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Community and Q&A

Cold air return in basement?

FranWall | Posted in General Questions on

I have a Venmar AVS Constructo 1.5 Heat Recovery unit installed in the basement of my condo. This was already installed when I moved in. I am the first occupant of this condo. There are vents installed on the main floor at ceiling level in the kitchen and in the two bathrooms. There are two cold air returns on the main level. There are heat registers installed in the ceilings of the three rooms in the basement (finished lower level), but no cold air return register on that level. I’ve read through the owner’s manual and researched the installation of the HRV unit on the internet, but can’t seem to find a common answer as to whether, or not, there should be a cold air return on the lower level. Would really appreciate some advice.

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  1. GBA Editor
    Martin Holladay | | #1

    Is the HRV connected to your forced-air heating system? Or does the ventilation system have dedicated ventilation ducts?

    If the system has dedicated ductwork, there are basically two kinds of ducts leading to rooms: exhaust ducts that remove stale air and fresh air ducts that introduce outdoor air to your rooms.

  2. FranWall | | #2

    The system is connected to my propane furnace. I traced back the duct that says exhaust air from building. It goes to a small duct in the lower level bathroom - one I had not noticed before as it's on the wall. The one that's visible in in the ceiling. I'm now assuming the one in the ceiling is for heat and the one in the wall is to exhaust to outside. I found another one off that line leading to one of the upstairs bathrooms. I think I understand how all that works, but if I do understand correctly, those ducts are venting to the outside. I'm still wondering why there is no cold air return directly into the furnace system on the lower level. It is much cooler in the basement during the winter. Would it be wrong to add a cold air return?

  3. GBA Editor
    Martin Holladay | | #3

    It sounds like most of your ductwork has been set up to serve your heating system, not your ventilation system. The HRV was tacked on as an afterthought, without proper ventilation ductwork design. I don't recommend this type of ventilation ducting. Instead, a proper ventilation system should have its own ducts.

    That said, there are right ways and wrong ways to connect HRVs to furnace ducts. Attached below is a diagram from the Venmar installation instructions. It shows fresh air being introduced to the main return duct of the furnace, and exhaust air being pulled from the bathroom and kitchen via dedicated exhaust ductwork.


  4. FranWall | | #4

    I guess I'm not communicating properly. I have that diagram from the users manual and yes... that is the way it's installed. The small intake wall duct in the lower level bathroom goes directly back to the HRV via a separate duct. It goes into the HRV outlet that says "exhaust to outside". The duct in the upper level bathroom is connected directly down to that same duct work just before it goes into the outlet that says "exhaust to outside. From the HRV "intake outside air duct" there is a dedicated duct that goes directly into the furnace's cold air return. All exactly as in the diagram. What the diagram doesn't show (as far as I can see) is how the cold air returns feed back into the heating system. I have two floor cold air returns on the upper level. They both feed back into the cold air return on the heating system. The HRV "intake outside air duct" feeds into that same place. So... 3 feeds to the cold air return on the furnace... two from the upper level floor vents... and one from the HRV "intake outside air duct". My confusion... question... relates to the fact that I do not have a cold air return to the furnace on the lower level. The only return on that level is the wall duct in the bathroom that feeds back into the HRV "exhaust to outside". The lower level is cold in the winter. There's no duct work to take the cold air off the floor back to the heating system. I want to know if that's normal because of the installed HRV system, or did they just not bother installing one. If it will not affect the HRV system,... can I add a cold air return to try and make the lower level warmer in the winter?

  5. GBA Editor
    Martin Holladay | | #5

    Your question is a heating system question, not a ventilation system question. The opening sentence of your original question ("I have a Venmar AVS Constructo 1.5 Heat Recovery unit installed in the basement of my condo") confused me. Now I think I understand.

    You are correct that insufficient return air ducts can lead to comfort problems in a home with forced-air heat. However, the main reason that your lower level is cold is probably either (a) the warm-air supply airflow from your furnace to the rooms on that floor is insufficient, or (b) your house is very leaky, and a lot of air is leaking out of your top-floor ceiling, leading to infiltration of outdoor air through cracks in the wall or rim-joist area of your lowest floor.

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