Upstairs heat/ac vent - no air

Discussion in 'HVAC Heating & Cooling' started by garyl53, Mar 20, 2007.

  1. garyl53

    garyl53 Engineer

    Messages:
    54
    Location:
    Colorado
    Hi,
    I have a heat/AC vent in an upstairs bedroom that has little or no air movement. It is, of course, in a south facing BR that gets uncomfortably hot in the summer (even with the AC on). In general all of the other upstairs BRs are comfortable. Are there suggested ways to investigate the cause other than ripping the carpet out and tearing up the floor?
    Thanks,
    Gary

    PS: I tried a vent fan to pull air out but it doesn't do much, leading me to believe it might be blocked.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,817
    Location:
    New England
    There could be a damper somewhere, restricting the airflow. The ducts could be very leaky and the air is pouring out into the floor joist area, or, it could just be the end of the run, not insulated, and not very effective. Is there much air movement, but it is just not the right temperature? or not air movement at all?

    Sometimes, the builders are very sloppy when attaching ductwork, especially with the flexible round stuff. I had one run that had fallen out of the supply duct because they didn't use the right adapter, cut it a little short so there was tension on it, and then used duct tape to attach it rather than a tie wrap, clamp, or the metal sealing tape. Now, finding the problem can be a pain. Maybe someone with a remote control camera?
  3. garyl53

    garyl53 Engineer

    Messages:
    54
    Location:
    Colorado
    Thanks,
    I think I will see if I can open up the floor in a few places when we replace the carpet. My guess is it is not connected since their is no air movement that I can detect.
    Thx
    Gary
  4. garyl53

    garyl53 Engineer

    Messages:
    54
    Location:
    Colorado
    Hi,
    I finally traced the duct back to the source in the basement. I couldn't find any blockages or disconnected pieces. I think it is just a very long run with several turns. I calculated the EDL and it is over 100 ft. I tried a cheepo duct fan from HD but it did little to move air. I could feel some air for the first time. I ordered a Panasonic Whisper inline fan and plan on installing it in the basement at the start of the run. I installed a wall switch up in the bedroom to turn it on when needed on hot days. I'll let you all know how I make out with it next week.
    Thanks,
    Gary
  5. SteveW

    SteveW DIY Senior Member

    Messages:
    1,052
    Location:
    Omaha, NE
    I have the same situation - 2nd floor bedroom at the end of a run, with the blower in the basement. A contractor told me that this is a common problem - there is just not enough power in the average home furnace/AC setup to push cold air up two stories and then down the horizontal run.

    Their solution was to install a very expensive zone system.

    I have toyed around with the dampers and have been able to get more air coming out of the register, but still not optimal.

    Seems to me there should be a relatively simple solution - more powerful blower, etc.
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,817
    Location:
    New England
    take a close look at the manual for your furnace, there may be alternate blower speeds. It is not uncommon to need a higher fan speed in the summer for a/c than in the winter for heat. On the Trane air handler I have, there are some DIP switches on the controller that can vary the max fan speed over quite a range.

    The one thing that helped make my place much more consistent temperature-wise 1st-2nd floor was redoing the return ducts. That's somewhat extreme, but it worked. My feeling was that since heat always rises, I'd put my return at the highest point, winter or summer. In the summer, it pulls the hotest air out, and cools it. In the winter, it pulls that overheated air up there and recirculates it to the rest of the house. My place went from a 5-degree differential 1st to second floor, to about a 1-degree differential.

    Last, anywhere you can access it, buy some of the aluminized tape and seal any joints in the duct. It is almost criminal how sloppy some installations are.
  7. garyl53

    garyl53 Engineer

    Messages:
    54
    Location:
    Colorado
    Hi,
    While trying to track down this problem I found huge air leaks all around the main unit above the blower. I did use some foil tape to seal the seams everywhere I could reach. It has made quite a difference in the utility room. Apparently that was the coolest room in the house, but not anymore. I will check into the fan speed control to see if I can increase it. I do get good flow out of all of the other vents in the upstairs bedroom except for the one that I am adding the inline fan to.

    Gary
  8. garyl53

    garyl53 Engineer

    Messages:
    54
    Location:
    Colorado
    Oh,
    I meant to mention that all of the returns have two grills for both the 1st and 2nd floors. One is at the baseboard and another one near the ceiling but they are both on the same plenum, just one above the other. It appears the AC was added to the system sometime after the initial build of the house. Maybe I should do the same as you and block off the lower returns so all of the return air is drawn from the tops of the rooms. Should this be done on the 1st floor also? I wonder if leaving both the returns open in the "hot" bedroom would be better?
    Gary
    Last edited: Jun 15, 2007
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,817
    Location:
    New England
    If it doesn't make too much suction noise, try partially closing those downstairs so you pull more from upstairs. Try to extract that hot air at the top and you'll be better.

    One other fairly quick, simple, and inexpensive item is to put a radiant barrier on the roof joists. You can buy a roll of this fairly cheaply. It just staples up. Before I did that, at the end of a hot day, the ceiling insulation had been heatsoaked and the ceiling was hot. As soon as I put that foil-faced paper up, the ceilng was cool the next day. In the winter, it reflects heat back into the house as well. I measured my before and after average attic temperature and it dropped 30-degrees after putting in the radiant barrier...saves on a/c costs and overall comfort level is increased.
  10. garyl53

    garyl53 Engineer

    Messages:
    54
    Location:
    Colorado
    Hi All,
    Well, I put in the inline fan and it is working great! The temperature in the upstairs "hot" bedroom is now a comfortable 72 degrees. The fan is installed in the utility room in the basement feeding the duct up to the MBR. There is some noise of rushing air but you cannot hear any noise from the fan itself, even in the utility room. You actually have to touch the outside of the fan casing to tell if it is running. I used a Panasonic FV-20NLF1. In retrospect I easily could have used the lower CFM model FV-10NLF1(less expensive) and still had plenty of air movement. I might add a speed control instead of the switch that I have now so I can lower the fan speed in the evening a bit. I am surprised that just one vent feeding cold air has made such a difference in the whole room. The vents that are downstream from the duct for the fan now have decreased air movement when the fan is on but this actually works out well to balence the temperature better by putting more air upstairs. In the fall I plan to investigate the attic to see if it needs additional insulation or maybe a radiant barrier as mentioned in the thread.
    Well, thanks for the help.
    Gary
    Last edited: Jun 17, 2007
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