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Thread: HVAC 2nd Floor reversed intake duct ?

  1. #1
    Reserach Scientisit LB's Avatar
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    Post HVAC 2nd Floor reversed intake duct ?

    Situation = Trane Heat Pump 5 ton HVAC system [1 zone] was installed with the 2nd floor duct work reversed---intake ducts located just below ceiling is 'sort of' blowing cool air & lower ducts are acting as intake --- results obtained by holding tissue infront of vents.

    Questions: Is there any possibility of damage to the system if this configuration has been in place for over 12 months? Would there be more load put on the system---more electicity used in a given period of time?

    PS - Thanks to all who submit and responsd - I have learned so much over the past 4 years redaing this and the other thread - Terry thanks!!!!!
    Linda

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    Retired Defense Industry Engineer jadnashua's Avatar
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    The most efficient way to cool is to dump air from above. The cold air is denser, and it will naturally fall down. If you tried to push it up, you'd end up with cold feet, and a hot head. Heating is the opposite, you want to put it in low, and take the hottest stuff out of the ceiling, but most people end up with the cold air return on the other side of the room down low, so it tries to go up, then falls back down after it's cooler out the other side of the room.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Reserach Scientisit LB's Avatar
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    Jim - thanks for the response! I am aware of the principle - the configuration of the openings and duct work were done prior to my taking ownership of the home.

    What I am concerned about and seeking general information on is the potential for issues down the road due to 'extra' work/load the HVAC may have been doing/under since the late 2008 install date. I am having the original contractor correct the 'duct reversal' and I want to make sure I address any other issues now - rather than later. Thanks!
    Linda

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    In the trades Dana's Avatar
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    The HVAC system can't be damaged by "extra" work or load, unless it's set in such a way that it short-cycles (which it might do if the thermostat was located directly in front of a supply register.) If run times are typically on the order of 10 minutes or more, it's not a problem. If they're under 5 minutes and multiple times per hour you'll be running at lower efficiency, you're putting more wear on the system, and it's looking for ways to set up the controls to lengthen the cycles (either by adding hyseresis to the thermostats or setting a minimum run time.)

    Even if it's short-cycling it's unlikely to have worn anything out in only a couple of seasons, but short cycling for a cooling season or two can reduce a 25 year anticipated lifecycle to something like 24 (and if allowed to continue it'd be junk or need repairs in 12-15 years.)

    It's unlikely that swapping which is the supply and which is the return will dramically affect short-cycling unless the thermostat would be too close to the supply register. If it's not short-cycling, don't sweat it. It's the number of cycles rather than total accumulated run time that tends to wear HVAC equipment out. If it's had to "work harder" by running longer (which is unlikely IMHO), the effect on longevitiy is in the statisical noise.

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    For simplicity, ducts for the second floor are often run in the ceiling. And, they'll often run the first level in the floor. Mine was that way for 20-years. I added radiant heat and the hydro-air is only a backup if I need to raise the temp faster (say after having been away for awhile) than the radiant can respond. When I remodeled, I moved all of the first floor ducts high up the wall. A/c is much more comfortable now. In Delaware, I'm guessing your're using a/c more than heat, so having the ducts in the ceiling is a good thing. Not as efficient for heating, but lots of places, commercial and residential are run that way. It's not 'reversed'...I think they designed it that way, and for primarily a/c, it's more comfortable. One thing I found that helps (not necessarily the wallet, though) is I keep my fan on all the time. I have a variable speed air handler, so unless heating or cooling needs to move the air, it runs at its lowest speed. This helps keep the air from stratifying, lets the humifier work better in the winter, and runs the air through the filter more often so there's less dust and pollen. A variable speed fan is a great thing, and I'd not want to live in a place without one.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Reserach Scientisit LB's Avatar
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    Dana & Jim - Thanks for responding!

    The information provided is just what I needed. I have not experienced 'short cycling' [at least I do not think so], so the 'statistical noise' maybe all that has taken place - yeah! As for the duct work location - my system is based in the basement beneath the 1st floor and then up into the attic adjacent to the 2nd floor - so not directly in the ceiling just place high and low. The house was retrofitted with two AC systems in 2004 to replace the window AC units. Heat had been oil-fired hot h20 boiler which now serves as the backup system for the heat pump. The Trane HVAC system has a variable speed fan and I also run it on 'circulate' so I get the benefit from air filtration, etc. I will see what the contrcator wants to do next week. Again thanks for the info!!!
    Linda

  7. #7

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    Keep monitoring.......... I have the similar case

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