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Outside air drawing in the house – second floor ductwork

HhsHwZFSCs | Posted in General Questions on

I have a two-story house in Atlanta, GA, built in 1984.

I have noticed my supply and return registers have some air drawing in them on the second floor. I have a sealed gas furnace, 95% AFUE.

The HVAC vendor has told me the house draws air in as well. I have caulked around all registers and masticed all areas of ductwork and plenum. All my gas appliances are new furnaces (2), Tankless water heater, and gas range.

Question #1. If a house has a “stack effect” why am I seeing this happen?

Question # 2. Should I be concerned about this?

Question #3. Can this allow air to draw in from the plumbing vent pipes?

Question #4. How do fix this issue?

Question #5. Have I air sealed the house too tight?

Any thoughts would be appreciated..


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  1. GBA Editor
    Martin Holladay | | #1

    I'm not sure I understand what you are saying, but it sounds like you are saying that the house is depressurized with respect to the outdoors. (The best way to confirm this is to hire an energy auditor with a manometer and a blower door to run some diagnostic tests.)

    The main questions to ask are:
    1. Under what circumstances does this depressurization occur (assuming that it is, indeed, depressurization)? Is the furnace on or off when this phenomenon occurs?

    2. What exhaust fans are running when this phenomenon occurs? Bath exhaust fans? Range hood? Clothes dryer? Central vac system?

    There are many possible causes of this phenomenon, including an unbalanced forced-air system with leaky ductwork, some of which is outside the thermal envelope of the home (for example, in an attic).

  2. qTxvvHsiEw | | #2

    I have spent many years working with house pressures like what you are experiencing and a couple things maybe at work here just need some extra info. The title of the question leads us to believe that you have confirmed that outside air is entering your home through your ducts? Your explanation sounds like you feel air is drawing into your ducts on the upper level? I assume this symptom which ever it is, is being detected while the AFU is off? Also tell us a little about your existing mechanical fans such as bath fans, kitchen fans, laundry room fans, ERV, HRV etc. and there run times. In addition where is the clothes dryer located in relation to rest of the home?

    Your homes tightness shouldn’t be thought of in the sense of being too tight. There is not really such a thing as too tight. There is however and quite common homes that are too tight for the amount of fresh air ventilation they are receiving.

    Your home is experiencing some pressure curiosities that may be related to thermo dynamics or might be mechanical in nature. Either way you are smart to pursue this issue as only good can come from what you will learn about your home while investigating.

    If you tell us a little more about the conditions that are present during this event I am sure I can lead you in a proper direction to further investigate.

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