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Thread: Cold Air Return

  1. #1
    Join Date
    Apr 2008
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    Default Cold Air Return

    I have a pre-fab home with a forced air furnace in the basement and one cold air return in the dining room. A previous owner finished the basement and added a cold air return in the basement (about half the size of the upstairs one).

    I notice that most of the cold air from upstairs simply flows down the stairs (which are only 10 ft away from the cold air duct). As a result my basement is usually cold.

    Would there be anything wrong with simply closing the upstairs return and putting a grate directly on the furnace intake downstairs? Thus drawing all of my cold air out of the basement? It seems to me that this would do a much better job of circulating the heat.

  2. #2
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    Default Re: Cold Air Return

    The cold air return on the main level is the only one up there ?
    If this is the case I'd be suspicious the heating system isn't balanced very well.

    Ideally there should be a return air vent in each room of the house .... with the exception of bathrooms and kitchens .... these would be serviced indirectly from nearby return vents .... one reason the bathroom doors have a larger gap between the bottom of the door and floor.

    The cold air return serves a very critical role in the balance of air circulation. Without the proper amount of return air to the furnace this would create a pressure imbalance. Think of using a bicycle pump .... when blowing up a tire that's flat. Initially it's fairly easy to pump air but as the tire becomes more inflated the pump becomes harder to use .... because of restriction from the air inside the tire causing back pressure .

    A similar thing happens with the furnace ......in other words the amount of air being provided from the heat vents needs to have an amount of roughly equal to that being removed from the room to not create a back pressure. If that happens the furnace needs to draw air from somewhere or it will simply not supply air into rooms that are too full .... putting a strain on and damage the furnace blower.

    In my opinion the cold air return in the basement is really not the source of the problem.
    Having a cold air return in the basement can be beneficial for increasing the performance of heat circulation for this space ....... it would not be a good idea to rely on this location for the entire house.


    Hope this helps.

  3. #3
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    Default Re: Cold Air Return

    I kid you not. I have followed the ductwork and double checked everywhere. There is only one cold return on each level.

    I do have an inbalanced system. It just seems to me that, short of running new ducts into every major room, I can improve the balance by increasing the amount of cold duct in the basement while simultaneously decreasing the duct in the upstairs. Not ideal. But would I be violating some serious rules?

  4. #4
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    Default Re: Cold Air Return

    I can improve the balance by increasing the amount of cold duct in the basement while simultaneously decreasing the duct in the upstairs. Not ideal.
    I'm not following what you mean by decreasing the duct upstairs.

    To be honest .... this is one of those situations that is not for a DIYer ... you should have an HVAC contractor evaluate your situation.


    Just a thought.

  5. #5

    Default Re: Cold Air Return

    I have no idea how this thing works. I have a similar question and this is the only thing place I can figure out how to enter it in this system. I have a house that is one and one-half stories. There is an air intake duct on the first floor in the ceiling and one at the top of the stairs at floor level [upstairs has two bedrooms and a bath; downstairs has master br plus kit, liv, dining, one and one-half baths]. About seven mths ago the in-ground ductwork was sealed off and and new ducts were installed in the attic [the upstairs ductwork was already in the attic]. A new air handler and heater was installed in the attic. My problem is that the upstairs air is at least 10 or 15 degrees hotter than the downstairs. Also, the upstairs air return duct seems to blow out air although I can see that it takes in air. That duct is tapped into the air return duct from downstairs and is somewhat smaller in diameter. Also, it has to travel a little upward and then downward to where it connects to the larger duct. Are there basic do's and don'ts about this sort of thing? I need to know what to insist on in ref to the work that was done.

    If there are instructions for dummies on how to use this web site pls let me know.

    Thanks.
    Julia

  6. #6
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    Default Re: Cold Air Return

    julia... having warmer temps. on the second level is not unusual since warm air rises ... also if the insulation isn't at a high value would also contribute to this.

    However ... because of this .... it's important to have a well balanced heating/cooling air delivery system.

    It sounds like the system you have isn't quite balanced properly ... though it's difficult to see over the internet.

    Things like improperly sized or poorly located ducting would certainly cause a lot of these kinds of issues. Also poorly fitted ducting ( leaky ) would certainly cause
    issues.

    It may be in your best interest to have a company do a balance test of your system. Basically they would measure the air flow from the supply vents and determine if the return vents are appropriate.


    Just a thought.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  7. #7
    Join Date
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    Default Re: Cold Air Return

    As has already been indicated, the cold air return on a forced air system is just as important and critical as the supply. The one return up and one return down is simply a 'cost-cutting' way to provide cold air return. There ideally should be a corresponding cold air return for every supply with the exception of bathrooms and kitchens.

    In other words, there should be a cold air return in each bedroom, living room, family room, dining room, etc. (with noted exceptions).

    The size of the cold air returns will depend on the size of the supply (hopefully correct) feeding the respective space.

    A professional should be able to spend a reasonably short amount of time, go through your home and provide you with their observations and recommendations. (much better than from us, sight unseen).

    As far as the cold air return from the basement, I would suggest that this be capable of being closed off. If the return is low, you could leave it open year round and it will pull the heat down off the ceiling and pull the cold air off the floor. Otherwise, if it is a high return, you would probably want to close it in the winter time so as to not 'assist' in keeping all the heat at the ceiling, resulting in a colder floor that is necesasry.

    By having the cold air return from the basement you also benefit from drawing this cooler air into the system to help offset the cooling requirements, i.e. this is where you cooler air is going to collect anyway.

    You may want to damper down the supplies that are feeding the basement in the summer time to allow that air to be routed elsewhere (perhaps 2nd floor). If the system was not altered (increase in capacity, etc.) then doing this should not adversely affect the system.

    I am a very strong believer in utilizing what is already in place if you can do so in a proper and effective manner. None of us in the industry can make warm air fall and cold air rise. (When I get that one figured out I will have baggy shorts and a metal detector on a desert island somewhere.)

    Anyway, it sounds like a very 'cost-conscientious' return system was installed originally, and I would suggest having an HVAC professional come out and go through the entire system and based on the results of that survey, make the appropriate recommendations. Whatever they tell you should not deviate much from what I have indicated above.

    All the best, Irishmist.
    Live your life as an EXCLAMATION; not an explanation!

  8. #8
    Join Date
    Nov 2008
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    4

    Default Re: Cold Air Return

    I don't have a whole lot of time since I'm drywalling the unfinished basement this weekend, so any advice asap would be huge in this instance.

    I'd sure like some ideas on how to add cold air intakes to the two bedrooms downstairs? As well is if they are really that neccessary for the heating to be acceptable?

    The house is very open bi-level layout 1100 sq.ft up and down. There are multiple cold-air intakes upstairs. One larger / main intake at the base of the stairs in very open concept on the basement level as well. The building inspector made a deal out of it when he was there, and i decided to call him on it, saying "I wasn't under the impression it was building code to have these in the bedrooms" Well it's not code but highly recommended apparently so he said he wouldn't even right it down on the memo.

    In all fairness I won't be able to get these cold air intakes down to the base of the floor. They would have to be vented from the ceiling, and something is telling me this will take away from the heat that is captured at the ceiling level in the basement. Is this accurate assumtion or would i simply be better off to install cold air intake ceiling vents in both bedrooms in the basement? (Keep in mind the hot air vents are coming out of the ceiling as well in the basement). I realize the basement floor will be cold, but all basements are.

    Thanks for your help.

  9. #9
    Join Date
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    Default Re: Cold Air Return

    Hot air heating systems function best if there is at least one cold air return in each room ...... that allows the warm air to circulate better.

    The basement is no exception to the rule. What is different in the basement is that most of the ductwork is on the ceiling. If you leave a cold air return opening on the ceiling, it will simply steal all the hot air from the ceiling and return it to the furnace, and the cold air on the floor will never move.

    Cut into the cold air return trunk that is on the ceiling and drop a duct down to the floor. By extending the cold air return to floor level does a lot of good as it will vacuum up the cold air off of the floor and send it back to the furnace. That in fact will draw the warm air down, and help warm up the floor.
    It's likely you wouldn't require anything larger than a 5 inch duct for each room.

    One caution is to have the cold air return openings equalling half as large as the sum of all the hot air outlets in the basement. That will assure that the basement does not come under negative pressure that could cause backdrafting with the chimney.


    Hope this helps.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  10. #10

    Default Re: Cold Air Return

    I'm finishing the basement and it's time to run additional heat runs and install cold air returns. I know that each room downstairs needs a cold air return. My question is, can I simply cut a hole into the exsisting cold air returns that already service the upstairs or do I need to connect directly to the main run? Would utilizing the exsisting main floor runs have any negative effect on the system?

    Thanks

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