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Hydronic heater thermostatic fan control

pblantonpblanton Member Posts: 3
I picked up two new, unused hydronic heaters from a guy on Craigslist for $100 ($50 ea.)

I got a Trane and a McQuay. The McQuay was made in 2002 and I just connected it to my boiler this evening. The Trane will go in my garage sometime later.

I installed a simple thermostat in the room and connected it to the Taco controller for the zone that runs the McQuay. The McQuay is the only thing on the zone.

Most everything works as expected (thermostat calls for heat, the boiler fires if necessary, the zone valve opens and the core of the McQuay gets warm.) I expected the fan on the McQuay to respond to the temperature of the core, such that when the heater heats up, the fan comes on until the water stops running, thereby allowing the fan to cool the heater to a point at which the fan stops.

Unfortunately that's not how the fan works. The fan has a knob inside a small panel, that turns it on and adjusts the speed. it is NOT thermostat controlled at all. Currently I am leaving it on all the time, but want it to cycle with the call for heat.

I'm thinking that the Taco controller in conjunction with a little 24v relay will solve my problem.

Another option is a 24v transformer and relay, mounted inside the McQuay and a separate wire from the McQuay to the thermostat so that it can directly control the fan alongside the call for heat.

I'm also not opposed to the idea of putting a 24v transformer and relay along with a an adjustable thermal switch inside the McQuay so that the fan responds to the core heating up like I described.

Any help with how to proceed, and how to wire it up would be most appreciated.



  • HVACNUTHVACNUT Member Posts: 3,369
    Probably the easiest way is to install a single zone switching relay at the heater and use a Snap Disc, close on temp rise thermostat strapped to the return heat pipe.
  • SuperTechSuperTech Member Posts: 1,336
    Use an aquastat strapped to the return line coming out of the unit to cycle it when the coil heats up.
  • hot_rodhot_rod Member Posts: 13,318
    kickspace heaters just use one of these snap disc clamped to the coil piping, run the fan power thru it. You can buy adjustable versions also. Two types a F and L version, the L is limit and opens one temperature rise. You want a F, which makes on temperature rise, breaks when hw supply stops.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • EdTheHeaterManEdTheHeaterMan Member Posts: 572
    edited March 18
    This should make it easier
    assuming you have a McQuay model UH

    Here is the part number of something that will work

    here is the sheet for a McQuay UH
    copy and paste this to your browser.

  • pblantonpblanton Member Posts: 3
    Thank you so much everyone!

    I have just left the fan on low, but it makes an annoying buzz when the heater is cool. It's very quiet when the heater is warm, so I'm looking forward to executing the plan.

    Thanks again!
  • EdTheHeaterManEdTheHeaterMan Member Posts: 572
    edited March 30
    @pblanton said, "so I'm looking forward to executing the plan."

    Good luck to the Executioner! :o

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