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Thread: Return Air

  1. #14
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836

    Re: HI VELOCITY

    Originally posted by zoom38
    In the Unico install manual they only have one central return. Is this not the way to do it? Should there be a return in each room? Or is it that because it is hi velocity only one central return is necessary.
    High velocity or not,the supply air needs to get back to the return ,somehow.Under the door may be a path ,if not enough add a return,or transfer grille.

    If the supply air to a bedroom,can't get out and back thru the return to the fan,that room will become pressured ,causing "exfiltration",air being forced out of the house.

    The return is "looking" for that air,air in the fan equals air out,if it can't "find",it causes infiltration,pulling out side air in,in the part of the home with the return.

    Can be a major factor in high bills,and indoor air quality.

  2. #15
    Join Date
    Jul 2004
    Posts
    322
    My kids live mainly upstairs and my wife and I live down. Two separate systems. The upstairs has its own returns, which makes sense if the kids go off to college and I don't want to use the upstairs much. I can pretty much shut down the whole upstairs system.

    On the other hand, I've thought about adding a return upstairs to service the downstairs unit. The reason is that it's warmer upstairs and there are times when the heat comes on downstairs and it's almost warm enough for AC up. With the added return I could just run the fan and move some of that warm air downstairs in the winter. I assume it would also take some of the load off the poor little upstairs AC which runs constantly in the summer. So I can't decide what to do.

  3. #16
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
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    18,836
    Best to run the upstair at say 82° summer and 60° winter,prevent mold and freezing.


    May want to add that return,as it will catch some of that heat that is rising ,may not need to after the kids are gone.

  4. #17
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    Zoom38 said:

    >>In the Unico install manual they only have one central return. Is this not the way to do it?
    >>Should there be a return in each room? Or is it that because it is hi velocity only one central return is necessary.

    What I don't know about the Unico system is tons. So please let me ask *you* a relevant question about it. Does a Unico system deliver 350-400 CFM of air per ton of AC capacity like most standard systems do?

    My train of thought is... air dumped into any room is going to try to get back to the central return under the door or whatever way is easiest. If Unico delivers the same amount of air, it seems to me it has the same potential for pressure imbalances when doors are closed. If it delivers much less air, then pressure problems at least would be reduced. Just looking at the pressure side of things, I have little knowledge of how that would affect room-by-room temperatures.

    Regards -- P.Student

  5. #18
    Join Date
    Nov 2004
    Posts
    136

    Re: HI VELOCITY

    Originally posted by zoom38
    In the Unico install manual they only have one central return. Is this not the way to do it? Should there be a return in each room? Or is it that because it is hi velocity only one central return is necessary.

    Unico only needs one return to allow air to move across the evap coil, it relies on what is called aspiration to circulate the air in the space. It delivers about 40 CFM @ something like 2000FPM per supply nozzle and only requires 200 CFM per ton. It’s nothing like a conventional system.

  6. #19
    How about this. Could I just cut inot the return air duct for the upstairs unit and the main down stairs unit and put a standard duct between the two. and if I did this would the down stairs unit then begin to pull warm air from the upstairs and cycle it to the downstairs area? and visa versa in the summer.

    And would there be issues if both units were running?

    I guess I could put a in duct fan to push air in the direction I want it to go?

    One thing you need to realise I have a home automation system in my house that controls each thermostat and I have temp sensors in every room the Attic and outside so I can program the system to do the correct thing based on where the heat or cold is located and pump air in the direction that would make sense. I caould also have the system just run fan without turning on the heat pump unit if there is enough heat to pull from the upstairs?

    Before i do any of this I guess I need to know what makes the most sense as fare as duct work returns etc.

    Problem it is almost imposable to run additional duct work as I have a two story house and it is on a SLAB so there is no access to run anything except in the attic. But all the units are located in the attec.

    AB

  7. #20
    Join Date
    Jul 2004
    Location
    midwest
    Posts
    2,868
    Dash, I will agree that the 3M filters are the cause of a lot of problems but the fact that they load up to fast is not the real problem with them. Loading up fast means they are doing a better job than a cheap filter and the only way to get around this is more filter area. In the perfect world all homes would be better if they used the 3M filters and had enough filter area to use them. P Student even says this in his post and did't defend his statement about increasing filter area and then being able to use any filter you want.
    Quote
    Many older houses have duct design which is kind of neglectful, with resulting excessive vacuum in the return (and excessive External Static Pressure the equipment must work against). If that is your situation, and you can afford to spend a few hundred, you can correct both problems at once by adding return capacity and having it located in the bedrooms. Once you have done that, assuming you have generous return capacity and filter area, you will be free to use almost any filter you want without harming the equipment or airflow.

    100% correct, as long as you have enough filter area you can use these filters.

  8. #21
    Join Date
    Aug 2003
    Posts
    1,841
    Loading up fast means they are doing a better job than a cheap filter and the only way to get around this is more filter area.

    good point.

  9. #22
    When did 3M filters become the topic ?

  10. #23
    Join Date
    Aug 2003
    Posts
    1,841
    I answered your question they do that to save money if you tell them to add a return then they will,but they will make you pay more.

  11. #24
    They did not offer me that as an option.. I did not know enough to ask. but problems with my professional install has resulted in me looking for information to help me find out more about the subject.

    This board has offerd much help and frustration..

    I would have spent what ever it took to do it right But I was led to beleve that I was getting the best solution that could be got.

    Now the house is built and there is no way to go back and add or change things as it is a two story house and it is on a Slab..

    I dont want to have them start cutting into walls and SR to add stuff.

    And it would cost much much more to do now than when it waas under construction.

    In future I will not trust the HVAC pro just because he has a license. I will educate myself and become a DIY-er as I am now convinced that this is the only way to get it done correctly.

    IT is not about the money if the solution works. And now after spending time looking at people post on this board I see the same lack of customer care as the local contractors have in my area.

    I guess it is an HVAC thing but it is also my money and I will look for someone that is truly intrested in solving my needs. for this I will pay wat ever it costs..

    AB

  12. #25
    Join Date
    Aug 2004
    Location
    middle georgia
    Posts
    239
    Andrew, I am a contractor here in middle GA. If you would like I could come by next week and see if we could find an inexpensive solution to your problem.
    Please step AWAY from the condensing unit.

  13. #26
    Join Date
    Jul 2004
    Location
    midwest
    Posts
    2,868
    Without looking at your house we can't tell you what would be ideal. Most houses with a common return will work fine and you would not notice much difference by adding more returns. If you add more returns they would have to be filter grills or if the units are easy to get to you could change it so the filter is in the return right before entering the unit. By connecting the two returns from the upstairs and downstairs units you could start pulling air back through the supplies of the unit thats not running. In new construction we always put returns in all rooms but the bathrooms and kitchens but it is easily done with the walls open.

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