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Boiler sizing question

Jake2010 Member Posts: 24
I am in the process of looking at replacing an 45 year old American Standard oil Hot water boiler.  It has the original burner and is still working well, I have not had any problems with it in the  9 years that I have lived in the house.  It's original fuel rating was 1.75 gal/hr, I believe it now has a 1.0 nozzle, the boiler itself is rated for I think 150,000btu.  It was originally a tankless hot water system, about seven years ago I had a 40 gal Weil Mclean indirect tank installed. So, I am basically looking into replacing it in the hopes of lowering my oil usage.  I have met with a few contractors and tried to do much research on my own.

A heat loss that was done came in at about 50,000btu.  I have 118ft of baseboard, approx. 2,000sf of living space, 2 zones plus the indirect. It is my wife and I and 3 young children who will be teenagers before I know it. My chimney is 8x13 clay lined.

 I have been looking at the Burnham MPO line and maybe Buderus.  Contractors have mentioned the MPO147, which I think is too big, the Buderus G115/4, and the Buderus G125BE which is an incredible system but it may be too pricey for me. 

That all being said, I have a few questions:

I would like to go with the smallest boiler, would the Burnham MPO 84 or 115 be a good choice? Would the MPO 84 be too small for the Hot water needs, if it is set up on priority?

Would the Buderus G115/3 section be OK?

With either one of these boilers would I be better off using there own control systems such as the Logamatic 2107 or the Burnham IQ control system VS seperte controls for outdoor reset and priority.

Lastly, should I install a chimney liner.

If I am way off base on any of this please feel free to let me know. Thanks for any recommendations you can give me.



  • Ironman
    Ironman Member Posts: 7,350
    Some Answers

    First, Size the boiler to the heat loss; you'll have plenty enough btu's for the indirect. Your baseboard had an output of about 65k btu's when it was brand new, so a heat loss of 50k is probably accurate. And I would lean toward using the manufacturer's controls, especially the Buderus 2107, but there are some good after market controls as well.

    You definitely will need to line the chimney or go with direct vent as the new boilers have much lower flue temps due to their higher efficiencies.

    Here's a recent thread that discusses a similar scenario:

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • furnacefigher15
    furnacefigher15 Member Posts: 514
    Size to the requirement of the DHWH

    I'm not sure if there made for oil, but a 2 stage boiler would work well for you.

    Low stage for heating the house, and high fire if needed during a high hot water demand.

    I personally find the logamatic buderus control too complicated for what it is. I like the tekmar reset controls.

    118 ft of baseboard has a output capacity of about 70,000 btu

    But if the the heat loss is 50,000, then that just mean you have more baseboard then you need.

    I would be comfortable with a with the mpo 84  or a similarly sized boiler.

    75000 btu would be plenty for the dhwh
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