Return on an outside wall! Keep it, or shut it off and insulate the bay? Help?

Discussion in 'HVAC Heating & Cooling' started by lithnights, Jan 31, 2010.

  1. lithnights

    lithnights New Member

    Messages:
    143
    Location:
    PA
    Hello all,
    This site is the best, so I'm hoping someone can help me out with a major problem I just discovered with my forced air HVAC system.

    We've done major reconstruction over the years to our home which involved rerouting of supply and return lines. This rerouting was often not done in a very efficient manner.

    My recent discovery was that our HVAC guy created the return in one of the bedrooms, on an outside wall. The old return ran through a downstairs wall that was moved so he moved the return. Unfortunately, for the new return, he basically just removed the existing blown insulation and used the stud bay as the return. Thus, between the bedroom and the outside air is just the grill, exterior sheathing, layer of the old shingles, and the siding. Even worse, some of these materials are cracked/broken to the point where last night I could even see a glimpse of my neighbors light from the bedroom. No doubt I am losing tons of warm air to the outside. Not good! I taped up the pinsize hole and cracked areas with a good mastic tape but it's still a bad situation.

    Thus the question... is it better to leave it as is which means I have a return but an entire uninsulated bay which gets directly hit by the NW winds we get OR better to close off that return and fill the bay with insulation?

    I know an efficient forced air system relies on the returns but it pains me to be throwing money away in heating costs with such a huge uninsulated bay which allows air flow to and from the room via the return grill.

    I am attaching two pics. The first is the grill. The second is the view from the outside. The uninsulated bay runs along that narrow vertical piece of the house. See my artistic red lines. You can see the bedroom window to the left.

    Thanks in advance!

    Attached Files:

  2. dlarrivee

    dlarrivee New Member

    Messages:
    1,172
    Location:
    Canada
    That's absolutely terrible.

    What sort of return air is in the hallway outside this room, or near by said room?

    You should have a return for every supply in most cases, but not having insulation in an exterior wall sort of negates the purpose of heating your home...
  3. lithnights

    lithnights New Member

    Messages:
    143
    Location:
    PA
    The hallway is basically a 6x8 area with 3 bedrooms and a small bath shooting off of that area. The two bedrooms (other than the one in question) each have a working, undisturbed return; the bath does not, the hall does not. So basically, if this return gets shut, the chances of getting return air out of this room will not be good. Not ideal. But again, like you said, neither is having such a direct route to the outside air.
  4. dlarrivee

    dlarrivee New Member

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    1,172
    Location:
    Canada
    I think that it must be possible to create a better path for this return duct.

    What is below this room? I find it strange that there is no return in the hall area, is there a supply there?
  5. Hube

    Hube New Member

    Messages:
    156
    Location:
    Ontario
    A return serves BESTwhen installed on an interior wall, but an outside wall is generally ok as long as the passage is fairly air tight or insulated.In your case it is not the best because of this leakage to the outside. Since this a "high" wall return, you could cut the opening in at the FLOOR LEVEL,thus eliminating any leakage from the higher areas of this return passage. As long as the rest of this return air passage is fairly weather-tight you will be ok
    .Note; return grilles serve best when located at floor level in the heating season, and best at the high level when in the cooling season.. but at least just having one in the room either high or low will certainly be of great help.
    if it was my home I would cut in an opening at floor level (in the same stud cavity), blocking off the upper passage, and make sure the remaining return air passage is reasonably weather-tight. If this proves to be too much work, then you could just under- cut the bedroom door an inch or so to allow any return air to be picked up by another return near this bedroom area.
  6. lithnights

    lithnights New Member

    Messages:
    143
    Location:
    PA
    No supply nor return in the hall. That was the original build. Below the room is a kitchen, a wide open eat in kitchen with no place to do the return. That was why the HVAC put it where he did. It was a small closed in kitchen. We busted through a wall that contained the supply (now rerouted) and busted through a wall that contained the return. Looking back, if I had known what I know now about HVAC, we would have rethought the whole idea..
  7. lithnights

    lithnights New Member

    Messages:
    143
    Location:
    PA
    Wow, a great idea..I totally can envision what you're talking about and it'd probably only take me an hour or so. The only problem is that the bottom 3 feet or so of the wall is covered by wainscoting I installed 4 years ago. I COULD cut through it and put a low return..I'm just not ready for the punishment that my wife will give me for messing up the wall. haha.. Maybe it won't look so bad. Even if it did, I think I'd be best to give up aesthetics for functionality (and big energy savings). If that wainscoting wasn't there, I'd go start the job now.

    I agree about utilizing a high return in summer, floor in winter. We actually have a high and a low in our master which I swap covers depending on the season. I installed the high a couple years ago. Again, the wife is not thrilled with multiple holes in the wall so I never did the other rooms.
  8. Hube

    Hube New Member

    Messages:
    156
    Location:
    Ontario
    Well, it's either cut into the wainscotting (no big deal) or put up with the drawing in of outside air.And that room must be having a great deal of heat loss in the heating season and also a great deal of heat gain in the cooling season because of the way the wall is not well (if any) insulated and also because you claim that you can see outside thru the gaps.
    Btw, another idea, if it is at all possible, would be to install a return at the FLOOR, intersecting this wall passage. Simply cut in a opening for a grille in the FLOOR right in front of this existing wall passage. Make sure you install a block end in this JOIST space where you cut in the new floor grille .
    Doing it this way, the return air will now be now drawn from the floor level instead of into this leaky wall passage. Savvy?
    And you won't even have to cut thru any wainscotting either. hooray1
    If you have any more questions on this, just ask. Hube
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,126
    Location:
    New England
    I would definately look for an alternate path. The dew point in there would likely mean in the winter-time, you'd get condensation and probably frost accumulating on the outside wall. This can lead to all sorts of problems, including health, not counting the energy loss.
  10. dlarrivee

    dlarrivee New Member

    Messages:
    1,172
    Location:
    Canada
    I forgot to mention that part of it.

    There is no insulation, and having this all open destroys the continuous vapor barrier that you SHOULD have.

    My biggest concern here is the lack of vapor/air barrier, which means you'll eventually start growing mold on the inside of your sheathing.

    What you could do, but would be quite expensive, is have a spray foam guy put an inch of foam on the inside of the sheathing and the inside of the two studs so that it will tie into the existing (I hope) vapor barrier.

    You'd still have your duct, albeit a smaller one, but it wouldn't be a breeding grounds for heat loss and mold.

    More important than thermal performance of the insulation is AIR sealing the building envelope.
    Last edited: Jan 31, 2010
  11. Hube

    Hube New Member

    Messages:
    156
    Location:
    Ontario
    after really thinking about this problem (if it were mine) and also would be very inexpensive too, would be to cut in another FLOOR opening that will intersect this existing stud cavity and install a FLOOR return grille,making sure that the old passage is blocked off. Then in order to make the room more weather-tight I would have insulation injected /blown into this proplem wall (foam or celluloise material)
  12. lithnights

    lithnights New Member

    Messages:
    143
    Location:
    PA
    Now that may be even a better idea than the low wall return..IF there is no joist between the current return line and the future hole in the floor. One concern (for either) is that in the future, I'd be limited by what kind of furniture to put there.. i.e. couldn't put a large dresser over or in front of it.. Off to talk to the wife to get the aesthetic preference...
  13. lithnights

    lithnights New Member

    Messages:
    143
    Location:
    PA
    Hey Hube,
    Maybe I'm confused (not surprised), but isn't this the same solution you advised yesterday Jan. 31? Seems to be the same idea except now you are suggesting to block off the old passage and insulate the old vertical chase (which is what I assumed you meant originally). Agree?

    Thanks for the ideas!
  14. Hube

    Hube New Member

    Messages:
    156
    Location:
    Ontario
    Yes, it is pretty well the idea same as I posted earlier,but with the added fixing of the problem wall.And if you do cut in this new floor return you shouldn't have no joist in the way because the old existing route would surely be in between the joists.
    And even if by chance there was a joist in the way, then you would merely have to block two joists instead of one.A floor return grille is quite flat (no damper parts) and sitting over a joist would cause no problem.
    Just make sure these joist passages are blocked off to enable the return air to follow the same path as it did to the intake fan (furnace)
  15. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,126
    Location:
    New England
    One thing to consider with any 'run' that goes from floor-to-floor in the house is that it is a channel for smoke and fire to more quickly advance if not protected in some manner. While stud cavities are used for a return 'duct', I prefer to encase them in metal ductwork that won't support flame. Not much you can do about smoke unless you put a sensor in the air stream to shut the blower motor down if detected. Normally, the codes go to lengths to put in fire stops in the walls to prevent this from happening. Arbitrarily creating a nice open channel without any other safeguards just seems counter productive, especially when combined with the energy losses when on an outside wall and no insulation.
  16. Hube

    Hube New Member

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    156
    Location:
    Ontario
    To whom it may concern; Wooden joist spaces, wall stud cavities, etc are used for the Return air passages in millions of homes in N. America without any problems.
  17. Dana

    Dana In the trades

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    Without knowing what climate zone this building is in you can't make any blanket statements about whether it should have a vapor barrier at all, or where it should be placed. What's good practice regarding vapor control north of the 48th parallel isn't necessarily true south of the 38th parallel.

    But for sure air sealing is important everywhere, and this looks like a disaster.

    Where is this place? (This duct routing approach wouldn't have been allowed a building permit or passed an inspection in any place I've ever lived/worked.) Got a zip code?

    But independent of climate zone, blowing it full of dense-packed celllulose and cutting in a floor return grill seems like the right solution. Using the great outdoors as your return plenum never works in your favor. Have an insulation contractor assess the rest of it too, for both insulation and air-tighness.
  18. Dana

    Dana In the trades

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    True, but many/most would fail the duct teakage standards in CA Title 24 (unless great care is taken to caulk every seam and penetration) and...

    ...using an EXTERIOR wall cavity for the return creates a huge breach in the thermal envelope of the structure, and in some climate zones will create mold conditions several months out of the year.

    Interior stud & joist cavities have far fewer issues and are quite common, if not always best practice.

    I imagine only in areas with relatively low heating loads would anybody try to get away with using an exterior wall cavity as a heating system duct. 10-15 square feet of uninsulated wall without even the cavity as a thermal break represents a significant heat loss in 7000+ heating degree day climates, but in 2000HDD climates, not so much.
  19. dlarrivee

    dlarrivee New Member

    Messages:
    1,172
    Location:
    Canada
    So wait a minute, you think that a vapor barrier isn't required just because it's warm outside a lot of the time?
  20. Hube

    Hube New Member

    Messages:
    156
    Location:
    Ontario
    Vapor barrier is always needed but as to where exactly depends on the climate of the area of where it is to be installed.
    A vapor barrier always goes to the heated or warm side of the insulation.In a cold weather climate, it will be on the face of the studs just before the drywall.
    In a warm weather climate, it will be on the exterior side of the stud wall.
    Last edited: Feb 3, 2010
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