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Furnace/Blower: Rheem R92PA0851521MSA

Dual Zone System (Honeywell TrueZONE HZ311) - Honeywell M847D1004 Actuators

Age of system: less than 2 years old including ductwork

Ive noticed that if Zone 1 is closed, and Zone 2 is open blowing A/C that there is a considerable amount of blowback coming out of the fan/blower area. To the point that the utility room is cold and air gushing.

Ive changed Zone 1's closed position to being partially open (via the actuator range stopper adjustment) and this has reduced the blowback considerable. I have not checked to see if there is blowback when Zone 2 is closed and Zone 1 is blowing - Ill do that next.

Are there other factors that are causing this blowback other than the simple concept that the unit is blowing more volume than the single ducting can handle? Are there better remedies than just not fully closing the Zone? Is this blowback problematic?

Just to be clear, by blowback I mean that it seems that all the air flow that is intended to go up and out the ductwork is too much volume, so it spills out every nook and cranny that it can to equalize pressure.

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This may or may not apply to you, but you have a newer system so there's a better chance of this being the case.

Some air handlers have blowers that can operate at more that one speed, and the zone controller that you have can control these speeds (section in red under #6):

Zone Controller manual

Zone Controller Manual

When multiple zones call for heat or cooling, the fan operates at high speed. When only one zone is active, the fan will run at a slower speed.

I've dealt with a few HVAC techs that really didn't understand all the capabilities of those zone controllers. Some techs just know more than others and may not realize how to hook up a two speed blower properly.

Your next step should be to look at the model number on your air handler to see if it supports multiple speeds.

  • Thanks - this is interesting. The furnace/blower model is Rheem R92PA0851521MSA .. I dont think it is 'Variable' but the blower itself has multiple leads for the different speeds (red = slow, black = fast, etc). Right now cooling is connected to fast, while heat is connected to medium. I could sync heat/cool to be the same -- OR -- I really like your idea that the zone controller could adjust the speed. I need to look into that some more – cgmckeever Jul 16 at 16:09
  • Yea, the connection on the zone controller is meant to go to a similar input on the air handler. The zone controller won't be able to control the high voltage of the fan on its own. If you were particularly industrious, you could probably put together some relays to control the fan speed based on the zone controller output, but that's a little beyond the scope of this site. – JPhi1618 Jul 16 at 16:12

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