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# Sizing replacement boiler

Posts: 19Member
I am a homeowner, not a pro. Just read this post and got to thinking:

http://www.heatinghelp.com/article/323/Boilers/1551/Taking-Another-Look-at-Steam-Boiler-Sizing-Methods-by-Dave-Boilerpro-Bunnell

I am going to replace my natural gas fired steam boiler.

The projected heat loss of the house after insulation and windows is 27,780.

The current btu output of all the radiators is 36,000.

I have not calculated in any "pick up" percentage.

Currently no insulation on the pipes in the basement but I could add some easily.

What should my target boiler size be?

I am looking at the Burnham Independence models.

Should I go with the IN3 38,000 BTU or IN4 65,000 BTU?

• Posts: 2,668Member
Boiler

Pick a boiler as close to 58,000 input as you can. This should leave you with very few options. The CROWN BSI069 is a nice little boiler, too. You could also install a wet-based gas burner and match the radiation load a lot closer, if not exactly. Underfiring a power burner in a wet-based boiler can yield some very high efficiencies.
• Posts: 19Member
input rating, not ouput?

So i should size based off of input btu rating and not output?

My thought was that I would take the radiator output of 36,000 btuh total and multiply by 1.33 for pickup factor which equals 47,880 and then size based on output rating. But can I undersize the boiler by say 10,000 btu output or should I opt to oversize by 12,000 btu. Do I need to do this pickup calculation or is that already factored in by the manufacturer?

Do these calculations and thinking make sense? Should I even think about the heat loss calculation?
• Posts: 7,356Member
Stop calculating

and just compare square feet (EDR) for both installed radiation and the boiler.  There are potential adjustments for insulation, zoning, etc. but you can start with square feet.
• Posts: 19Member
EDR

Total EDR is 150 sq/ft.
• Posts: 19Member
my main question

This should clear up what I'm trying to figure here. The numbers are VERY close.

I have EDR of approx. 150 sq/ft of radiation from the cast iron radiators.

Under I=B=R specs for Burnham Independence IN3, Steam sq/ft = 158.

Comparing EDR of the radiators and boiler as suggested, these numbers are extremely close to an exact match. Can I go with this boiler or do I have to account for pipes, pipe insulation, etc....
• Posts: 266Member
edited August 2013
Perfect match

If your numbers are correct IN3 is the one you need, It doesn't get better than that, insulate boiler piping and mains, Gorton 2 on the main and hoffman 40 on the radiators, very likely you will only heat the top third of the radiators and that will satisfy the thermostat, very efficient
• Posts: 19Member
excellent

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