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  1. #1
    Join Date
    May 2011
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    7

    Default Heating/Cooling Return Air Question

    Hey all,

    We just bought a relatively small home, 1400 sq ft here in Boston. The first floor is 1/2 below ground level and is always quite cool, and the second floor is always warm, even when it's in the 50s outside. The HVAC system was installed new less than a year ago and heats the first floor quite well. To keep the second floor from getting even hotter i've closed all the vents on the second floor. My question is regarding return air. The system only has one air return vent, that being on the second floor. Does it matter that there is no return on the first floor, and would putting one in make a difference to stabilize the temperature between the floors? I could fairly easily install a return air vent on the ceiling of the first floor and am wondering if there would be any benefit to doing so? Ideas?

    Thanks in advance!

  2. #2
    Join Date
    Jul 2009
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    Northeast
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    661

    Default Re: Heating/Cooling Return Air Question

    Another return on the first floor wouldn't hurt, it should be within 5 feet of the stat and large enough to bring back to the furnace the amount being supplied. How big is the return on the second floor? Most systems aren't balanced after there in stalled so closing a few supplies down some and opening some up may help. Since you closed the second floor supplies down have you noticed any difference.

  3. #3
    Join Date
    May 2011
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    7

    Default Re: Heating/Cooling Return Air Question

    Quote Originally Posted by Sten View Post
    Another return on the first floor wouldn't hurt, it should be within 5 feet of the stat and large enough to bring back to the furnace the amount being supplied. How big is the return on the second floor? Most systems aren't balanced after there in stalled so closing a few supplies down some and opening some up may help. Since you closed the second floor supplies down have you noticed any difference.
    Thanks for the quick reply. You mention a "stat" above, but I'm not sure what that is... As for the return on the second floor, it's on the floor of a hallway and the inside grate measures 5.5"x13.5". I have closed all the top floor supplies and downstairs warms up nicely, however I'd certainly like to be able to leave all the supplies open/partially open and heat or cool both floors evenly if that's possible.

  4. #4
    Join Date
    Jul 2009
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    Northeast
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    661

    Default Re: Heating/Cooling Return Air Question

    If that's your only return then it's way to small, I figure it's only good for 500-600 CFMS and even though that may be good for the second floor, (depending on the size of the second floor) you should be pulling back an amount in the area of 1500 CFMs total for the house or at least the amount being supplied. Go to your furnace and measure the supply duct that's coming from the furnace, if there is two then measure both. Then look for another return on the first floor and get back to us. A stat is just short for thermostat, the reason it should be so close is because you want it to measure the temp of the return air. As the room gets warmer (heat) or cooler (A/C) the temp differential reduces or gets closer until the stat satisfies. Send me a private message.

  5. #5
    Join Date
    May 2011
    Posts
    7

    Default Re: Heating/Cooling Return Air Question

    Quote Originally Posted by Sten View Post
    If that's your only return then it's way to small, I figure it's only good for 500-600 CFMS and even though that may be good for the second floor, (depending on the size of the second floor) you should be pulling back an amount in the area of 1500 CFMs total for the house or at least the amount being supplied. Go to your furnace and measure the supply duct that's coming from the furnace, if there is two then measure both. Then look for another return on the first floor and get back to us. A stat is just short for thermostat, the reason it should be so close is because you want it to measure the temp of the return air. As the room gets warmer (heat) or cooler (A/C) the temp differential reduces or gets closer until the stat satisfies. Send me a private message.
    Tried to send you a PM but my total post count is too low and it is disabled until I hit 15 posts on this forum. Here's what I wrote:

    So our first floor, the "cold" floor is about 650 sq ft, and the second floor, the "warm" floor, is about 800 sq ft. I verified that the second floor is the only floor with a return, though there are exhaust vents in every single room. I took some pictures of the heating unit in case you are interested. The return duct (on the right side of the photos) measures 20" x 8.5", and the exhaust duct going back to all the rooms on the first and second floor measures 20" x 18". Since the return on the second floor is directly above the ceiling of our guestroom downstairs, my idea was to bust through that ceiling of the first floor and install another return that way. Pretty novice I know, but it would allow air to return to the unit from the first floor. Only obvious issue is that the actual duct in the floor is probably too small as well...

    Pictures link: OK SO I CANT POST LINKS EITHER UNTIL MY POST COUNT HITS 10, FRUSTRATING!

    Thank you in advance for any help.

    Regards,

    Forrest in Boston

  6. #6
    Join Date
    Aug 2007
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    The Great White North
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    4,045

    Default Re: Heating/Cooling Return Air Question

    Unfortunately you have a less than desirable setup with only one return to begin with and located on the second level and doesn't sound like it's sized properly. In reality there should be a return in every room that have supplies run ( excluding bath rooms )

    Adding a return(s) definately sounds like what's needed in the lower level to balance the static pressure. Putting the return in the ceiling isn't the ideal location since it will draw out the warm air -- that naturally rises -- out of the room. It also depends where the supplies are located -- if they are also up high then having the return high will create a short circuit of air flow not allowing much warmth getting down to floor level. If the return(s) can be located down toward floor level would be benificial.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  7. #7
    Join Date
    May 2011
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    7

    Default Re: Heating/Cooling Return Air Question

    Quote Originally Posted by canuk View Post
    Unfortunately you have a less than desirable setup with only one return to begin with and located on the second level and doesn't sound like it's sized properly. In reality there should be a return in every room that have supplies run ( excluding bath rooms )

    Adding a return(s) definately sounds like what's needed in the lower level to balance the static pressure. Putting the return in the ceiling isn't the ideal location since it will draw out the warm air -- that naturally rises -- out of the room. It also depends where the supplies are located -- if they are also up high then having the return high will create a short circuit of air flow not allowing much warmth getting down to floor level. If the return(s) can be located down toward floor level would be benificial.
    Well crud, putting the return in the ceiling is just about as far as I would go with this project; putting it anywhere else i'm going to leave to a professional. Sounds like they are going to have to start tearing up walls to fix this thing, sad given it's a brand new install.

  8. #8
    Join Date
    Jul 2009
    Location
    Northeast
    Posts
    661

    Default Re: Heating/Cooling Return Air Question

    Did you have the system installed or buy the house after it was put in?? Either way I'd try to get the original installer to fix it or call someone, I live in East Bridgewater, 508-456-1161. I don't know if I can give out my number on the forum but we'll find out.

  9. #9
    Join Date
    May 2011
    Posts
    251

    Default Re: Heating/Cooling Return Air Question

    what size in the system installed. At 1400sq feet in Boston, I'm think that since it's half belwo ground it will have descent insulation, so a 2 - 2-1/2 ton A/C and a even jsut a 60k BTU furnace is probably adequate.

    I'll be it has a 80kBTU furnace and a 3 Ton A/C.


    I'd start by trying to increase the size of hte upstairs return and then add an additonal return on the 1st floor near the thermostat.

    DO NOT CLOSE OFF VENTS! You can kill you furnace and expecially the A/C unit. Better to add more vents to the 1st floor if needed.

    The upstairs isn't overheated, so much as the downstair is underheated comparatively. Add a couple more supplies to the first floor if possible, and then close a damper located near hte furnace in the summer so you don't overcool the 1st floor. Just like tunring off hte humidifier in winter, you'll have a "summer/winter" setting for the suplly branch to the 1st floor.


    Another note on oversize HVAC systems. Oversized units run less time total. Therefore temperature imbalances are made much much worse. For example, if the upstairs is hot in the summer, one might think they need to unsize the HVAC system. that would infact make the problem even worse.


    Another thing to consider is relocatign the thermostst to the 2nd floor... or consider installing a zone system so you have 2 thermostats.

  10. #10
    Join Date
    Jul 2009
    Location
    Northeast
    Posts
    661

    Default Re: Heating/Cooling Return Air Question

    It sounds like your return is the right size for the upstairs, does the 20x8 go all the way up or do you have a smaller return run coming from the Main return? If the 20 x 8 goes all the way up you need a bigger return grill. The 20 x 8 is good for 800-900 CFMs but you'll only get that after you enlarge the return grill because you can only fit so much air through that opening. You have to make up about 600 CFM's and tying into your existing return won't help, you can only move so much air at a time. You have to start at the return plenum, that's where your additional return has to come from. It's not hard if you know what your doing and in order to get everything running right everything has to be right to begin with. You have to have at least as much return air as supply, you can have all the supplies you want but if your return is to small where will the air come from? Good Luck

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