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  1. #1
    Join Date
    Jul 2008
    Location
    Richmond, Virginia
    Posts
    25

    Closing supply registers

    This may have been discussed previously but is it OK to close several 1st floor supply registers to increase airflow to 2nd story or would this potentially be dangerous to my system?

    I have a single speed fan and one system ....I am trying to accomplish additional airflow to bedroom that is most distant from evaporator coil.

    Thanks for you help.

  2. #2
    Join Date
    Aug 2007
    Posts
    72
    I've been doing that for years with no apparent ill effects.

  3. #3
    Join Date
    Mar 2007
    Location
    Myrtle Beach, SC
    Posts
    2,919
    In a word....NO.

    Closing downstairs registers does increase duct static pressure, so it will help your upstairs registers. But if you look at the blower chart, you will see that as duct static increases, overall air flow goes down. This is because there is more resistance to air flow in the duct system.

    You can measure this with a anemometer or flow hood as well.

    As you reduce air flow below its rated value, you reduce capacity, efficiency, and life of the compressor. If there are any supply air leaks in the ducts, then duct leakage will go up as well, further aggravating your problems. So don't do it.
    Remember, Air Conditioning begins with AIR.

  4. #4
    Join Date
    Aug 2007
    Posts
    72
    Quote Originally Posted by Kevin O'Neill View Post
    In a word....NO.

    Closing downstairs registers does increase duct static pressure, so it will help your upstairs registers. But if you look at the blower chart, you will see that as duct static increases, overall air flow goes down. This is because there is more resistance to air flow in the duct system.

    You can measure this with a anemometer or flow hood as well.

    As you reduce air flow below its rated value, you reduce capacity, efficiency, and life of the compressor. If there are any supply air leaks in the ducts, then duct leakage will go up as well, further aggravating your problems. So don't do it.

    Most two-story homeowners like me are stuck with a single-zone system, so we make the best of what we have.

    In my house, the 2nd floor gets too warm with all the downstairs registers wide open in summer. One has to turn the thermostat down 2-3 more degrees to make the 2nd floor comfortable, thereby making lower floors too cold.

    In summer, I close five of the ten first-floor registers, and all three in the finished basement. This significantly helps make the 2nd floor more comfortable. This is the configuration the system is in when the tech does his annual checks for the past 8 years, and the system operating parameters aren't out-of-whack. So I don't think I'm hurting anything.

  5. #5
    I agree with PowerPlay, I ran my old system for over fifteen years with three registers closed on the first floor and never experienced any problems.

  6. #6
    Join Date
    Sep 2002
    Location
    I don't know
    Posts
    2,897
    It really depends on if you're duct system and airflow is marginal to begin with.

    A good strategy is to slightly damper down the first floor vents instead of closing them.

    Systems which have excess blower capacity (Ex: 2 or 2.5 ton unit on a 3 ton drive furnace) in my opinion won't get damaged by closing vents, provided that the blower speed tap is selected only after balancing. (Close appropriate vents first, then set up blower to move 400 CFM/ton based on static pressure)

    I have dampered down vents with no ill effects.
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

  7. #7
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Quote Originally Posted by Kevin O'Neill View Post
    In a word....NO.

    Closing downstairs registers does increase duct static pressure, so it will help your upstairs registers. But if you look at the blower chart, you will see that as duct static increases, overall air flow goes down. This is because there is more resistance to air flow in the duct system.

    You can measure this with a anemometer or flow hood as well.

    As you reduce air flow below its rated value, you reduce capacity, efficiency, and life of the compressor. If there are any supply air leaks in the ducts, then duct leakage will go up as well, further aggravating your problems. So don't do it.
    True for the most part,however in a properly designed duct system,you can reduce air flow,not close them off,by up to 25% on 33% of the grilles,with little effect.

  8. #8
    Join Date
    Mar 2008
    Location
    Central Maryland
    Posts
    246
    Quote Originally Posted by VA GENT View Post
    This may have been discussed previously but is it OK to close several 1st floor supply registers to increase airflow to 2nd story or would this potentially be dangerous to my system?

    I have a single speed fan and one system ....I am trying to accomplish additional airflow to bedroom that is most distant from evaporator coil.
    I'm in the same position as you, upstairs too hot, one unit, single zone.

    I used to close off up to 1/2 of my main floor registers, and two supply registers in better cooled rooms upstairs. I still had 8 to 10 degree temp delta between top and main floor, especially in one room. I left the balance doors alone as I had heard not to mess with them. They used to be 30 and 40% closed. I don't do any of that any more.

    Now I rebalance for Summer with the upstairs supply at 100% open and the downstairs at 75% (25% blocked). I also have both basement registers on that supply open as well, because the basement needs dry air and air circulation.

    I addition I opened ALL my top floor registers, even if that room is getting plenty of cool air. I also took care to make sure both upstairs returns are free and clear of obstruction. This helps push hot air into the returns, which is just as important as getting plenty of cool air up there. I do have one downstairs supply register closed, the one furthest from the unit.

    As a result, the upstairs now has a temp differential of 4 degrees average/6 degrees tops on the sunniest, hottest days. I think this is about as good as it gets.

    I am looking into adding more returns from the upstairs, or at least increasing the grill size of the returns I already have. I don't kid myself, it will only be worth one degree, maybe two if I'm lucky, but my furnace will enjoy the extra air, and I'll enjoy that 1 or 2 degrees.

    -HF

  9. #9
    Join Date
    Mar 2008
    Location
    Jackson, NJ
    Posts
    176
    Quote Originally Posted by hangfirew8 View Post
    I'm in the same position as you, upstairs too hot, one unit, single zone.

    I used to close off up to 1/2 of my main floor registers, and two supply registers in better cooled rooms upstairs. I still had 8 to 10 degree temp delta between top and main floor, especially in one room. I left the balance doors alone as I had heard not to mess with them. They used to be 30 and 40% closed. I don't do any of that any more.

    Now I rebalance for Summer with the upstairs supply at 100% open and the downstairs at 75% (25% blocked). I also have both basement registers on that supply open as well, because the basement needs dry air and air circulation.

    I addition I opened ALL my top floor registers, even if that room is getting plenty of cool air. I also took care to make sure both upstairs returns are free and clear of obstruction. This helps push hot air into the returns, which is just as important as getting plenty of cool air up there. I do have one downstairs supply register closed, the one furthest from the unit.

    As a result, the upstairs now has a temp differential of 4 degrees average/6 degrees tops on the sunniest, hottest days. I think this is about as good as it gets.

    I am looking into adding more returns from the upstairs, or at least increasing the grill size of the returns I already have. I don't kid myself, it will only be worth one degree, maybe two if I'm lucky, but my furnace will enjoy the extra air, and I'll enjoy that 1 or 2 degrees.

    -HF
    Try closing the vent closest to the stat. I only have 3 vents shut down in the whole house; upstairs is 75 downstairs is 74. One or two downstairs are dampened 1/3 of the way too.

  10. #10
    Join Date
    Mar 2008
    Location
    Central Maryland
    Posts
    246
    Quote Originally Posted by Jopopsy View Post
    Try closing the vent closest to the stat. I only have 3 vents shut down in the whole house; upstairs is 75 downstairs is 74. One or two downstairs are dampened 1/3 of the way too.
    I thought of that.

    I could also put a lamp under the thermostat.

    -HF

  11. #11
    Join Date
    Jun 2008
    Posts
    25
    I too had a warmer upstairs. Solved ( or improved) the problem by adding a "booster fan" inside the upstars return duct. This booster, controlled by an air flow switch, helps remove the warmer upstairs air and really improves the cooling comfort level. Also, running the system fan constantly helps alot.

  12. #12
    I had the same problem in an open foyer design, so all the cold air upstairs just ran right down the stairs directly on top of the thermostat making the problem even worse due to short cycling. I had a 7 degree difference between the 1st and 2nd floors and had to run my stat at 68 degres downstairs to sleep at 75 upstairs at night. My solution was to install a solar attic fan, which lowered the attic temperatures by almost 30 degrees, but more importantly redued the total heat gain in the attic and greatly reduced the heat loading on the upstairs ceiling. We also had poor airflow out of the upper registers with only a 1/3 HP fan motor on a 3.5 ton system most likely due to poor duct design. We increased the blower motor to a 3/4HP motor at the same rpm rating, but now the blower has plenty of power to push through the increased SP and get air upstairs. I only open the furthest registers away from the Tstat on the first floor now and have a 2 degree delta T now between floors. I now run my stat at 75 setting on the first floor and have saved over 700 kWh on my June 2008 bill vs. June 2007. May savings was similar. Needless to say I am a happy camper. Sometimes you have to work around what you were given if the basement is finished and adding zone control is not an option.

  13. #13
    Join Date
    Aug 2006
    Posts
    11
    Consider upgrading the insulation in the attic above the second floor, could make some difference. With the rising costs of fuel, every bit will help.

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