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  1. #1
    Join Date
    Aug 2008
    Location
    DFW - Texas
    Posts
    21

    Return intake placement problem?

    My situation: I have a 1 & ½ story house (2,478 sf) with an entry and a living room that have 20’ ceilings. The second floor has half walls that look down into the living room. I think my two units are 4 ton (dn) and 2.5 ton (up). There are only two return air vents/intakes in the entire house – one for each unit – and they are both mounted in the ceiling of the upstairs hallway. Brand new coils in the big unit (old ones were leaking) and a brand new compressor in the big unit (old one died last year). Outside coils/fins are as clean.

    The living room with the high ceiling faces south & west, with the west wall having a ton of windows. (By now you’re probably getting the idea this house was poorly designed?... Me too.)

    Even with the thermostat set at 78, our units are running literally all day long, without a break. Granted, it’s Africa-hot here in Dallas right now, but my units couldn’t keep the house any cooler than about 82 yesterday.

    My thoughts…
    - We have one high arched window that is uncovered on that west wall – that’s a no-brainer that I should’ve taken care of long ago.
    - Attic radiant barrier… Thinking that maybe I should study the cost & DIY possibilities of buying the rolled stuff and covering the underside of the attic.
    - But, my main concern is my return air vent situation. It seems to me that this design of having both of the intakes mounted in the upstairs ceiling is a bad one. Wouldn’t the big unit be able to operate more efficiently if it were able to pull air in from the downstairs area (say, an 8’ ceiling in my dining room, for instance) ?

    Any feedback or advice anyone can offer will be most appreciated.

    Thanks,
    Luke

  2. #2
    Join Date
    Mar 2005
    Location
    Houston, Texas
    Posts
    11,871
    How would you run the duct? It's hard to say a lot, not being there.

  3. #3
    Join Date
    Aug 2008
    Location
    DFW - Texas
    Posts
    21
    I've thought about that a bit... Right next to the intakes, theres a 2nd floor wall section - sort of triangular in shape... picture a coke can, but like a triangle instead of a cylinder. I think this space is hollow. It's easy enough to get to in the attic, very near the existing duct. And, it's directly above the dining room downstairs with its 8' ceiling.

  4. #4
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,985
    Quote Originally Posted by lkrav View Post
    My situation: I have a 1½ story house (2,478 sf) with an entry and a living room that have 20’ ceilings. The second floor has half walls that look down into the living room. I think my two units are 4 ton (dn) and 2.5 ton (up). There are only two return air vents/intakes in the entire house – one for each unit – and they are both mounted in the ceiling of the upstairs hallway. Brand new coils in the big unit (old ones were leaking) and a brand new compressor in the big unit (old one died last year). Outside coils/fins are as clean.
    Check the blower wheel blades for lint, if loaded, the evaporator may need cleaning.

    The living room with the high ceiling faces south & west, with the west wall having a ton of windows. (By now you’re probably getting the idea this house was poorly designed?... Me too.)

    Even with the thermostat set at 78, our units are running literally all day long, without a break. Granted, it’s Africa-hot here in Dallas right now, but my units couldn’t keep the house any cooler than about 82 yesterday.

    My thoughts…
    - We have one high arched window that is uncovered on that west wall – that’s a no-brainer that I should’ve taken care of long ago.
    - Attic radiant barrier… Thinking that maybe I should study the cost & DIY possibilities of buying the rolled stuff and covering the underside of the attic.
    Some also use the new foam insulation under the roof & in other areas with good results. There window screen barriers, etc., & other procedures you could inquire about.

    - But, my main concern is my return air vent situation. It seems to me that this design of having both of the intakes mounted in the upstairs ceiling is a bad one. Wouldn’t the big unit be able to operate more efficiently if it were able to pull air in from the downstairs area (say, an 8’ ceiling in my dining room, for instance) ?

    Any feedback or advice anyone can offer will be most appreciated.

    Thanks, Luke
    On ceilings higher than 8' & attic or roof above, keep the Returns lower & leave the warm air as a barrier to slow heat transfer from the attic. The temperature difference determines the rate of heat transfer.

    Even with 8' ceilings if attic is not well insulated against heat conduction to ceilings, I wouldn't put Returns near the ceiling.

    I agree with you, & would put all of the Returns in areas with 8' ceilings!
    It is more cost effective, if at all possible, to condition a lesser volume of air.

    In the winter, the heat will also go to those 20' ceiling areas, so the high ceiling area is costing you more summer & winter.

    In my opinion, the duct system should be laid out to allow stratification so that the hottest air stays near the ceiling & is NOT mixed with the conditioned air.

    You will have to look at how those Supply registers or diffusers are located & their throw directions, etc.

    Also, lower airflows might work better, say 350-CFM per ton of cooling.
    How old & what SEER are your air conditioners?
    - udarrell

  5. #5
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    "Even with the thermostat set at 78, our units are running literally all day long, without a break. Granted, it’s Africa-hot here in Dallas right now, but my units couldn’t keep the house any cooler than about 82 yesterday."

    I'd say your system aren't working properly.

    Did they do better in the past summers???

    Return placenet that you have could work well if the supplies are properly sized and located.same for the stats,and all rooms have a return path the the ducted returns.

  6. #6
    Join Date
    Aug 2008
    Location
    DFW - Texas
    Posts
    21
    My units are almost 7 years old. Tract home that was built in fall of 2001. Units are York brand - I think 12 seer, but not sure as I'm not at home right now. Last Sept. the compressor on the 4T gave out and was replaced. A month ago, a leaking set of coils on that same unit (inside the attic portion) was replaced.

    The sytem has always struggled with the most extreme times of the summer, but it does seem to be worse this year. Of course, our temperature was over 105 yesterday, too, and this summer (overall) is worse than last.

  7. #7
    Join Date
    Aug 2008
    Location
    DFW - Texas
    Posts
    21
    <<<Return placenet that you have could work well if the supplies are properly sized and located.same for the stats,and all rooms have a return path the the ducted returns. >>>

    Dash - not sure I followed you about the "return path the ducted returns..." Every room does have a delivery vent, yes, but none of the rooms have intake vents. Each unit in the attic has one big intake duct, and they pull through a filtered grates (20" x 20" x 1") mounted in the ceiling of the hallway upstairs.

  8. #8
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    Hello Luke,

    I just returned from a 10-day visit to Dallas and boy was it hot this summer! Believe it or not I really felt the Houston weather was quite a relief.

    Radiant barrier is a great idea if your attic layout permits practical access for putting up foil. I did my own house as a long project, buying several times from this vendor local to you:
    http://www.energyefficientsolutions.com/

    I found the owner really likeable and suggest you give him a call to just talk about things. If your attic has a simple roofline it could be a decent project for a non-pro, I turned a new electric stapler into a very used one in the process. You likely will find the heavier grades of foil to be a luxury to work with. The light foil works just as well when up, but I found the heavier texture to be a convenience in the process.

    I would place the highest respect on what Dash tells you, plus a couple other board pros as well. I would always defer to his opinion, but if you would tell what size your AC units are he could better advise you whether that return size is big enough. A too-small return could restrict air flow (as could some other things) and make your typical Texas oversized ACs, perform like smaller units. My 3.0 and 3.5 ton units came with 20" x 30" return grilles and that was adequate but not generous. In my case I solved a problem by adding additional returns, in bedrooms and also in a ceiling.

    Also I must urge you as a fellow Texas homeowner, to look closely and carefully for any duct leakage in the attic. That will surely rob you of cooling capacity, in my experience lots of local HVAC pros don't talk about it much but any leaks are very much worth fixing. Dash's company offers testing and a sealing process which is not cheap but I would probably pony up the money if he were local to me.

    Best of luck -- Pstu

  9. #9
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Quote Originally Posted by lkrav View Post
    <<<Return placenet that you have could work well if the supplies are properly sized and located.same for the stats,and all rooms have a return path the the ducted returns. >>>

    Dash - not sure I followed you about the "return path the ducted returns..." Every room does have a delivery vent, yes, but none of the rooms have intake vents. Each unit in the attic has one big intake duct, and they pull through a filtered grates (20" x 20" x 1") mounted in the ceiling of the hallway upstairs.
    Rooms other then baths and the kitchen need a return path,or ducted return.

    With doors closed supply air needs a low pressure escape from the room,if not suply air will pressurize the room,forces air out cracks,and the area with the return duct will depressurize,pulling air in thru cracks,etc.

    This air out ,air in,adds load to the system,plus limits suppl air to each room,with the door closed.

    Simply feel the supply air with the door open,and have somone close the door,if the supply drops,it's costing you money.

    Return paths can be under the door,often to small,thru the wall,ceiling jumper duct,from a bedroom to the hallway.


    20X20 is too smallfor 2.5 tons,but not bad ,if all other ducts are sized coorect,for it.

    Surely the 4 ton has two of them,0kay,but not great.If the filters are in the grilles,small size is worse.

    Fort Worth has an Aeroseal duct sealer.

    www.areoseal.com

  10. #10
    Join Date
    Aug 2008
    Location
    DFW - Texas
    Posts
    21
    Thanks Dash. We keep the doors open throughout the house - even at night.

    I'm almost positive that my upstairs unit is a 2.5T and it definitely has just the one 20"x20" filtered intake. If that's just almost enough for a 2.5T, then it sounds like my 4T is starving for air with just its one 20x20 intake. If there's another one ducted into that unit, then the framers or drywallers must have goofed and walled it off, because there's not one anywhere. (I guess it sounds crazy, but that makes me want to count everything coming out of/into that unit in the attic and see if that didn't really happen.)

    If I really do have a 4 ton with single 20x20 intake... it sounds like that is a definite problem?...

  11. #11
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Quote Originally Posted by lkrav View Post
    Thanks Dash. We keep the doors open throughout the house - even at night.

    I'm almost positive that my upstairs unit is a 2.5T and it definitely has just the one 20"x20" filtered intake. If that's just almost enough for a 2.5T, then it sounds like my 4T is starving for air with just its one 20x20 intake. If there's another one ducted into that unit, then the framers or drywallers must have goofed and walled it off, because there's not one anywhere. (I guess it sounds crazy, but that makes me want to count everything coming out of/into that unit in the attic and see if that didn't really happen.)

    If I really do have a 4 ton with single 20x20 intake... it sounds like that is a definite problem?...
    One 20X20 return grille on a 4 ton,would be an issue,unless all the other ducts were oversized,not likely.

    Isn't that return noisey??

  12. #12
    Join Date
    Aug 2008
    Location
    DFW - Texas
    Posts
    21
    Yes, I guess it is noisy. You can hear it from downstairs.

    You said: "One 20X20 return grille on a 4 ton,would be an issue,unless all the other ducts were oversized,not likely."

    I assume "the other ducts" you're talking about are the delivery ducts to the different rooms... and no, they are not oversized. A couple (living room & master bedroom) are slightly larger than the others (bathrooms, dining room, etc.) but none of them are as large as the return air duct.

  13. #13
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
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    18,836
    Quote Originally Posted by lkrav View Post
    Yes, I guess it is noisy. You can hear it from downstairs.

    You said: "One 20X20 return grille on a 4 ton,would be an issue,unless all the other ducts were oversized,not likely."

    I assume "the other ducts" you're talking about are the delivery ducts to the different rooms... and no, they are not oversized. A couple (living room & master bedroom) are slightly larger than the others (bathrooms, dining room, etc.) but none of them are as large as the return air duct.
    Really didn't think they would be ,just and example of how the 20X20,could maybe ,maybe be okay.

    Second return covered by drywall ,is more likely,so check closely.

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