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  1. #1
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    Question Forced air - uneven heating this winter

    I have a 1974 2-story house with a half basement that is heated with an oil-fired forced hot air system. There are 3 bedrooms on the second story. Two of them can get ridicculously hot while the third is rather cool. The 2 hot bedrooms have 2 registers each while the 3rd cool room (the smallest of the 3) has 1 register. I have tried closing off some of the registers in the other bedrooms and downstairs as well to push more hot air upstairs to the cool bedroom, but that hasn't helped. BTW, all the windows have been replaced with high-efficiency models.

    Any thoughts? Could the ductwork going to that 3rd bedroom be clogged?

  2. #2
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    Default Re: Forced air - uneven heating this winter

    Has it always been like that or has it gradually gotten worse over time? Is there any air at all coming out of the supply? Is that bedroom the last run off the main Supply trunk and if it is does the run come right off the end or is it about 18 inches back from the end of the main? Did you check the dampers that are in the supply takeoffs? I doubt it's clogged but then again anything is possible. How is your main trunk configured, is it all one size or is it a reducing trunk. All main trunks should reduce one size every two to three runs, I prefer every two, this must be done to keep pressure within the trunk. No pressure no air. Check these things out and get back to us, Good Luck

  3. #3
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    Default Re: Forced air - uneven heating this winter

    Quote Originally Posted by lekmedm View Post
    The 2 hot bedrooms have 2 registers each while the 3rd cool room (the smallest of the 3) has 1 register.
    Where's the return air coming from for the small, cold, room? What are the registers in the other rooms? Two supply, or one supply and one return?

    If a room can't effectively turn over it's air then it won't matter if the duct INTO the room is clear or not. Air has to get pulled OUT of the room too in order for the air handling system to work properly.

  4. #4
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    Default Re: Forced air - uneven heating this winter

    I replied a couple of days ago, but it looks like it got lost, so let's try again...

    Quote Originally Posted by Sten View Post
    Has it always been like that or has it gradually gotten worse over time? Is there any air at all coming out of the supply? Is that bedroom the last run off the main Supply trunk and if it is does the run come right off the end or is it about 18 inches back from the end of the main? Did you check the dampers that are in the supply takeoffs? I doubt it's clogged but then again anything is possible. How is your main trunk configured, is it all one size or is it a reducing trunk. All main trunks should reduce one size every two to three runs, I prefer every two, this must be done to keep pressure within the trunk. No pressure no air. Check these things out and get back to us, Good Luck
    Has it always been like that or has it gradually gotten worse over time?

    I think it's always been like this.

    Is there any air at all coming out of the supply?

    Yes.

    Is that bedroom the last run off the main Supply trunk and if it is does the run come right off the end or is it about 18 inches back from the end of the main?

    Whoa, now you're getting into the heavy-duty pro questions. My best guess is , yes, it's the last run, but that's just a guess. How can I find out for sure?

    Did you check the dampers that are in the supply takeoffs?

    The dampers where, now...? Are you talking about in the basement near the furnace?

    I doubt it's clogged but then again anything is possible. How is your main trunk configured, is it all one size or is it a reducing trunk.

    I believe the answer is that it is a reducing trunk. That's how it appears to me in the basement, and that's how it looked when my master bath was renovated and the subfloor was removed.

    Quote Originally Posted by wkearney99 View Post
    Where's the return air coming from for the small, cold, room? What are the registers in the other rooms? Two supply, or one supply and one return?

    If a room can't effectively turn over it's air then it won't matter if the duct INTO the room is clear or not. Air has to get pulled OUT of the room too in order for the air handling system to work properly.
    Where's the return air coming from for the small, cold, room?

    There is no return in the wall of the small, cold room. The room is rather cool all day with the door open, so it's not just a closed space phenomenon.

    What are the registers in the other rooms? Two supply, or one supply and one return?

    The master bedroom has 2 supplies and 2 returns. The second bedroom has 2 supplies and at least 1 return (maybe 2).






    Thanks for taking an interest and helping me with this!

  5. #5
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    Default Re: Forced air - uneven heating this winter

    The dampers are in the supply takeoffs that are on the main trunk, this is where you do your balancing.
    Does it seem like there's a lot or little air coming from the supply at the coldest room.
    Check the supply temps. at all your supplies.
    What is the total length of duct and supply run from the furnace to the cold room.

    You may need another return, your furnace could be undersized (BTU's). To check and see if the last supply is coming off the end or is 12-18 inches back from the end you have get to where it comes off the main trunk an look at it.

  6. #6
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    Default Re: Forced air - uneven heating this winter

    Quote Originally Posted by lekmedm View Post
    There is no return in the wall of the small, cold room. The room is rather cool all day with the door open, so it's not just a closed space phenomenon.

    The master bedroom has 2 supplies and 2 returns. The second bedroom has 2 supplies and at least 1 return (maybe 2).
    The open door and still cool phenomenon makes wonder how poorly that room is insulated. Perhaps an inspection by someone with a thermal imaging camera could shed some light on that.

    And since the other rooms have better supply/return setups I'd really start to wonder about how well the system is designed with regard to heating that room. I'm no HVAC expert but it seems like it'd be a good idea to have one come do some testing. Like measuring airflow and temperatures at all the registers.

    Meanwhile have you done simple things like making sure all the ducts are attached and properly sealed? I had one house with really marginal heating in a few rooms that was due to a tremendous amount of airflow being lost. There were lots of small leaks where nearly every duct was joined, and one that had nearly fallen completely out! A few hours with some foil tape made it a lot more livable.

  7. #7
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    Default Re: Forced air - uneven heating this winter

    Quote Originally Posted by Sten View Post
    The dampers are in the supply takeoffs that are on the main trunk, this is where you do your balancing.
    What do the dampers at the supply look like? I've looked at the furnace and ducting, but I don't see any dampers. Maybe I just don't know where to look?

  8. #8
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    Default Re: Forced air - uneven heating this winter

    Go to the Main trunk and follow it to the supplies that go to diff. rooms. The dampers are in the takeoffs that the supplies are attached to, the takeoff itself is attached to the main. There should be a handle that tells the direction of the damper, parallel open, perp. closed, if your supplies are insulated the handle may be covered with insulation. Feel for it through the ins., if they are covered make a slight cut and expose the handle, they shouldn't be covered anyway. This is where you should be making you air flow adjustments. If there are no dampers then some one screwed up, there should all ways be dampers in supply takeoffs and none in return takeoffs. Good Luck

  9. #9
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    Default Re: Forced air - uneven heating this winter

    OK, I'm going to ask a stupid question now...

    How am I supposed to check along the lines when everything is behind the walls and floors...?

  10. #10
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    Default Re: Forced air - uneven heating this winter

    I really don't know how to explain it any clearer, The dampers are inside the takeoffs which are attached to the main trunk, can you see the main trunk, it's the thing that comes from the furnace.

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