately 87,000 BTU/h.

When a contractor says They are not comfortable with something, then tell them that their comflrt is not your concern. My own comfort is what I'm interested in. And I'm the one paying for this level of comfort. The math shows that a EG 30 is more than enough and it you can't install it properly, then perhaps I need to get another company.

Now do your homework and select the proper size boiler based on industry standards and not some gut feeling and X number of years experience. Can you give me a number of a satisfied customer so I can ask then if their boiler short cycles because you selected something for your comfort and not their comfort? And it must be a STEAM boiler not a hot water boiler system.

Jamie Hall

The 1.33 factor is built in — precisely to compensate for uninsulated piping — so you don't have to do the math (there are other minor reasons for it, too).

Forget converting to BTUh.

You will be much happier — and simplify your life considerably — if you size your boiler based on the EDR of the radiators it is intended to power. The EG-30 is rated ate 196 square feet; you have 160 square feet. The -30 should be quite adequate, and anything bigger will short-cycle.

ethicalpaul

The EG-30 will short cycle too, but they can minimize it by not setting back their thermostat at night of course

KC_Jones

You want the smallest boiler made. Period.

Ultrasaurus

Thanks all for the quick replies, and glad to know I'm in the right ballpark.

My remaining concern is accounting for the uninsulated piping, without double-counting anything.

• Dan’s article says "they base this one-third "pick-up" factor on insulated mains because steam mains are supposed to be insulated."
  https://heatinghelp.com/systems-help-center/why-you-should-insulate-steam-pipes/
• Likewise, WM's manual states "Steam ratings on an allowance of 1.333. An additional allowance should be made for unusual piping and pick-up loads."

The occupied basement has no radiators, and I intend to keep the approximately 40 feet of exposed 2.5" pipe bare for basement heat. I also estimate another 40 feet of concealed piping, but its insulation is unknown.

Dan's example works out to 265 BTU/h per foot; or 10,600 BTU/h for 40' length of pipe.

I ran the numbers with a few different assumptions, the first two of which probably double-counts some allowances:

• Adding 10600 BTU/h for exposed 40' section; and using higher pickup 1.5 for the remaining pipe:
  • 160 EDR * 1.5 * 240 BTU/h/EDR + 10600 BTU/h = 68,200 BTU/h → Size for EG-35
• Adding 2*10600 BTU/hr for all pipes in the house (80'), assuming all uninsulated, and going back down to a 1.33 pickup factor.
  • 160 EDR * 1.33 * 240 BTU/h/EDR + 21200 BTU/h = 78,800 BTU/h → Size for EG-35
• Use a blanket 1.5 factor to account for uninsulated pipe:
  • 160 EDR * 1.5 * 240 BTU/h/EDR = 57,600 BTU/hr→ Size for EG-30

I’m open to the EG-30; I’d just like to understand how to verify my radiation capacity with the exposed pipe remaining uninsulated.

Ed- regarding your questions, I regret I don't recall these attributes for the existing boiler, as it was not fired up since last winter, and I have not paid as much attention to its function as I should have until now. I assume that with the waterline leak, the pressure is not a good indicator of function anyway. I'll keep looking for a contractor that can show me their numbers on my heating system and perhaps a number of their satisfied customer as well.

EBEBRATT-Ed

Your radiation is 160 EDR. The EG 30 does 196 EDR

the 196 edr on the EG-30 includes a 1.33 PU factor already built in to cover your uninsulated pipe. Even the EG-30 is larger than you need. Don't let ANYONE talk you into a larger boiler

mattmia2

2.5" pipe has an edr of about .75 per foot. your 40 ft of pipe has an edr of about 30 ft^2. if you want to calculate the edr of your pipe, you should add nothing else for the pickup and use the actual output of the boiler, not the square foot rating with the included pickup factor. you can see that is around 20%.