When Is A Boiler Too Large?? - HVAC - DIY Chatroom Home Improvement Forum

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Old 07-18-2013, 11:55 AM   #1
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when is a boiler too large??

I bought a used Weil McLain Ultra 155, that is 2yrs old. The previous owner removed it to go forced air (want central air). Excellent price,but I had no time to research.

I called the heating and plumbing specialist to install the boiler. He says, while I require a boiler that's 100,000 btu, the 155 (123,000 btu) is too large to replace my existing boiler (which is a Weil McLain boiler from the early 1960's when the house was built). He suggested it was not worth installing...but he had a Weil McLain Ultra 105 (81,000 btu), which is currently in stock for $4,000 plus installation). not sure about that.

My question....... is the 155 boiler too large for my application? Should I bother having it installed? Will it cost me that much more to run than a ultra 105?

I live near Buffalo, NY



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Old 07-18-2013, 04:49 PM   #2
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Ultra 105 min input is 21,000 BTUs.
Ultra 155 min input is 31,000 BTUs.

No problem using the 155 in your house. It is bigger then what you need. But will work fine, as long as its piped up properly.

You probably only need an 80.


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Old 07-19-2013, 01:40 AM   #3
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First off do a Manual J heat loss calculation for your home. Many centuries ago it used to be that HVAC companies stood out on the curb and sized the boiler from outside the home... I think there were candles, incantations and chants involved. Now days us modern techs use what is called a heat loss in order to size a boiler properly to the requirements of the home. So that would be one way to tell exactly what your home would need as far as boiler size.

As far as putting something that is a little oversized for your home, it won't hurt anything... maybe shorter run cycles and perhaps more frequent and as a result a tad less efficiency all around.

Start with the heat loss. Get that figured out, if you cannot figure it out there are a few sites on the web that will give you software to help do the calculation. After that you will have a clear picture of how oversized the boiler may be... if it is.
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Old 07-19-2013, 06:35 AM   #4
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When hooking this unit up make sure you follow the manufacturers instalation procedure to the letter. The primary (boiler) loop is critical in ensuring these boilers live. I have seen several where the installer hooked them up in a conventional manner and cracked the heat exchangers
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