Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Hydronic Gas heating w Blower - Cold air blowing long after thermostat reaches Temp set

D818
D818 Member Posts: 19
in THE MAIN WALL

Hello Everyone,

I have a hydronic natural gas heating system that is delivered through blower/hvac. I have an Aquastat on the return line set at arounf 150 degrees. After the call for heat is made and the water in pipe goes above the 150 degrees, the blower turns on to deliver heat. The issue I am having is that once the thermostat reaches desired temperature, the blower does not turn off until the the Aquastat temp on return line goes below 150 degrees. This can take 10-15 mins sometimes and will blow cool air during that time cooling down the house.

Does anyone know how I can get the blower to turn off once thermostat reaches temp? Could i just adjust the wiring connections in thermstat? Or is this by design for safety to ensure heating pipes are cooled?

Pics below

PXL_20241118_022237887.MP.jpg
PXL_20241118_022213039.MP.jpg
PXL_20241118_020710397.MP.jpg
PXL_20241118_020648291.MP.jpg
PXL_20241118_020634362.MP.jpg
PXL_20241118_020540965.MP.jpg
PXL_20241118_020552634.MP.jpg
PXL_20241118_020624552.MP.jpg

Comments

  • HVACNUT
    HVACNUT Member Posts: 6,298

    Are you sure the aquastat is on the return?

    Under the cover of the aquastat, on the right side is a differential dial. What's it set to? It should be 10-15 degrees.

    If it's running and you tap the aquastat and the fan stops, it's stuck contacts in the aquastat.

  • D818
    D818 Member Posts: 19

    I am sure the Aquastat is on the return line. The fan does not stop when tapped. I need to double check differential

  • pecmsg
    pecmsg Member Posts: 5,282

    That pipe can stay hot for quite a while.

    Look at TACO fan controller

  • Kaos
    Kaos Member Posts: 184

    The sensor is in the wrong spot. Needs to be right by the coil inside the plenum so it it can pick up when heat shuts off. The other option is to use a simple delay timer to trigger the fan that is:

    -thermostat call for heat→adjustable delay later turn on fan→thermostat call ends→adjustable delay later stop the fan

    Also those are not the best setpoints on the boiler for efficiency. Lot of this depends on how well your coil is sized to your heat load but here is what I have done that works.

    Set the boiler on outdoor reset with a min temp of around 120F max around 150F (max depends on how big the coil is compared to house heat load). Adjust the flow rate through the coil to get as high of a delta your boiler allows, 30F is a good start. If the air out is too cold, reduce CFM. Efficiency is all about return water temps, so you want that as cold as possible.

    You might have to iterate GPM and CFM and max setpoint to get it to work well when really cold.

    Generally you want long runtimes with pleasant not too hot and not too cold air out. The longer the run time with the lower the temps, the higher your boiler efficiency will be. You'll also get much better comfort as the heat will be more even than simply cycling for a couple of minutes blasting you with 160F air.

Categories