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  1. #27
    Join Date
    Mar 2008
    Location
    Long Beach, CA
    Posts
    3,391
    Quote Originally Posted by Cold Feet View Post



    I've got five spread between the two levels. Upstairs is served by a single 24x4 (duct size) return at the top of the stairway. The basement has four 12x4 returns--one in the hall, one each in three of the rooms. All returns in the house are mounted at floor level.

    I did some smoke tests last heating season. There's no rise up the stairway. At tread height, air goes downward into the basement. From about 2' above tread height to at least 6' above the level of the main floor, there is no air movement

    As for the basement rooms, the only air movement other than infilitration and via the supply & return registers is under the doors. This air is cold , and in two rooms, flows into the rooms from the hall. There's no hot air escaping above the doors.

    Given what I've seen with smoke tests I don't think I'm losing heat upstairs.
    There may be rise up the stairway. If air goes downward into the basement as you stated then an equal amount of heated air is escaping into the upstairs. The upstairs return may be removing this heat before it can descend to the downstairs.

    Downstairs returns are a big plus for a heating system but there is obviously more going on with your system. I said windows will not make or break a heating system but maybe yours are drafty in combination with heat rising upstairs.

    Blocking the upstairs return may yield positive results and shed light on the problem. However it may restrict the intake to the unit beyond what is recommended. But I doubt it would hurt the unit if done temporarily as a test.

    This was currently discussed extensively on another thread “suffering upstairs”. The OP blocked the downstairs return and got positive result in the AC mode. This may be your problem in reverse. But again, blocking returns should only be done if the unit is not stared for air.

    Brian

  2. #28
    Join Date
    May 2009
    Posts
    196
    Quote Originally Posted by Brian GC View Post
    The upstairs return may be removing this heat before it can descend to the downstairs.
    How would that work? Wouldn't hot air be too buoyant to sink?


    My working theory on stair airflow is that the cold downflow is air being pulled into the downstairs return registers. The rising heated air would be coming out of the upstairs supply registers.

    Naturally this is predicated on the upstairs return being undersized. I don't know enough (read: any) Manual D to figure this out conclusively but a single 26x4" (duct size) return seems a bit small for 11 6" supply registers.

    Blocking the upstairs return may yield positive results and shed light on the problem. However it may restrict the intake to the unit beyond what is recommended. But I doubt it would hurt the unit if done temporarily as a test.
    I tried that last heating season, too. Blocking the upstairs return helps the smaller, warmer, rooms but has no measurable effect on the larger, colder, rooms at the ends of the house. I don't remember what effect it had on the hall.

    Blocking the upstairs air vent increases TESP on the system from 0.31" to 0.35".



    I get another dimension to this problem at this time of year: contradictory demand from the two floors. Due to solar loading during the late afternoon, upstairs will rise to 77+ while the basement holds firm at 67. Zoning would prevent HP cooling from chilling the basement but keeping the air mixed well enough for the basement to get warmer would be better.

  3. #29
    Join Date
    Mar 2008
    Location
    Long Beach, CA
    Posts
    3,391
    Quote Originally Posted by Cold Feet View Post
    How would that work? Wouldn't hot air be too buoyant to sink?
    My theory is that if the supply adds warm air into a room and a return is not mounted high on the wall to remove it, it will continue to accumulate on the ceiling. Also, if returns are mounted low on a wall or downstairs it will continue to remove the cold strata of air on the floor or downstairs. Eventually as the downstairs cold air is removed the upstairs heated air will descend.

    Quote Originally Posted by Cold Feet View Post
    My working theory on stair airflow is that the cold downflow is air being pulled into the downstairs return registers. The rising heated air would be coming out of the upstairs supply registers.
    If cold air from upstairs is flowing down the stairs it is displacing the heated air on the downstairs ceiling, which is rising up the stairway. The same amount of air that goes down the stairs must go back up… cold down – hot up.

    Quote Originally Posted by Cold Feet View Post
    Naturally this is predicated on the upstairs return being undersized. I don't know enough (read: any) Manual D to figure this out conclusively but a single 26x4" (duct size) return seems a bit small for 11 6" supply registers.
    It does seem very small for that amount of supplies. Is that the only return or are there other returns? Do you have a single or split system? And, where are the returns mounted downstairs? Where is the unit located?

    Quote Originally Posted by Cold Feet View Post
    I tried that last heating season, too. Blocking the upstairs return helps the smaller, warmer, rooms but has no measurable effect on the larger, colder, rooms at the ends of the house. I don't remember what effect it had on the hall.
    Whenever you get near a stairway or ceiling return the heat is racing upward and leaving the room. The rooms furthest away from the stairway should be the warmest unless the supplies are weak or there is a ceiling return just outside the room.

    Your problem IMO is either volume of supplies or placement of returns. Do not underestimate the affect of returns.

    Brian

  4. #30
    Join Date
    Sep 2002
    Location
    Northeast Ohio
    Posts
    4,842
    Start with the duct system upgrade to get the available heat to the areas where it is needed (manual D). Then address the heat loss issues associated with the single pane windows. Either replace the windows as a unit, retrofit new thermal eff. sash, or at a minimum install high quality storms. Most window companies will do replacements on a piece by piece basis so you would not have to do a complete upgrade all at one time. Even though I am in the HVAC business, I tell my customers and potential customers that the smart money is in weatherization.
    A good HVAC tech knows how, an educated HVAC tech knows why!

    DEM


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