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  1. #1

    Hot air/water geo in old home

    Well, bids are coming in to add geo to a 1904 home with hot water heat (cast iron radiators 7 year old cast iron gas boiler) and Unico air conditioning system.
    They all seem to want to hook into the forced hot air (4-5 ton sys).
    Some want to also hook into forced hot water, some say won't get the radiators hot enough to do much. (Prob oversized to some degree due to insulation)

    All want to keep the boiler as backup for the cold MN winters.

    I guess I need about 10ton system to get most of the season.

    Issues: When the dual system can't keep up - boiler will kick in and provide 160-180 degree water to radiators. How will mixing with 110-120 from geo hot water sys help at all? ie will half the system (hot water tie in) be useless for that part of the year?
    Am I better off just getting what I can from the forced air side and keeping the good old comfortable hot radiators when the smaller system cant keep up?
    Anyone happy with 110-120 degree radiators?
    Many thanks. Great forum.

  2. #2
    Join Date
    Jan 2004
    This job is no place for guessing, it should all start with Man J heat loss and find out that the duct system most likely is undersized for the heat load, then realize that the standing radiators at 120 degrees will produce enough heat for Labor Day weekend, then figure out that a return temp to the old boiler has to be above 160 for condensate elimination, of course if the boiler already has primary/secondary loops that problem is solved, but the heat pump will be of no use all winter. Maybe take the big jump and install infloor radiant, if there is enough floor area provide the amount equal to the loss. I'd probably stick with the "old" cast iron boiler, it only has 30 years of service left anyways.
    Class of 70

  3. #3

    Part way there

    Thanks for the reply.

    I know there is some tongue in cheek there.

    All the contractors are experienced and have done heat loss cals/measured the house and radiators and have used my heating data from gas company for the last three years.

    Seems like the hot air will take care of all the heat on many of the days and half the heat on very cold days - yes? So there is benefit from the hot air geo system.

    One has said that the geo hot water tie in will take me to 90% of year round.
    One is not sure, other says doesn't recommend it.... to take the 75% or so coverage from the air tie in and keep the system simple.

    (yes to primary/secondary loops) Don't think there is much guessing, just differences of opinion.
    One thing I know is that the system works now.
    Thanks again.

  4. #4
    Join Date
    Feb 2004
    Pacific NW
    Anyone happy with 110-120 degree radiators?

    Not me, by the time you have another 10F differential in the condensor, your COP will be very poor for a wshp.

    They all seem to want to hook into the forced hot air (4-5 ton sys).

    They is right. (famous 'blazing saddles' retort)

  5. #5
    Join Date
    Jan 2004
    Your right about the tongue in cheek thingee, Sorry I can't help myself sometimes. One thing comes to mind about the forced air system, if there are areas that do not cool evenly nor adaquately they will not improve when heating the same areas and if the boiler is maintaining standby temps you will have a larger stack loss in ratio operating to time for heating season. There are cures for all the ills once they are known and the KISS system is usually the one to use.
    Class of 70

  6. #6

    Not ready for prime time

    Thanks to you both for the replies.
    Well, am I hearing consensus that geo can do hot water for in floor heat but not for cast iron radiators?
    I have come across info that if oversized then radiators may do the trick. Well I just haven't heard of anyone happy with luke warm radiators.
    1- Looks like if I can get all the areas covered, then hot air from unico can get me part way there. (good idea about stack loss, didn't think about that despite the auto damper I have)
    2 - Leave the cast iron beast in the basement alone until they come out with the 160 degree geo hot water heatpump.
    Any new gadgets on the horizon?, (climatemaster 145 degree may not do the job.)

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