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Old 12-27-2013, 07:23 AM   #16
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I'm with beenthere. You're going to have to establish some type of a thermal break to keep the cold air that comes in from the brick and filling the cavity.Otherwise you have good old fashioned physics. Probably don't want to hear this, but you maybe better off picking a couple of wall bays and opening them up and putting in the proper duct work in and insulating them properly. or run the duct outside the wall and box them in.
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Old 12-27-2013, 08:08 AM   #17
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I'm with beenthere. You're going to have to establish some type of a thermal break to keep the cold air that comes in from the brick and filling the cavity.Otherwise you have good old fashioned physics. Probably don't want to hear this, but you maybe better off picking a couple of wall bays and opening them up and putting in the proper duct work in and insulating them properly. or run the duct outside the wall and box them in.
The company that installed the new furnace suggested using 1/2 inch of spray foam in there but it seems a rather tight squeeze to get full proper coverage. There are a total of 4 return vents upstairs. 2 of them are just like shown in the picture and the other 2 I can actually get full access to by removing a few screws and a duct box to expose the joist space and wall space. For the two that I cannot get full access to is there something that is prefabricated that I can buy at lowes or home depot to just insert in there?
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Old 12-27-2013, 08:20 AM   #18
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You can get a Flex Camera, to allow you to get a picture inside the cavity. Harbor Freight sells them, along with the other Big Box. You may need to get a flexible light, to shine into the cavity, so you can get a better image.

As for the return issue, I would move them into the inner area of the home. You can use Closet's to get from the first floor to the Second floor, then build a box around the Return and Supply ductwork to hide them.




Last edited by gregzoll; 12-27-2013 at 08:22 AM.
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Old 12-27-2013, 08:23 AM   #19
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you might be able to find something, even something used for new linings in a chimney. But your still going to have to create some type of thermal break other wise the cold is just going to seep through the brick even if it is sealed and chill the duct work Is there a separate return for each room? can you seal the ones off that you can't get to and use the others? not to mention insulating all the other open bays.
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Old 12-27-2013, 08:29 AM   #20
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they used to make a duct that was oblong and flat so it would fit between wall studs and be covered. Best option is I think is to go with my or Greg"s idea and then even if you don"t have the cash at this time seal the bays both bottom and top otherwise they all act as mini chimney's and create drafts.
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Old 12-27-2013, 08:49 AM   #21
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you might be able to find something, even something used for new linings in a chimney. But your still going to have to create some type of thermal break other wise the cold is just going to seep through the brick even if it is sealed and chill the duct work Is there a separate return for each room? can you seal the ones off that you can't get to and use the others? not to mention insulating all the other open bays.
I forgot about the return vent in the hallway (on an inside wall) so there is actually 5 return vents upstairs. The grill for the return in the hallway is 12'x8'. I think this would give me room to seal off at least one of them and still have good air flow to the furnace. The return in the basement is 12'x8' and on an inside wall as well. Is 2 12x8 returns enough for the furnace or will that cause problems?
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Old 12-27-2013, 09:16 AM   #22
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you sure these are all returns for the furnace and not some type of passive cooling system for the summer? cool are being drwawn up from the basement and out through the attic. I'd think it would be wise to get your heat guy in there and see . If there is a dedicated cold air return to the furnace, then why all the other ones??? Also open and closing doors can have a big effect if they are to close to the carpet or floor. If door is closed to a room with no return it can have a direct effect on heat in that room..in with hot, out with the cold.
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Old 12-27-2013, 09:44 AM   #23
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you sure these are all returns for the furnace and not some type of passive cooling system for the summer? cool are being drwawn up from the basement and out through the attic. I'd think it would be wise to get your heat guy in there and see . If there is a dedicated cold air return to the furnace, then why all the other ones??? Also open and closing doors can have a big effect if they are to close to the carpet or floor. If door is closed to a room with no return it can have a direct effect on heat in that room..in with hot, out with the cold.
I am absolutely sure these are connected to the furnace. There is a duct running from it to the furnace. This was verified by the hvac contractor when I had my new furnace installed. There is a piece of wood at the top preventing air flow any further up the wall. I took a pic to show the piece of wood at the top.

The 2 inside wall returns give me about 200 sq inches of grill surface. I thought I needed 500 sq inches for 1100 cfm. So are you saying the two returns are enough and I can just fill those other cavities with spray foam to close them off?
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Old 12-27-2013, 11:01 AM   #24
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IMHO, the air in the attic is not coming down in the walls regardless if is air sealed or not. The stack effect feeding an attic doesn't work like that; http://www.wag-aic.org/1999/WAG_99_baker.pdf

The heat from rooms is mixing with the convective loops in that 6" air space, Fig.4 and others; https://docs.google.com/viewer?a=v&q..._NGatSVo3wzmAQ

Foam all at 1-3/4" (R-10.5) thick except RA ones, in those foam bricks at 3/4" thick only (R-4.5) for an 83% reduction in heat loss and still able to use as air returns; http://www.google.com/url?sa=t&rct=j...,d.cGE&cad=rja

Block others off from basement/room above at floor line for fire-stop required per code; http://publicecodes.cyberregs.com/ic...002_par017.htm Hit "next section" for fire-block materials used. The drywall/P&L will help air seal from the cavities.

With suggested thickness of foam, cavity insulation is not required, though RA chases on an exterior wall are never a good idea (unless more room for foam and still have NFA for RA), #4- "flush our toilets" was a good one, lol; http://www.buildingscience.com/docum...ong-from-start

Photos 7-9; http://www.buildingscience.com/docum...39-five-things

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17,000 dryer fires a year, when did you last clean the inside of the dryer near motor or the exhaust ducting?
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Old 12-27-2013, 02:45 PM   #25
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Don't seal off any of the return vents. Your probably need more then you have. I'm basing that on the tradition of most homes not having enough return. Specially older homes.
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Old 12-27-2013, 06:39 PM   #26
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I agree, that is what I said. How much is normal return air, how big is the furnace, rooms, etc.? Seems like someone could figure that size over the net.... or is it one where you really need to be there, beenthere? If it was 6" deep and the SPF 3/4" deep would the 4" x 14" be wide enough, times two places? (It does appear to only be 4" wide at the framing....) I wouldn't restrict it beyond how much? I'm sure the OP could give you the info you need....

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Old 12-27-2013, 07:29 PM   #27
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A normal 2X4(3.5"X14") wall cavity used as a return chase is only good for a max of 140 CFM. If he has 5 returns like that. Then he has enough for 700 CFM. Which is ok for a 45,000 BTU output furnace, which would give a temp rise of 60°F.
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Old 12-27-2013, 08:02 PM   #28
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A normal 2X4(3.5"X14") wall cavity used as a return chase is only good for a max of 140 CFM. If he has 5 returns like that. Then he has enough for 700 CFM. Which is ok for a 45,000 BTU output furnace, which would give a temp rise of 60°F.
The return in the living room takes up 2 wall cavities. Would this count as 280 cfm or still just be 140. there is also a return in the basement. The furnace is 70,000 btu.
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Old 12-27-2013, 08:14 PM   #29
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It would account for as much as 280 CFM.

A 70,000 BTU input 80% efficient furnace needs 865 CFM to keep temp rise down to 60°F.

A 70,000 BTU input 90% efficient furnace needs 972 CFM to keep temp rise down to 60°F.
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Old 12-27-2013, 09:25 PM   #30
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It would account for as much as 280 CFM.

A 70,000 BTU input 80% efficient furnace needs 865 CFM to keep temp rise down to 60°F.

A 70,000 BTU input 90% efficient furnace needs 972 CFM to keep temp rise down to 60°F.
I will not be removing any returns then. I already spent 7,500 on the furnace and 3,800 on the air sealing and insulation so I am trying to do this for as little as possible. Would it cost less to move the returns to an inside wall or do the thinner amount of spray foam in the existing returns.
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