Replies

1. 
   Rebeccah_ | Jul 12, 1999 12:39am | #1

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   Uh-oh, I think we're planning on using stud bays for air returns in my new house... are there ducts that will fit within typical walls between the studs, so I don't have to have chases all over my house?

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   andrew_d | Jul 12, 1999 10:31am | #2

   *Yes, we have them -- 3.25x14 I think? -- but their capacity is limited. Larger ducts are more efficient because they have a much lower surface area to volume ratio and, I would speculate, less % loss to leakage. Chases can be cleverly hidden though -- consider the "coffered ceiling" thread...Does anyone worry about the fire hazard aspect of stud bay "ducts"? I know there is plenty of concern about plenum fires in commercial buildings -- nothing like a nice mechanical draft to stoke an otherwise small fire.

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   Barry_Miller | Jul 13, 1999 02:23am | #3

   *I rented a house once in Tidewater Virginia, and the return air register (approximateley 18"x18") on the staircase wall had been sealed by a previous tenant with aluminum foil across the duct and beneath the cover. Seemed odd to me, so I removed the foil. Come winter, there was a horribly cold draft coming from the return vent. The house had a crawl space, so I got into it and discovered that the builders had used the floor joist bays as return ducts, but they had left a six inch gap at the house's rim joist. The furnace was sucking in cold, outside air, and the same air was drafting into the house through that staircase register. We had moved into the house in June, so this also explained why the air conditioner hadn't seemed to be very effective.

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   andrew_d | Jul 13, 1999 11:09am | #4

   *Lost a hamster into a floor grate when I was about 6 years old. We had no idea where it had gone until weeks later when there was this ... smell. My dear mother turned the heat up all the way and we went to stay at a hotel for a while. She didn't explain for years, and to a 6 y.o. a hamster dematerializing seems reasonable enough. I sometimes wonder if there's still this little itty bitty skeleton collapsed in those ducts.Anyway, another reason for hydronic heat I guess. Hard to imagine wanting heat these days, but it'll come soon enough.

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   arrowshooter_ | Jul 21, 1999 03:10pm | #5

   *As to return air systems in houses I have found that a single return air grille located centrally and sized large enough works just great and avoids the use of a huge system of return air ducts and RA grilles cut in all over the house.I try to locate the furnace centrally so I can have a single RA duct drop straight down to a RA plennum on the side of the furnace. Usually a closet can be found adjacent to a central hall so you can construct a RA box in the closet with the RA grille in the hall. The box needs to be constructed and lined with duct board with baffles so there in no line of sight path from the grill to the equipment. In my home I used a 18inch flexible duct and ran straight down to a duct board box on the furnace. It is important with this type system to run the blower continuosly during heating and cooling. I used a 30X24 filter grille for the RA, the system is very quite and since the doors to the rooms in the house stay open most of the time we have no problem with return air getting back to the furnace. In my opinion it is usless to put RA grilles in all the rooms and all over the place. You just need to run the blower all the time for a great heating system. Any thoughts on this.

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   Marco_Simmoni | Jul 22, 1999 05:44am | #6

   *Hi A-Shooter,What do you mean by baffles? Are they within the RA collector so that turbulence is created in the return air? What is the ratio of grill surface to house volume, or furnace size or fan size or...?Thanks

3. 
   arrowshooter_ | Jul 23, 1999 05:33am | #7

   *Hello Marco: For sizing of RA grilles you need to determine the air requirements for your equipment (CFM) Most grille manufacturers publish spec sheets showing the size grille needed for a given air quantity and noise level, A filter grille will need to be larger than a regular grille but when in doubt you should choose a larger grille to reduce noise level, also a commercial type grille will handle more air at a lower noise level than a residential type. As to the baffle this is a partition placed in the return air box in such a way as to cause the air to travel a little further and not have a line of sight path from the grille to the blower compartment. The baffle can be made of duct board and placed in any number of ways to accomplish this objective, use your imagination this realy works for a quieter system. My son had a heating system with the RA grille and duct connected directly to the side of the furnace so if you removed the grille you could see the blower motor, this was extremely noisey. I made a baffle from a piece of celotex ceiling tile so the air had to come through the grille and up and over the baffle to get to the fan after which they could even hear the TV in this military housing unit.

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   John_Rupert | Jul 23, 1999 05:37am | #8

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   I have told my heating/cooling contractor I don't want him to use joist/stud bays for cold air returns. He says I' being unresonable. Am I?