Add downstairs air return?

17 years ago

I'm in northern California and we just completed a whole house remodel. Our old 40 yr old one-story house was about 1550 sq ft and on a hill; the two-story addition built out the side and a lower level to about 2550 sq ft total. The existing air return is 12" x 24" near the ceiling on the top level, and there is no air return on the new lower level.

Is the existing air return sufficient for the larger house? SHould we add a return at the lower level?

To keep the budget down, at my request we kept the 15 year old, 100K BTU, 80% efficient Amana furnace. It's at the same floor level as the new downstairs level. The ducts running out to the rooms were replaced with new insulated ones and extended to new areas. The return duct was the existing one, and is a 16" dia round vertical one; it looks like at some time in the past another 8" dia round duct was spliced out the side of the 16" pipe, then drops down and reconnects right before it enters the furnace.

I'm not sure if the 8" spliced-in duct is really adding to the volume of air return, and it could instead easily be connected to the adjacent laundry room wall for a lower floor air return?

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Comments (3)

ryanhughes
17 years ago
I hope that's not the only return... doesn't sound like enough to me. Does the furnace operate sufficiently? If you added any air supplies to the new addition, you definitely want to put some returns in. In fact I would add more return air regardless. Probably want to get a good contractor out there to evaluate your ductwork system.
wwu123
Original Author
17 years ago
That is the only return.

I think the furnace is operating OK, and is probably oversized. Right now in January, it's taking about an hour in the morning to bring up the temp from about 62 to 68 deg; the rest of the day, it only comes on for a few minutes per hour.

Are there any specific symptoms I could look for to conclude the return is insufficient? The air pressure at the existing return is quite strong; it would be hard for me to pull out the filter while it's running. There is an audible whooshing sound there (granted I'm standing right above the furnace); today's newspaper front page section - 22 pages - will stick up to the grille no problem.

The air pressure at 90% of the supply vents is quite solid though; if the flow doubled it would be practically a stiff breeze. I have a temperature sensor on each level and when the heat is running both levels are within 1 degree from each.

The only really problematic vent is a new downstairs office room. It's actually another 3' lower than the downstairs, the vent is in the ceiling, and it's got the longest duct run (last split on the main duct, then 90 deg turn and another 20' of flexible duct run from the split). There is no discernable airflow or warmth at that ceiling vent. It's only because of this room, that I'm actually partially closing several registers on the top level to try to get more warm air into that one room.

Since all the new supply ductwork is finished and sealed up in the walls, if the main fix I'm looking at is to add another return, wouldn't it be cheaper just to do it than to do an evaluation? It's literally 8" to connect the downstairs laundry to the existing return duct. Is there harm if it's not needed - such a thing as too much return?
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ryanhughes
17 years ago
I would be careful with a laundry room return, for reasons such as lint and chemical odors, etc. More return air can improve the airflow throughout the house. Air needs a return path. The fact that your system only runs for a few minutes along with other described systems suggests that your system is oversized and starving from return air--bad for efficiency and longevity of the equipment. Having an evaluation done and having a professional do the work would be optimum if you were to have the return air tested for static pressure (air resistance) and determine that you are getting the required CFM (proper amount of airflow). There's no doubt in my mind the return air side of the system needs some work, based on your description.

I am not an HVAC professional. There are some here who are, however, so I'm hoping they can also give you more input as to what the best course of action is. There is one site, hvac-talk.com, that also has professionals willing to give advice, as long as you don't mention DIY work, which is frowned upon there.