Boiler Sizing

Nater2003 · May 27

I'm new to sizing steam boilers. I'm working on bidding a project to replace a oil steam boiler with a propane steam boiler. I can not find the EDR on the old boiler. I did the sq. ft of all the radiators and added for the piping loss. Based on the EDR that I calculated the BTU is 200,000 less than what is currently firing. Any help would be appreciated.

Thanks

Jamie Hall · May 27

If you've added up the square foot EDR of all the radiators, that's the figure you want for the boiler. The boiler rating may say EDR, or may say square feet of steam. That's it. Not more calculation is needed.

Not a bit surprised that the existing boiler is bigger — perhaps much bigger. A common error. Don't do it.

Try to hit the total radiation EDR with the boiler rating — or up to 10 percent smaller. Don't oveersize.

The Steam Whisperer · May 27

What Jamie said and…

if you have a 2 pipe steam system, the proper boiler size required may be even smaller, depending on the system.

bburd · May 27

And… do not add to the square footage of radiation for the piping loss. The boiler square-foot rating includes a 30% piping and pick up factor, which many of us here think is too large for most systems.

Just match the square feet of radiation to the steam square foot rating on the boiler.

Nater2003 · May 28

The old boiler also has two domestic coils. Any input on sizing BTU to domestic coils?

Jamie Hall · May 28

Domestic hot water? No increase needed. I suppose in rare circumstances — such as, perhaps, a commercial laundry (not a laundromat!) you might want to check the actual increased BTU demand. But in general, no increase needed.

EdTheHeaterMan · May 28

As mentioned by @Jamie Hall, @The Steam Whisperer, and @bburd. Do not try to get smart with converting square feet of steam or EDR to BTUs. It is a fools errand and will have lots of room for error. BTU Input, BTU Capacity, BTU Gross Output and Net BTU ratings are all different for each boiler. Understanding which one to use is confusing so don't even try.

Take the EDR from your radiator count and select the boiler based on Sq Ft Steam rating of the replacement boiler.

KC_Jones · May 28

https://forum.heatinghelp.com/discussion/201480/boiler-sizing

The person before you did their job very wrong, don't second guess yourself based on that.

Size to the system EDR. What boiler is currently there is 100% irrelevant.

Boiler Sizing

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