In the picture below 1 and 2 are the two large air returns (they are at floor level)

2 corresponds to 4 and 5 which are openings in the return duct !

1 is a large register it spans the space between two joists BUT it does not communicate with the air return. It corresponds to 3 which is just a duct that lands at floor level in the basement

It does not make any sense because if you look under the floor from point 1 you can see the air return duct …
I think somebody cut some corners and did not complete the job to connect the air duct that goes down to basement to the main return

enter image description here

here is another angle for that duct that goes between the main floor and the basement without connecting to anything else

enter image description here

1 and 2 look like this enter image description here

Here you can see the return duct that has no opening in it enter image description here This is the picture of the second joist space where you can see the lip of the duct shoe that starts #3, it goes vertical from that point, while the camera looks horizontally toward the return duct enter image description here

  • what did you use to make the cad drawing? Commented Sep 7, 2022 at 5:20
  • Is your house 2 levels, basement and main floor or more than that? Commented Sep 7, 2022 at 5:21
  • I used Sketchup for the 3d rendering. It is ground floor and basement.
    – MiniMe
    Commented Sep 7, 2022 at 8:55

2 Answers 2


To answer the titular question of "why it's this way", either:

  1. Perhaps someone stopped work to ask whether or how to connect both 1 and 3 to the trunk and forgot about it.
  2. Get out your crystal ball because you'd have to read the minds of them what done it.

If 1 and 3 are in the same joist bay, then the bay itself is the return duct, and this was simply a short cut method to save on some sheet metal.

It seems that the same situation happened with 2 and 4/5.

Would it have been better if they'd connected the openings with sheet metal? Probably, but if your HVAC system is working, well, then, it works.

This answer was posted prior to the addition of the "no duct in the air return" picture (currently the last pic in the question), and, frankly, from the description and drawing, it was unclear to me exactly how it was laid out.

Based on this recently added picture, the simple solution (presuming the in floor picture shows the return air duct), might be to gain access to the side of the duct (cutting up through the ceiling drywall, not down through the hardwood floor), then cut a hole into the duct. Patch the drywall and call it a day.

  • well I am not sure how well it works, after seeing this crap I do not think that is anywhere near adequate. Practically the only real return is #2 where the air is getting directly into the return duct. There is one small return in one of the rooms in the basement, just below that and that is is for the entire house. I think that the air circulation in the basement happens mostly based on the pressure generated by the furnace/ac when they push fresh cold or hot air in the basement. That will move the existing air toward one of the ends of the basmenet when the access to the basement
    – MiniMe
    Commented Sep 7, 2022 at 13:53
  • just to be 1 has no connection with the duct ...I will upload two pictures taken under the floor across the two joist spaces that 1 covers
    – MiniMe
    Commented Sep 7, 2022 at 13:55
  • The hardwood is being removed so theoretically I could remove a couple of boards just above that area and do the duct work that I need to do. What I need to understand is why it was built like this and why they did not open that duct there which would have been very easy for them intially
    – MiniMe
    Commented Sep 7, 2022 at 16:38
  • In that case, go for it from above. As to the why, either the first paragraph of P2000's answer or get out your crystal ball because you'd have to read the minds of them what done it. I think the general consensus is that this wasn't done correctly.
    – FreeMan
    Commented Sep 7, 2022 at 16:56
  • 1
    @FreeMan good point, feel free to add that into yours without attribution
    – P2000
    Commented Sep 8, 2022 at 14:25

I think that adding one off these at the bottom end of 3 will solve my problems. I will hook that to the home automation system together with the HVAC https://www.homedepot.ca/product/power-air-square-of-round-ducts-air-booster/1000509032

It turned out that what I am seeing in the pictures (last two)is no the cold air return but some extension of the supply. The cold air return should be closer AND I think what I am seeing is in fact the supply duct. I am not sure why it is now elevated in the floor, it does not make sense because it would mean the joists have been cut there. I think those are just there to block the air to go further deep under the floor.

Update: since the floor was removed and I am left only with the diagonal boards I took a long knife and I started testing to see if there is duct under the floor behind those metal sheets you see in the picture. There is nothing there, they were installed just to block the air from going under the floor (way too far if you ask me) So the only option to improve this design is to install the above

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