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  1. #1
    Join Date
    Jun 2010
    Northern Virginia
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    Downstairs warm, upstairs cold, but shouldn't heat be rising?

    Three story townhouse, brand new 90+ gas Ruud HVAC system, clean filter. T-stat on middle floor. Middle floor is always warm, upstairs is always several degrees colder. The colder it is outside, the larger the differential between the T-stat setting and the measured temp on the top floor. Last night I set T-stat to 73, woke up to a 67F room that felt even colder than that. Downstairs floor was toasty warm.

    Temp measured at the registers on the middle floor is 120F. Temp measured on registers on top floor is 110F, with far less airflow than the downstairs floors.

    House was built in 1985, ducts have no internal dampers that I can find. I've closed off most of the bottom floor registers to try to get the furnace to run longer and push more air upstairs, this helps a little.

    In the summer, the upstairs gets very hot, and almost no airflow can be felt from the registers. I figured this was because heat rises, but now I'm seeing the opposite problem.....

    Installation is just months old and the equipment itself appears to be ok. Furnace is a 75k RGRM Ruud model. I have no idea how the old equipment performed in this house, since I got a new system installed immediately after I moved in.

  2. #2
    Join Date
    Sep 2010
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    I would guess that air flow is poor to the upstairs. Why that is? It could be from duct work that is undersized. I take it that the furnace is located on the 1ST fl. or basement. The pressurized air will take the path of least resistance which is usually out of the registers closest to the furnace. If the duct system is designed right, the ducts going to the rooms closest to the furnace are made smaller to allow more air to reach rooms farther down the main supply duct. Your thermostat is located on the middle floor and operates the furnace with disregard to what the temp. is upstairs. If you feel very poor airflow coming out of the registers on the top floor then your problem sounds like it could be a duct size/ air balance issue. I would call an HVAC contractor to look over the duct system to see if recommendations could be made to improve air flow to the top floor. Perhaps there is space to add a supply duct to channel more air to the top floor.
    Where is the manual? What does it say?

  3. #3
    Join Date
    Jun 2010
    Philadelphia PA
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    Judging by the number of posts and your topics, it is clear you are learning the hard way that equipment is only 25% of the equation, IT'S THE SYSTEM ( THE DUCT IN THIS CASE) THAT MAKES THE SYSTEM WORK.
    So you are going to need to find someone who understands why the air is not getting to the up[stairs ( we know it is too small or the downstairs is not balanced/ dampered ) and not insulated because of the measured temp diff.
    If the contractor suggests this can all be fixed with a new return duct to the top floor, thank em and politely show them the door and don't call them back.
    Further advice, email me at my profile
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  4. #4
    Join Date
    Aug 2003
    Fort Worth, TX
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    Did you have this problem before the new system was installed?

    I encountered a two story townhome about this time last year with a similar problem as yours: top story colder than the bottom story. In this case the bottom story was not all that much warmer than the top story, but it was a head scratcher as to why the inverse temperature difference existed in the first place - as you say, heat rises and normally one expects the warmer regions to be higher in the structure.

    In the townhome's case it was a combination between airflow problems, thermostat placement, duct design, duct leakage, and large heat losses from the building's upper story walls and ceilings due to poor or missing insulation. Not to mention a rather nasty stack effect - I measured 8 - 10 pascals positive air pressure at the second story ceiling adjacent to the attic pulldown stairs - air was moving through that house like it had a forced draft blower.
    Building Physics Rule #1: Hot flows to cold.

    Building Physics Rule #2:
    Higher air pressure moves toward lower air pressure

    Building Physics Rule #3:
    Higher moisture concentration moves toward lower moisture concentration.

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