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adding an indirect

jim f
jim f Member Posts: 182
just wondering...
i just did a heat loss on a house from 1800's at 2836 sq ft. my idea is to provide a 2 zone hydro air system with an air handler in attic and an air handler in basement. my heat loss was 128,000 with safty factor looking at 155,000-160,000 btu.
if i wanted to add say a 40-50 gallon indirect on to the boiler how would i up size my boiler capacity.
thanks in advance.
jim franze tri-city heating and cooling milford,ct.


  • I wouldn't.

    You have what we call "load diversity". If you prioritize the DHW, you should be OKay. Make sure your priority has a time override function. Don't want to freeze up a house because a zone valve or zone pump has failed...

  • jim f
    jim f Member Posts: 182

    the client has a 80 gallon utility rental and wants to incorporate the hater heater in my total bid. would it be sensible to install a water coil scince thier are only 2 people in the house.but they want to monderize thier heating and cooling system for resale value. would you go indirect - coil - coil with storage tank - seperate oil hot water heater??
  • kevin
    kevin Member Posts: 420

    a doubt...indirect(Superstor, phase3 and the such...) kpc
  • Hows the water

    coming into the house ? Ive got a 5 gpm coil in my boiler and its been putting out nice , steady hot water for about 6 years . Only 1 bathroom though . If its well water , I wouldnt try a coil . Good luck Jim .
  • jim f
    jim f Member Posts: 182

    if i went with an indirect how do i calculate the load. is there a spec sheet on how much a say hl45 tank would consume off the boiler. im trying to price it out as an extra and need to know what size boiler to price?
    thanks jimf. by the way ron, it is city water, here in milford the water is decent.very old house with 1 full bath, 1 1/2 bath and 2 - 3 people
  • Steve Eayrs
    Steve Eayrs Member Posts: 424
    You don't need to add

    the dhw load to the boler sizing on this if you will do it like ME said. When the dhw calls for heat it will run as priority and shut down the heat for the 10-15 min. time that the dhw is calling. Their are a lot of controls out there to do this, with some of the dhw tanks capible of it, with their builtin relays, etc.. If no controls on the tank, you might look at a Goldline (i belive its a 34 something model?). Great control.
    The btu load is based on the tank you use, and how many btus the coil or heat exchanger can soak up. 100mbtu can heat a lot of domestic water for a house like this, which means that except for the very small portion of the year, that your house is call for all the heat your boiler can give out, you would not even need to prioritize the dhw.

    A side note; your house must be very poorly insulated to have this large of a heat loss. It may be well worth it to look into insulating it better, if possible, and size the boiler smaller.

  • Bill Riordan_3
    Bill Riordan_3 Member Posts: 31

    Not a good idea to run priority DHW on a hydro air system.Blowing cold air could be a problem depending on type of air handler and wiring configuration.

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  • I would say...

    if you have cold air blowing, its not a source of supply issue, rather an issue at the point of use. If the FCU were properly wired and controlled, DHWP shouldn't cause any more issues than it would with any other method of heat delivery.

    You have to look at the system as a WHOLE, not as a hole...:-)

  • Bill Riordan_3
    Bill Riordan_3 Member Posts: 31
    I agree

    Mark, I fully agree with you. However, my experience is control wiring seems to be a weak point in the trade.But oversizing a boiler for poor wiring skills is a shame.

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  • If it is

    a true priority system, it should totally disable the hydroair; also, the fan shouldn't even come on until the water reaches a certain temperature, say 140*.

    We also do not increase the size of the boiler when there's an indirect. It would mean that you have oversized your boiler for your heating system and it will sort-cycle. As far as a recovery rate, check with the manufacturer of the indirect; they will have tables that tell you how quickly the water will heat as a function of boiler input. Just make sure you use the IBR output of the boiler, not the input.

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  • jim f
    jim f Member Posts: 182

    thank you very much for the replies
    jim f.
    tri-city heating and cooling
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