Vents blow cold air at end of heat cycle, normal?

16 years ago

We have hydro-air in our house. The master bedroom is on the upstairs zone, but it is separated from that zone by a mechanical damper (is that the term?) with its own thermostat. When the turn the thermostat up, you hear the air handler click on and then a minute later you get warm air until it is up to temperature. But then it blows cold air (cold enough that it wakes DH up) for what seems like at least a minute. Is this normal, that it blows the cold air? Is there a way to alter it so it just stops when it finishes blowing warm air? The vents are on the upper walls because the room is above the garage, so the cold air blows right down on us. Thanks.

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Comments (6)

bus_driver
16 years ago
The fan control on your furnace shuts off the fan when the heat exchanger temperature drops to the preset level. Most such controls are adjustable. Setting it to stop at a higher temperature will reduce the operating efficiency of your system system a bit. Extracting all the residual heat possible from the heat exchanger is desirable to minimize heating cost. Setting the fan control to stop higher than about 85 deg. will increase the heating bill. Setting it at 100 will end the "chilly" blast. Choose your poison.
sue36
Original Author
16 years ago
Bus Driver,
We don't have a furnace, we have a boiler. Would this setting be on the air handlers instead?
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mr_havac
16 years ago
"We don't have a furnace, we have a boiler."
You saved me the trouble sue of explaining that!
OK, what you have is an aqua stat that controls the fan in your air handler. When the t stat calls for heat either a pump comes on or a zone valve opens downstairs and allows 180 degree water to flow through the coil in your air handler. On the hot water pipe that leaves the coil should be a thermostat attached to this pipe. When it senses the water is hot enough going back to the boiler it brings on the blower. That thermostat, known as an aqua stat should be set at 140 degrees. Thats the temperature the fan comes on. The fan off setting is usually 100 degrees. Yours is probably set to low. Check the aquastat settings, there may be 2 settings (on and off) or there may be just 1 and a differential. If its that one set it at 140 with a 40 degree differential. The nice thing about a system like yours is you can fine tune them. If 100 degrees feels to cool you can tweek it up a few degrees to find something more to your liking. You don't have to worry about overheating the equipment. Just don't adjust the two settings to close together or else the blower my cycle on and off to ofter before the t room stat is satisfied
sue36
Original Author
16 years ago
Thanks. I'm going to have DH read this and hope he can figure it out. I was hoping it was something adjustable. The odd thing is I don't think the other zones do this. But the master bedroom is the only zone controlled by a damper.
mr_havac
16 years ago
That could be a who different ball game. Lets see if this simple fix does the trick first and we'll take it from there. In the mean time I'll be thinking of how they might be controlling a single zone through a zone damper. Maybe there's an end switch on the actuator or something. Keep us posted.
sue36
Original Author
16 years ago
Maybe I didn't explain it well. On the first floor we have one zone, controlled by one thermostat and there is one air handler in the basement. For the second level there is one air handler in the attic and there are two thermostats, one of which is in the master bedroom. I was told the master bedroom "zone" is controlled via a mechanical damper. The way I thought it worked (in my non-mechanical mind) was that the thermostat called for heat and the damper would block off the air duct that feeds the rest of the second floor, thereby only sending heat to the master bedroom. I do remember that when this was all installed they forgot about the master bedroom and had to have the HVAC guy come back and add the piece to separate the master bedroom.

Vents blow cold air at end of heat cycle, normal?

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Vents blow cold air at end of heat cycle, normal?

Comments (6)

bus_driver

sue36Original Author

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mr_havac

sue36Original Author

mr_havac

sue36Original Author

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sue36
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