Oversized Boiler, Is It Costing Me Money, How Much?

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Posted by Joe Howell on October 29, 2001 at 07:58:39:

Good Boiler Folks,

I have the following boiler hooked up to a two pipe system.

Bryant (Looks to be between 1960-1970)
Rated 880 ft^2 EDR
264 MBtu/hr Gross

I calculated the existing square feet of my radiation in my house using the Colonial website and I came up with 484 ft^2 EDR. If I assume I need a 1.50 Pickup factor that would mean a 174 MBtu/hr gross requirement. For the replacement boiler I am thinking of purchasing, the efficiency is around 80%, so the input required is 210 MBtu/hr (from their literature).

If the efficiency of my current boiler is assummed to be 60%, the input would be approximately 440 MBtu/hr. This is over double the input I need. Does this sound reasonable.

The problem I am having is that the boiler will come on and within 10 supply steam to the radiators. However, it will reach the high pressure on the Pressuretrol (1-1/2 psig) and cut the fire, then the pressure will decrease and start the fire (.5 psig), and continue on like this for about 45 minute before satisfying the thermostat. Once everything is hot the boiler will fire for approx 2 minutes until it reaches 1-1/2 psig, then off for about 1 minute until it reaches 1/2 psig and continue on like this.

Should the boiler input (gas burner and valve) be sized to supply the amount of energy needed (in my case only 210 is needed)and no more or should it be oversized? Are these components automatically sized for the input when one buys a boiler?

All other things being the same (piping, etc). Is this way oversized boiler costing me on my gas bill. I am thinking that I can save a lot on gas costs if I install the proper sized boiler since the input will be way less and the efficiency will be approx 20% better. Is this correct?

How can I fiqure out what my input is currently if its not written on the boiler?

Any help is appreciated.

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