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What size boilers

JOE_99 Member Posts: 15
Have 2 family in NYC,wood frame,3-1/2 insul in ceiling and side walls,2 story,about 30 yrs old (taking out hot air). Have used 2 heat loss cal's and come up with 17,000 (tenant),38,000 for rest of house(part of 1 st floor and all of 2nd fl).Want gas,have chimney,cast iron,BB hot water heat.I need two separate boilers,conventional.What size would be the best for each heat loss.Where can I get a small one for the 17,000 btu.


  • Tom Hopkins
    Tom Hopkins Member Posts: 552
    Good for you!

    You are among the elite of owners. Most have no clue about the essential need for a bona-fide heat loss evaluation, BEFORE sizing a boiler!

    A mod-con (modulating AND ondensing, high efficiency) boiler is a great idea. A few manufacturers make boilers that at maximum output, do 50,000 BTU's. Those that modulate, will drop the firing rate down to ~ 17,000 BTU's and sit there all day long; never cycling (the ultimate in efficient operation).

    Unfortunately, the heat loads are always stated on the coldest days of the winter, something that only happens a few days a year. The entire remainder of the year, any boiler will be well oversized!

    Think about integrating an indirect hot water maker. Mod-con boiler all get in the 90% and up efficiency AFUE ratings. Why install a 40-gallon "plain jane" water heater you'll use 365-days a year, when you can easily use the boiler to provide 90+ year round efficiency?

    Make sense?

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  • kal_2
    kal_2 Member Posts: 60
    you need a modcon

    Like a Lochinvar knight 80 modulating condensing boiler together with a 40gal indirect domestic hot water tank

    - you can use a knight 150 with a larger indirect for the bigger apt

    or put the whole house on a 210 with an 80 gal indirect

    Those boilers will be almost dead on when modulated down your steady state heatloss calculated loads on a design day
  • ALH_4
    ALH_4 Member Posts: 1,790
    Heat Source

    Here is another case where I would use the Bradford White Combi2 water heater with internal heat exchanger coil for the 17,000 btu/h tenant.

    For the rest, the best you can do is to buy an 80MBH mod/con boiler, or a small cast iron boiler. I would lean more toward the mod/con for the sake of efficiency. There are a few models available in the 20-80MBH modulation range. Either the Viessmann Vitodens 200 6-24 or Vitodens 100 8-30 would work great.

    Thermostatic radiator valves and constant circulation would make a nice addition to your cast iron radiation.

    I don't think I would use a boiler larger than 110MBH, even for both units.

    EDIT: In response to Ken, I have no affiliation with any boiler manufacturer. I mention the Viessmann boilers as an option because I have experience with them, and I feel it is helpful to have a starting point to begin your search. I see no reason to be so politically correct as to not mention brand names. There are many other boilers that would work very well.
  • Tom Hopkins
    Tom Hopkins Member Posts: 552
    I didn't mention a boiler brand...

    Because you didn't ask that; but neither of the ones the two next posters suggest - would be on my "short list" of boilers to use.

    Sometimes you need to consider the basis of a suggested unit. If the brand is just one of many a contractor likes, that's one thing. But if it's a manufacurer or wholesaler, their suggestions are not based on "information" but rather self-promotion and marketing.

    I have no knowledge of what group these posters belong to (independent installing contractors - or - manufacturer/distribution chain marketing people) But there are many manufacturers out there; most of whom are superior to the B/W or Lochinvar, and - at around the same cost or less...

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