Choosing New Gas/Steam Boiler?

Old 02-09-09, 09:27 AM
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Question Choosing New Gas/Steam Boiler?

Our present gas/steam 175,000 BTU boiler needs to be replaced:

1. I have 3 estimates and 4 different high efficiency boiler recommendations, Weil-McLain, Utica, Crown and/or Peerless. Which do you recommend and why?

2. For our present size house, we could go down one size to 140,000-150,000 BTU, but that would not allow us to ever increase the size of the house if we could afford to build on.

Are we better to put in the 175 BTU or will this be too large if not now needed and therefore less efficient?

Thank you for your help!
Old 02-09-09, 01:14 PM
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First things first.

Do you have a steam system or a hot water system?

Boilers for steam systems are sized according to the output of the radiators. This is known as the "connected load" and is given as EDR (equivalent direct radiation) in units of square feet. For example, 450 sf EDR.

Boilers for hot water systems are sized according to the heat loss of the building.

The fact that you state the estimates are giving options for "high efficiency" boilers suggests you have a hot water, not steam, system. There aren't really "high efficiency" boilers for steam. Yet.

So assuming you have a hot water system, it would appear that probably none of the estimates you have are based on a building heat loss. I'm guessing this based on the fact that a 140,000-150,000 BTU/hr boiler could, all by itself, heat four or five of the ~2000 square foot houses in my neighborhood. So unless you have an 8000-10,000 square foot house, the proposed boilers are too big.

Point being that you should do or have done a proper heat loss calculation. It only takes a couple hours and will save you a lifetime of energy costs. Free software is available here:

How to get Hydronic Explorer 2

And you should read this thread, which is a sticky at the top of this forum:

It will help you figure out how to proceed. Check back here with heat loss numbers. Lots of folks to help understand the numbers and make suggestions for boiler size, control features to improve comfort, ways to build in some "cushion" for a future addition to the house, etc. etc.

All that said, if you really do have a steam system, then the 175k BTU input figure may be derived from the original measuring of the EDR and using a manufacturer spec for the old boiler that translates EDR to BTU/hr. In order for your current estimates to be in the ballgame, the contractors would have had to measure each of your radiators, determine the total EDR, and relate the square feet of steam to BTU input. It would be possible to have a slightly larger steam boiler than needed, and yes, sizing it down would mean it could be difficult to add more steam radiators down the road.
Old 02-09-09, 02:20 PM
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Steam as stated previously is always sized off the existing radiators. Did the contractor measure all your radiation? Are the main pipes in the basement insulated?
See this link for more info on steam boilers.
Steam FAQ

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