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Converted from Radiators to Hydronic Coil forced hot air need some expert advice

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Hello all. I am a GC and do a lot of renovation work with vandalized properties for investors. This job was vandalized all the copper ripped out, however there was an existing Central Air unit so it made sense to make use of existing duct work and simply install a hydronic coil on a new air handler. Existing boiler was used, set up the same way it had been with traditional radiators in a loop system. AC Contractor used a clip on stat to register temp at the coil on the Air Handler instead of an Aquastat to save some money, fine by me investors are cheap. Anyway the issue i am having is the water in the feed to the coil is consistently hot without the circulator running, this in turn causes the fan in the air handler to continuously run without the thermostat in the house calling for heat so the circulator isnt running. Boiler is in the basement and the air handler in the attic with about a 25 run between them. I cant figure out why the hot water is traveling up to the air handler with out the circulator running. Any education you can provide would be greatly appreciated. I did test my theory by disconnecting the clip on Aquastat to see if the fan would stop running and it did.

Thanks again,

Pat

Comments

  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
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    First thing I'd look for is a check valve either internal on circ, or in line on the loop. What else is the boiler doing- other heat loops or domestic hot water?
    pattyv525
  • delta T
    delta T Member Posts: 884
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    It sounds like you are either getting gravity circulation from the other zone (the looped radiators) or the pump for the radiator zone is causing flow through the air handler. In either case a zone valve should solve your problem, or if there is one already installed, it may need to be replaced. Post some pics of the boiler and its associated piping, also the piping for the fan coil connection might help as well.
    pattyv525
  • pattyv525
    pattyv525 Member Posts: 3
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    Will do... I am going back tonight the house is 76 degrees fan is running because of the clip on aquastat that is triggered at 140 degrees. There are actually no more radiators just a single zone loop up to the coil at the air handler and back down. Verified the circulator is not continuously running so it isnt the relay boiler is equipped with a DHWC so as the hot water rises up from the basement into the attic and the fan continually blows past the coil cooling the water the boiler continuously thinks someone is using DHW and so the boiler maintains temp and thus the situation never resolves itself even though the thermostat isnt calling for heat and the circulator isnt running.

    Could something as simple as a heat trap work do you think? And i guess just plumb the zone valve right after the circulator it is plumbed in at the feed on this unit?
  • pattyv525
    pattyv525 Member Posts: 3
    edited November 2016
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    Bob Bona just a TACO 007-F5 no flow check put a new flow check when i inherited this hunk of junk. See comment above please and let me know your thoughts. It has to be simple, just amazing to me that the water would travel so far laterally and vertically naturally.
  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
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    What kind of flocheck? Can you get a pic up?
  • Jamie Hall
    Jamie Hall Member Posts: 23,635
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    pattyv525 said:

    Bob Bona just a TACO 007-F5 no flow check put a new flow check when i inherited this hunk of junk. See comment above please and let me know your thoughts. It has to be simple, just amazing to me that the water would travel so far laterally and vertically naturally.

    Ah... no. It is amazing, but if there is a temperature gradient such as you have it will do that. Quite happily. There were a lot of houses which were heated that way!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    delta T
  • delta T
    delta T Member Posts: 884
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    Old style gravity hydronic systems could easily achieve flow rates of 15-20 gpm with no circulators. if there is a density difference water WILL move. Convection is a powerful force :)

    You could install a zone valve on that loop and rewire it so that the zone valve motor is connected to the thermostat, and the end switch on the zone valve controls the relay for the pump to the fan coil. This is the simplest solution IMHO, I don't think a heat trap is going to do the trick considering you already installed a flow check, though that does depend on the kind of flow check. Installing a ZV would probably be less involved than making a trap.