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  1. #1
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    Question Add a Cold Air Return?

    I have a two story home built in 2006, no basement. The furnace (gas-forced air) is on the second floor and the only cold air return is on the outside wall of the utility room where the furnace is (second floor). In the winter, the living room (main level) is very very cold and the upstairs (bedrooms and bathrooms) is warm. If we set the thermostat at 68 or above the furnace will run nonstop, heating the upstairs while downstairs remains cold. I only have three single vents in the ceiling to heat the main level. The question is, can I put a cold air return in the living room to help circulate the air and keep the warm air from being sucked up the stairs to the only cold air return? I can hit the existing cold air return box on the second floor by going through the ceiling in the living room. So, do I just add a grille to the living room ceiling and tie it into the return upstairs, or build a box/bump out from the living room wall with a grille at the bottom and tie that bump out into the return upstairs? And will either of these help the situation? Any help is greatly appreciated.

  2. #2
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    Default Re: Add a Cold Air Return?

    Quote Originally Posted by jbened02 View Post
    I have a two story home built in 2006, no basement. The furnace (gas-forced air) is on the second floor and the only cold air return is on the outside wall of the utility room where the furnace is (second floor). In the winter, the living room (main level) is very very cold and the upstairs (bedrooms and bathrooms) is warm. If we set the thermostat at 68 or above the furnace will run nonstop, heating the upstairs while downstairs remains cold. I only have three single vents in the ceiling to heat the main level. The question is, can I put a cold air return in the living room to help circulate the air and keep the warm air from being sucked up the stairs to the only cold air return? I can hit the existing cold air return box on the second floor by going through the ceiling in the living room. So, do I just add a grille to the living room ceiling and tie it into the return upstairs, or build a box/bump out from the living room wall with a grille at the bottom and tie that bump out into the return upstairs? And will either of these help the situation? Any help is greatly appreciated.
    Adding a return air grille in the living room will help, but it may not solve the problem. It's worth trying because it's cheap and easy to do. Extra return air never hurts any forced-air system.

    Is there a door at the top or bottom of the stairs that lead upstairs? If so, this makes the upstairs and downstairs two separate pressure zones, and would exacerbate the problem you're having, and in this case, adding a return from the lower floor is most certainly a good plan.

    If there's no door on the stairwell, then adding a return may not help very much, because you must remember that returns do not acually "suck" the air from spaces--a return is actually only a path for the relief of pressure that is created by the "push" of the supplies. So, in your case, opening up a return that also communicates with the upstairs supplies will also allow the upstairs supplies to push more easily. Of course, it will also allow the downstairs supplies to push more easily, but the proportion of airflow will remain much the same, with the same frustrating result: the upstairs will heat more quickly than the downstairs.

    An even easier way to deal with this problem is to set your thermostat to "fan on" rather then "fan auto", so that the blower runs even when the furnace is not firing. What this does is to continue to mix the air in the house, thereby averaging out the temperatures better throughout the house. Try it, at least as a first measure.

  3. #3
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    Default Re: Add a Cold Air Return?

    I agree with some of what was posted.
    Adding a retrun down on the lower level may help.
    I would suspect that the heat vents are on the ceilings if so then you would place the returns down toward the floor.
    This will draw the cooler air from the floor level and help with trying to circulate the heated air better.
    Otherwise, if the returns were also on the ceiling the warm air from the supplies would be sucked into the returns.

    Sounds like there should be an evaluation done by a HVAC company to properly balance out the system.


    you must remember that returns do not acually "suck" the air from spaces--a return is actually only a path for the relief of pressure that is created by the "push" of the supplies.
    That is the intended flow charcteristic in forced air systems.
    However , I'll disagree in that the return does indeed "suck " ( draw in ) air in.
    That's the configuration of a blower -- inlet sucks ( draws ) in air --- outlet exhausts or pushes air.

    In a case of a return that's larger than the supply will actually create a negative pressure because it draws more air out than is being supplied ---- unbalanced.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  4. #4
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    Default Re: Add a Cold Air Return?

    There is not a door at the top or bottom of the stairs, which is part of the problem - all the warm air from downstairs gets sucked right off the ceiling where the vents are and up the stairs to the return. So, it sounds like if I do add a return I should go the route of building a bump out from the living room wall and put the grille at the bottom. I'll try switching the fan for now and welcome anymore thoughts on the issue.

  5. #5
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    Default Re: Add a Cold Air Return?

    .....and do I add a return at the bottom AND top of the bump out in order to open/close the appropriate one for A/C vs. heat?

  6. #6
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    Default Re: Add a Cold Air Return?

    Quote Originally Posted by jbened02 View Post
    - all the warm air from downstairs gets sucked right off the ceiling where the vents are and up the stairs to the return.
    To fix this problem, it's important to understand some basics of how a forced-air system is supposed to work.

    Having both the supplies and the return(s) in the ceiling is not necessarily a problem if the supplies have adequate throw and velocity. If the supplies are lacking these things, the re-location of returns will not fix the problem, but the size of the return could.

    If you doubt this, look up at the duct system of any Wal-mart or other big-box store: you will see supply ducts and registers branching out all across the ceiling, but you will see only one return, and it will be located in the ceiling right under the rooftop unit.

    Why does the air not simply get sucked from the ceiling into the return, or, in other words, simply short-circuit without actually heating or cooling the store? Because returns do not suck air; they are no exception to the law of physics which states that air, water and other fluids always flow from an area of greater pressure to an area of lower pressure. The supplies drive the performance of any forced-air system, not the returns. Returns are simply a path for pressure relief.

    If your system had been designed and installed properly, the supplies at the ceiling of the lower floor would easily heat and cool that area even with the one central return on the upper level.

    What to do now? Increasing the size of the return air path will help, because an undersized return increases the resistance that the furnace blower must overcome to move the air. If you can reduce that resistance on the return side, the supply side airflow (both velocity and volume) will increase, and you will notice improved performance in terms of better throw and mixing from the supply registers.

    Running the blower on low speed constantly will also help mix the air better, thereby averaging out the temperatures of upper and lower floors.

  7. #7
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    Default Re: Add a Cold Air Return?

    Quote Originally Posted by canuk View Post
    In a case of a return that's larger than the supply will actually create a negative pressure because it draws more air out than is being supplied ---- unbalanced.
    That is true only in cases where there is more than one space being conditioned.

    If all the supplies and the return are in one space, or spaces that freely communicate with each other, the supply and return flows will always be equal.

  8. #8
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    Default Re: Add a Cold Air Return?

    Sorry but I have to agree with Canuck on this, a return most certainly sucks the cold air, if designed right or warm air if designed wrong. rdesigns keeps on saying that returns are only a path for pressure relief, that could not be more wrong. You have to have a return in order to get the cold air out of the room during heat season and the warm air out during cooling season. In a perfect world you should have a return in each room, especially if there are doors that are kept closed. Unfortunately some homes use a central return that may bring back as much air as is being supplied but will leave cold spots in areas in a home. Your return should also be in the floor for heating as warm air rises or in the ceiling for A/C to rid the room of the warm air. Even though I don't know the layout of your house it doesn't sound like your heat system was designed correctly but, there may have been extenuating circumstances.
    AS for Walmart or Big Box, Lowes or Home Depot, your talking Commercial vrs Residential, or one big room vrs. a 6, 7, or 8 room home. You can't take the Heat Design of one and compare it to the other.
    Like I said, it sounds like a poor design and adding another return will most certainly help. Other things to consider are stat location. I would add at least couple returns to the first floor (if possible) and move the stat to the room most occupied and near a return, (living room)? Good Luck!!!
    Last edited by Sten; 02-03-2010 at 01:25 PM. Reason: More info

  9. #9
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    Default Re: Add a Cold Air Return?

    Quote Originally Posted by Sten View Post
    AS for Walmart or Big Box, Lowes or Home Depot, your talking Commercial vrs Residential, or one big room vrs. a 6, 7, or 8 room home. You can't take the Heat Design of one and compare it to the other.
    Air behaves in a consistent manner, regardless of how many spaces are involved.

    Canuk and Sten have both no doubt experienced cases where adding a floor return helped with cooling, and adding a ceiling return helped with heating.

    Taking heating as the example, the explanation for why it helps is two-fold: an enlarged return will reduce the resistance on the system's return side, thereby giving more "oomph" to the supplies; and, because warm air rises, the air that gets pushed into the ceiling return will be warmer ("stratification").

    However, if the supplies were behaving porperly, stratification would not happen--this is why Wal-mart systems work. The system is designed so that the supply registers throw the air in a pattern that adequately mixes the air.

    House systems should be designed to perform the same way--no matter how many rooms there are, each should have supply registers that throw and mix the room air properly, and each room should have an unrestricted path (duct, tranfer grille, jumper duct, etc.) that allows for pressure relief.

    Air cannot be pulled, it can only be pushed. When you "suck" in a breath of air, what is actually happening is that atmospheric pressure is pushing air into an area of lower pressure--your lungs. This is true of duct systems as well.

    I stated air can't be pulled--there is one exception that can confuse people, and that is gravity. Gravity can pull air, so that's why cold air sinks and warm air rises. And that is why ceiling returns can help an under-performing heating system that is not adequately mixing the air to prevent stratification.

  10. #10
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    Default Re: Add a Cold Air Return?

    First off you have it backward, read my post, return on floor for heating, ceiling for A/C. As usual we can beat this topic to death, but you have a blower motor that's pushing air through the supply plenum and is pulling it through the return, but you say it's gravity bringing back the return air. *** thanks for the schooling.

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