Boiler Replacement

We are looking into replacing our old 120,000 BTU gas boiler with a new one. Our house is a typical single family, late 1800’s row house- 3 floors with a cellar, front and rear exposure, approx 2000 sq ft with 6 large cast iron radiators. I went to a number of websites/blogs and most of them said, that a large number of people have boilers that are too big for their houses: “do a heat loss calculation”. We did the calculation and we came up with 95,000 BTU’s, plus another website asked for some basic info and that heat loss number was 99,000\. Our plumber is suggesting either a Utica MGB Series 125,000 BTU or a Weil Mclain CGA-5 140,000 BTU. Because of the results we suggested the Weil Mclain CGA-4 105,000 BTU, but he insisted it would not be strong enough, since we need to take into consideration all the water that needs to be heated for the old cast iron radiators. Which one should we go for? I would greatly appreciate any thoughts or insight on this subject. Thank you very much.

reno101

in Plumbers and Plumbing 11 years and 5 months ago

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biggles | 11 years and 5 months ago

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both types are cold starts 140K will do fine might consider changing some of those rads to baseboard runs…

steam_man | 11 years and 5 months ago

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Well, the OP says his/her plumber suggested the Utica. You never know why.

eman134 | 11 years and 5 months ago

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steam man… since they are considering a utica as one of their choices, I doubt if an HE system is within budget

steam_man | 11 years and 5 months ago

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reno101, considering it is a hot water system, I would look into one of the high efficiency condensing boilers. Maybe a Triangle Tube or perhaps Viessmann. Don’t forget an indirect water heater!

Master Plvmber | 11 years and 5 months ago

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That’s it, reno101\. You understand.

reno101 | 11 years and 5 months ago

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Master Plumber: So if I understood you correctly, my heat loss calculation needs to be closer to the “Net Ratings” (which is 102,000 BTU on the Weil Mclain CGA-5) not the 140,000 BTU “Input Rating”. Which means the CGA-5 would not be over sized for our house…..is that correct?

brucef | 11 years and 5 months ago

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Heat loss for row houses is a mature process. The common wisdom that the old boilers are specced way too large was true when oil was 25 cents/gallon, and insulation was barely an after thought. Often old boilers are too large if you have sealed up air infiltration and insulated. What your vendor said regarding “old cast iron radiators” is factually incorrect. You are burning fuel, the percentage of which is used, or wasted up the flue, then send that heat to radiators. Cast iron is expensive but an excellent medium. It requires neither more nor less energy, because by definition we want it to escape into our homes, heating our air. You are considering an investment that requires more than web research. Get a real heat loss by someone who knows what they are doing, and you will save in the long run.

ellenlourie | 11 years and 5 months ago

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Why would not you install high efficiency system? Have qualified boiler installer do professional heat loss calculations. The boiler size you come up with probably at least 30% higher than you need.

Master Plvmber | 11 years and 5 months ago

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First of all, I hope you have a hot water system and not steam. What your plumber should explain to you is that your heat loss calculations are giving you a total BTU *output* required from a boiler. The boiler ratings you’re quoting are *input* ratings based on a roughly 84% efficiency. That means you’ve got to meet your calculations with the “DOE Heating Capacity” values which take the ~16% combustion loss into account, or the “Net Ratings” which take additional pipe and building envelope losses into account, too.