Replacing hot water radiator boiler- many questions

Old 10-30-06, 07:26 AM
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Replacing hot water radiator boiler- many questions

I need to replace an ancient American Standard A-5 cast iron boiler (oil)which has been in use for 30+ years (and was used when installed) and has finally sprung some unrepairable leaks.

I believe the system has 3 zones, one of which(the smallest and about 500 sq. ft.) is already hot water baseboard.
The other 2 zones are cast iron radiators. So about 1,800 sq. ft. is being heated by radiators.

The total square footage of area needing to be heated is 2,300 sq. ft., and it is all on one level. 8' ceilings throughout.
This building is a large old gambrel roof barn which has been renovated, and only the lower level is heated. I would say that for heat loss it would qualify as being in the category of an older home with moderate insulation.

I believe that the old boiler, which was 550,000 BTU and held about 120 gallons of water, was a bit of overkill in the first place. It certainly has not been an efficient system in regard to fuel consumption for a long time.

My questions concern the following:
1) many people like the radiator heat, so keeping the existing radiator system is a consideration. What size boiler (roughly) would be needed to handle this amount of square footage? Any recommendations as to brand of boilers to consider? Any rough estimates as to the cost of a new boiler that would handle this area?

2) The other option is to replace the radiators with baseboard units. Any recommendations as to the size and cost of a new boiler for a baseboard heating system to handle this size area?
Also any recommendations as to the brands of boiler to consider? What would be a rough estimate for the cost of new baseboard units for heating the approx. 1,800 sq. ft. now heated by radiators?

Another question, because cost of the system replacement is a big consideration: Does it make sense (given the high cost of copper at this time) to switch the system from radiators to baseboard?
I'm thinking about the initial expense of a new boiler that would handle the existing radiator system compared to a boiler that would handle all baseboard, and also the cost of replacing the existing radiators with baseboard units.

My own feeling is that it would be best, in terms of efficency and future fuel savings, to switch over to all baseboard at this time, since we need to replace the boiler. It seems that the additional expense of the baseboard units would be offset in the long run by having a more efficient system.

This building is owned and used by an organization that I'm a member of, and we will be contacting local professionals for estimates to do the work. I'm on a commitee set up to address the replacement, and asking these questions just to get some initial ideas. Do you think it would be wise to actually have a heating engineer come in and lay out a system for us, or can we simply go with a local plumbing/heating contractor to lay out the system for us? I'm in the building trades myself, and I tend to think that a qualified contractor can tell us what we need, but some folks think we need to consult with a heating system engineer.

Thanks for any and all advice.

Last edited by GrandpaBill; 10-30-06 at 08:29 AM.
Old 10-30-06, 04:33 PM
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As one Grandpa to another:
First you need to determine the heat loss of the building. There is a program you can download for this purpose from

The next thing is to determine the heating capacity of the existing radiators. Dan Holohan has a book called EDR (Every Darn Radiator) which gives ratings for a lot of different radiator.
You might be able to find it elsewhere but I know you can get it at the above link.

As to costs: It is highly unlikely replacing the radiators with baseboard would be cost efficient.

Equipment selection is often a matter of personal preference.
Old 10-30-06, 05:09 PM
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Thanks Grady.
I actually found the link to the slantfin software in another thread where you had posted it, and I downloaded it this morning. I'm in the process of punching in the info.

Interesting to know that replacing the radiators with baseboard would not be cost efficient. They're still in good shape, and they do heat the place just fine.

We have lined up a couple of local plumbing/heating contractors to look at the system and advise us on the boiler requirements.
Old 10-30-06, 05:25 PM
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Get 3 bids from companys that have been around you for a longtime. Thats the best way to go . They should run a heat lose and give it to you with the bid .
might also go to There you can compare fuel cost.

With that 550K you have now could you get #5 oil and gun for it there????

Old 10-30-06, 07:13 PM
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Ditto on what Grady and Ed have said. Definitely keep the radiators. Replacing with baseboard is going backwards on the desirability scale, the money scale, and whatever other scale you can think of.

It is likely that the radiator zones will need a different water temperature (cooler) than the baseboard, but that's no big deal. There are piping and control strategies for that.

For 2300 sf, you likely do not need a heating engineer, especially if you already have adequate heat. You need a decent heat loss calculation and a contractor who knows how to deal with multi-temperature systems.

Post back here with the slantfin results.

Unless you are in a 2300 sf cardboard box in the arctic, it's unlikely that you need a 550k BTU boiler. Probably more like 120k BTU if "older home with moderate insulation" is reflected in the heat loss. The EDR radiator calculation will be important, however.

Also, if you've got a group to do some handywork, consider spending a day doing basic sealing (caulk windows, put expanding foam in infiltration points in the attic and basement) and maybe add some insulation where you have access. These kinds of things are fuel you buy only once....
Old 11-01-06, 04:18 AM
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Thanks for the replies, everyone.
I'm still figuring out the slantfin software, but will post my results if I'm succesful in using it. Reading through the "help" manual now.

We have two highly recommended 'old time' professionals looking at it this week and giving us estimates. We'll get a couple more estimates as well.

I agree that 550,000 is overkill for the space that we need to heat, so we'll see what size boiler is recommended.

We're definitely keeping the radiators and doing a few insulation and weather stripping projects on our own.

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