New Boiler & EDR Calculations

OldSteamy

Hello. At this time I am planning to replace my old, oil-fired steam boiler with a new gas-fired steam boiler from U.S. Boiler Company. My home was built in the 1930s to '40s and has (8) Burnham tube-type radiators and (1) column-type Fero. The current boiler is oversized so using the sq ft rating from the old unit is not possible. Looking towards getting the correct size boiler, there is a need to calculate the EDR for the home. The Burnham tube radiators range from 4 tubes to 5 tubes and are 19"to 26" in height. Of these, (7) of them have 1-1/2" section spacing and a newer, replacement radiator has 1-3/4". The FERO is a 3-column type that is 31" in height with 2-1/2" section spacing.

Going through the numbers, I am getting around 280 sq. ft. for EDR (rounded-up). The contractor who quoted the installation of the new boiler got around 380 sq. ft. for the EDR. Based on the numbers, I believe the U.S. Boiler Company SteamMax 125 is the right choice and the contractor is insistent on the SteamMax 150. 🤔 The header, mains and risers (where visible) are covered with 1/2 thick fiberglass pipe insulation so I feel the NET values are OK to use with the 1.33 pick-up and a 1.5 value is not needed.

Having lived with an oversized boiler for too long (only now have the $$ for a replacement), I want to make sure that I am not going to live through the same short cycling of a new boiler producing steam faster than the system can handle and turning on and off every 2 to 5 minutes. 😞

Here are the radiator types and sizes that are in my home. I would like to ask if someone can confirm the best charts to use and what would be the best EDR value to use. Bear in mind that the end result I am looking for is to have the right sized boiler based on the EDR needed, not whether or not one calculation is right and another is wrong. 🙂

Rad	Manuf	#-Type	Section Spcng	Height (Flr-Top)	Num of Sections
1	Burnham	4-Tube	1-1/2"	25"	14
2	Burnham	4-Tube	1-1/2"	25"	24
3	Burnham	5-Tube	1-1/2"	20"	10
4	Burnham	5-Tube	1-1/2"	20"	14
5	Burnham	5-Tube	1-1/2"	20"	20
6	Burnham	5-Tube	1-1/2"	26"	12
7	Burnham	5-Tube	1-1/2"	26"	24
8	Burnham	4-Tube	1-3/4"	19"	12
9	FERO	3-Column	2-1/2"	32"	8

Steamhead

I'm getting 295.3 square feet from your chart, so the 125 should be fine. But- are your steam pipes insulated, and do you have proper main vents?

OldSteamy

The header, mains and risers, where visible, are insulated. The mains are well vented by Gorton Air Eliminators following a calculation of the air within the main piping and sizing at 1oz of steam pressure.

Steamhead

https://forum.heatinghelp.com/discussion/comment/1897229#Comment_1897229

Great- had to ask.

EdTheHeaterMan

I used the Burnham boiler sizing guide and got 411.

But that book does not have the thin tube listings. I use to use the Weil McLain sizing guide and that listed both the standard tube and the thin tube with dimensions of the sections. Do your 4 tube width sections measure 7" and 5 tube width measure 8-3/4" Like the attached chart? If they are smaller then you may have thin tube and this calculation is not for you.

OldSteamy

Thank you EdTheHeaterMan for your comments and detail.

I believe that the radiators in my home are the much older, slenderized Burnham radiators. The widths are as follows:

Burnham 4-Tube, 1-1/2" spacing, are about 4-7/16" wide

Burnham 5-Tube, 1-1/2" spacing, are about 5-5/8" wide

Burnham 4-Tube, 1-3/4" spacing is 4-7/16" (new, replacement slenderized)

Fero 3-Column / Tube, 2-1/2" spacing is about 5-1/4" wide

The Burnham Heating Helper is a great resource, but the sizing of the radiators in this reference do not match the sizing of those in my home. I believe that the contractor used the Heating Helper for his original calculation.

EdTheHeaterMan

With that additional information and some other steam rating tables to match your dimensions. I was able to get a more accurate EDR of 318. So the Burnham Steam max 125 is spot on!