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Want central A/C in a circulated hot water house

I just moved into a modest 1917 colonial here in Michigan (after living in the north-east all my life) and I have a standard gas fired hot water boiler and circulating system with a combination of standard baseboard units in some of the rooms. But in the main spaces (bedrooms, dining room, kitchen) I have hydronic fan coils, i.e., when the thermostat calls for heat, not only does the boiler come on, but also does the fan in each of these units blowing air over the hot coils in each room.

I would like to have central A/C, but since I do not want the expense of running air ducting for a central air unit, I was wondering if I could install the air conditioning compressor unit with a heat exchanger that uses the water in the boiler to circulate cold water to the hydronic fan coils in the summer time.

Has that ever been done? Would it work? Would you think local heating/cooling specialists be able to accomodate this request? Thanks.


  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380

    Yes, TJ it can be done...

    What you would need is a smaller chiller, which is an air conditioning system that cools water instead of air.

    Your best bet would be to puchase a packaged chiller, which would not require the running of refrigerant lines, as all of the piping is factory installed.

    Your piping arrangement for the "fan-coil" units would be set up so that chilled water would circulate freely through the coil in the summer months and the fan would be controlled by the thermostat.

    What you are referring to is basically and constant flow system, where chilled water is circulated in the cooling months and heated water is circulated in the winter months. This configuration is very common in hotels.

    The system would require a manual changeover, though, between the winter and summer months.

    In the winter months, the chiller would be valved off from the main loop and the hot water source valve would be opened. It's a rather simply piping set up, but it should definitely be laid out by a company who has experience with chilled water systems.
  • bob_50
    bob_50 Member Posts: 306

    watch out for the condensate!
  • Eugene Silberstein
    Eugene Silberstein Member Posts: 1,380
    Of Course...

    I would hope that the contractor who would be laying out the job would take that into consideration as well as other factors such as variable blower speeds and a means to eliminate or reduce the natural convection currents when the thermostat is satisfied in the heating mode.

    Keep us all posted...
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