How to seal AC (only) ducts in winter
moltenmetal
| Posted in Energy, Heating & Insulation on
I’m getting ready to install comfort cooling on the top floor of my radiant-heated home. We’ll use this at most 2-3 months per year.
The air handler and ducting will (unfortunately) go in an unconditioned attic space. The thought of punching all those holes high up in my nice, tight insulated barrier against the cold Canadian winters still makes me nervous!
Yes, I’ll seal and insulate the ducts carefully and thoroughly, but what options do I have for sealing off the supply and return grilles in an attractive but AIRTIGHT fashion during the heating season?
As always, the recommendations of this exceptional group are highly appreciated-
Replies
Bump - you are falling off the list and this post will move you up again.
There probably is a "good way" to do this. Obviously, needs to be easily reversible / removable.
Maybe a couple layers of 2" rigid foam laminated together and fitted into the registers / returns -- sealed with some compressible foam around the edges?
Hopefully someone who knows a better way will chime in.......
Jim
Edit: I just caught that this is a new installation - there may be a very good way to accomplish this provided it is planned for at the initial installlation - the HVAC guys will know.
Edited 5/29/2009 9:39 am ET by JTC1
I found a sign company that made magnetic signs for cars and trucks, bought some of the magnetic stock from him, cut it to the grill size and painted the same color as the walls. When you want to close it off stick the sheet on the grill.
THAT is a great idea! Completely out of the way when not needed, and a nice tight seal!
I was thinking of hinged decorative door covers for each grille but thought somebody out there might have a ready-made solution. Still open to suggestions!
I considered the Unico and the other brand of high velocity systems and no, there's no way I'll be buying that stuff. WAY too expensive- parts cost alone is totally prohibitive. We'll be perfectly happy with AC on the top floor only, so we can fit conventional low velocity ducting in the attic. If some future owner of our home (i.e. after I've moved six feet under and no longer care!) wants to put AC on the ground floor, they can put in a separate split unit.
I scratched my head for awhile until I came up with the idea. We are in Fl and when I had the A/C installed (13 years ago) everyone was putting in supplies in each room and one return in the door of the air handler closet. I had the supply runs put in the ceiling and run to the outside wall and the returns on the inside wall, but to make it seasonally more efficient I have a return at the top of the wall and one at the bottom of the wall. In the cooling season I cover the bottom grill and when I am heating I cover the top grill. I found the magnetic sign stuff really works well. Good Luck
I have the benefit that my forced air system will be cooling only. The attic install sucks due to loss of cooling in the ductwork, but I do get to put the supply ducts up high where they should be for cooling. My return is also ideally located.
I was at my local big box store looking at the plastic supply diffusers that fit a 6" duct. They have a threaded deal on them to allow you to adjust their % open, and they do seem to close pretty tight. Since my drops will be 6" duct, these would seem not a bad solution for the supplies. I really like the magnetic sign material idea for the return grille, except that there's a fair bit of area to it. I'd prefer to have say 2" of foamboard in my cover rather than just something to stop the air leakage. Maybe the magnet material would hold that up, or maybe I'll go with a whole bunch of Lee Valley rare earth magnets to make sure!
Why not use a piece of Astro-foil or Reflectix cut the same size as the grill opening and then use the magnetic material that is the same size at the outside dim of the grill. Get about R-5 in a static situation.
Have you thought about using a high velocity system like Unico properly designed so it doesn't whistle? The you just could slip in a friction cap over the small ducts.
Although I do like the idea of using magnet material to cover the grates - fast and easy.
--
"Though I don't think" added Deep Thought "that you're going to like it."
I have the same heat and a/c setup but when I had the A/C installed I had the mechanic install the filters in the returns. So when I turn the A/C off for the season I put in 1" foam board & toss the filters. It's a 2700' ranch so there are only 2 ceiling returns that hinge down.
For steel registers, I've seen the sheets of magnetic plastic sold for this duty, or you can apply magnets to a suitable sheet of plain plastic. The stuff can then be painted or overlaid with wallpaper.
Sealing the ducts is trickey, any warm air that gets in there during the winter months will condense out moisture.
I'd put the time and energy in insulating the ductwork and leave the vents open.
Hi moltenmetal,
The air handler and ducting will (unfortunately) go in an unconditioned attic space. The thought of punching all those holes high up in my nice, tight insulated barrier against the cold Canadian winters
Brainstorming.......
1. Fully insulate the attic itself with the focus being on a radiant barrier toward the outside......limit the heat that can radiate into the air handler area and on into the interior.....it'll also give a tiny bit of assistance in reducing winter heat loss.....not much....again this type of insulating would be primarily to benefit summer.
2. With your milder summers and limited use, how about simply putting a ducted wall unit......not sure of your floor plan......but putting a single "supply" on each end of the house with a single small return in the center. This would minimize the number of penetrations.
I'm in central NC and we used a single window mounted 5000 btu window AC in an upstairs south end bedroom while we were finishing our home....after it was insulated.....ran it 24/7 with a 22" box fan set in the doorway to move air throughout the 4600 sq ft......the humidity was completely controlled and the house never got over 80 f. the whole summer.......nicest construction job I've ever worked. Point is if we could have half decent temp control in an area with extra humid 90+ ouside temps, you should be able to have the same with very little equipement considering your description of your current insulation package.....granted a million things can affect that such as where trees are, type of roofing etc. but this is simply a brainstorming start....
Pedro the Mule - Like my creature comforts
We seriously considered putting a centrally located split unit in rather than using a conventional air handler and ductwork. Unfortunately, although it would be inexpensive, far less labour and probably would do a great job on the dehumification, it would leave the worst insulated south-facing room (my daughter's bedroom) without adequate cooling.
We had an AC pro in for a quote, and he was recommending multiple split units ($$$)- probably because his cost to install ductwork would be prohibitive. Not so for me- as long as I get in the attic in June before it gets roaring hot.
I'm pretty confident I can do a good job of duct sealing and insulation. But I definitely WILL be sealing both the return and the supplies in winter. Even with a lot of insulation on the ducts, there's a huge surface area in that ducting and the ducts are definitely big enough for fairly large natural convection currents to get going.
Unfortunately, conditioning that entire attic space would leave me with multiple vapour barriers- and a HUGE job.
Ok, everyone else's idea is great. I like the magnetic sign idea too. But............It will still leave an uninsulated hole in the wall the size of the diffuser. Take a trash bag that is a size you can stuff some fiberglass insulation in and stuff it in the pipe leaving it right at the opening where the diffuser goes.
Put the diffuser back on and your magnetic sign piece and you have an insulated, sealed area that is easy to undo. And of course it is cheap to do this and can be used over and over. I have used this many times as a temporary block during remodeling. DanT