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Hydronic air handler or Modulating furnace

jp_2 Member Posts: 1,935
possibly the furnace. everytime you change mediums you lose efficiency. heat water to heat air opposed to heating air somewhat directly, both systems heat a heat exchanger first.

but i agree with brad too.


    J. WALTER BOOTH Member Posts: 21
    hydronic air handler

    What would be the most efficient?
    a new modulation furnace both flame and cfm, or
    a hydronic air handler supplied by a Pinnacle boiler
    with outdoor reset.
    currently I have two furnaces one for the first floor, one for the second, the heat loss is just over 130,000btu,
    which is why i was considering the air handler but can not
    find any info on how efficient the system will be if the boiler modulates but the blower does not.
  • Brad White
    Brad White Member Posts: 2,398
    Things to think about...

    Good question and I really do not have an answer but this is the methodology I would use to help sort it out:

    1) One point of combustion versus two: the compounding of inefficiencies. Can you run the Pinnacle down less than the modulating range of any one furnace?

    2) Will the two zones run together much of the time? In other words can they both enjoy a turn-down within the modulating range of the boiler? Say both are running intermittently on a 30 degree day and the boiler is modulating near 30 percent, allowing more constant burns?

    3) Cost of electricity to run the fans: Hours at what kW draw?

    3A) Who says you cannot modulate a Hydro Air AHU and have the best of both?

    I guess it depends on the real-time efficiency of the furnaces (and two points of maintenance but also some redundancy should one fail) compared to a hydro air system where you can vary the distribution side a bit.

    Not a full answer by any means, just some random drive-by thinking.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    Unless there has been a recent new introduction, the Rheem Presitige series furnace is the only one I know of that combines a nearly (something like 60? steps) modulating burner with a variable-speed (far fewer steps) blower and most importantly an integrated thermostatic controller. By combining variable burner output with variable delivery of heat and a controller that understands how to make these things work together, it is essentially the Vitodens of forced air furnaces...

    While the Rheem is fairly new I find no web evidence of it being a disaster like the Lennox "Complete Heat". Providing it's available in the appropriate sizes and budget allows, I'd choose that over hydro-air.


    While Brad is quite right that there's no reason a mod-con (using reset) cannot drive multiple air handlers there are some serious complications. Unless the air handlers are variable speed (and regardless of how generously their heat exchangers are sized) you won't be able to have much slope in the reset curve unless the air handlers are also variable speed.

    Unless I've missed something there are no thermostatic controllers that understand how to make a mod-con "talk" to a variable speed air handler and vice-versa. Such is a true requirement if the highest comfort and efficiency are your goals.

    With any variable speed air-handler I believe it doubly important that your returns are FULLY DUCTED AND ABUNDANT!!!

    If you do use hydro-air and also use a mod-con boiler, and combine this with daily setback, please, please, please use "smart recovery" thermostats set such that space temperature is FULLY RECOVERED BEFORE MORNING SHOWERS!!!!!
  • Boilerpro_5
    Boilerpro_5 Member Posts: 407

    I am not sure why you say you cannot have much slope for an air handler. I have some running full reset and have been that way for decades. Tekmars reset curve for air handlers is nearly a straight line....no curve, since the output of an air handler at constant air flow is quite linear to the temperature of the water.


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  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
    Cannot Have Much Slope...

    ...and "nearly a straight line + no curve" are the same thing.
    J. WALTER BOOTH Member Posts: 21

    I want to thank eveyone that has responded
    I had all the plans to turn this house into a hot water,radiant home and utilize the duct work for summer a/c and air exchange , then the loss of space for equiptment bothered me. that is the time i considered the air handler
    must of your ideas are the same that i came up with' plus a few more which led me to post my delema.
    as for a full modulating furnace, flame and blower,LUXAIRE
    has had alot of success with there new model FL9C
    this is a spring project so i have all heat season to decide
    any other ideas please throw them this way
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