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  1. #1
    Join Date
    Apr 2007
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    27

    Add more returns or supplies to lower static pressure?

    Using Infinity 58MVB60 air handler installed the static pressure showed by Infinity thermostat display is 0.9 1.0. It seems a bit high.
    The air duct (supplies) sizes I have calculated for the 600 700 CFM by using well know HVAC Calc software tool.

    I removed the air filter insert from an air purifier GAPA body, keeping the filter compartment open letting easier for the air to get into the air handler.
    I was surprised that the static pressure went up by 0.1

    It is an old house and the ducts installation was a real pain.
    But I want to get the pressure down to appropriate 0.5 level or so.

    My question is should I add more returns or more supplies?

  2. #2
    Join Date
    Jan 2004
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    Lancaster PA
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    To know that. You ned to know if its the supply or the return or both that are causing the high static.
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  3. #3
    Join Date
    Jun 2005
    Location
    SW Wisconsin
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    5,006
    I wouldn't trust those figures. If those figures are correct the situation must be dealt with.

    Get & use an instrument you can trust to check static pressure.
    Do some SP testing to find exactly where the problem areas are.

    If you can measure the air velocity coming from a duct, here is a rough ballpark formula to get the CFM:
    CFM = (velocity in (FPM) Feet per Minute times the square footage of the duct area) - Darrell

  4. #4
    Join Date
    Apr 2007
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    27
    Thanks for your suggestions.
    I wanted to make it simpler, just making an empirical assumption.
    If the system would lack returns by opening an air filter compartment and creating additional virtual return the static pressure should drop. But instead it went up.

    Should not be enough just to assume:
    A. If by adding a supply pressure drops, it means add more supplies.
    B. If by adding more returns pressure drops, it means add more returns, but again, in this case pressure went up.
    What is wrong?

  5. #5
    Join Date
    Jun 2008
    Location
    Perry Village, Ohio
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    164
    Quote Originally Posted by udarrell View Post
    I wouldn't trust those figures. If those figures are correct the situation must be dealt with.

    Get & use an instrument you can trust to check static pressure.
    Do some SP testing to find exactly where the problem areas are.

    If you can measure the air velocity coming from a duct, here is a rough ballpark formula to get the CFM:
    CFM = (velocity in (FPM) Feet per Minute times the square footage of the duct area) - Darrell
    I did just that this weekend. I picked up a device from Grainer last friday to check the SP with various different configurations. I was able to find it after the filter, but it didn't even register anything after the coils. I must be doing something wrong. What I wanted to do was to see what the SP was at various different ducts in the basement, but it didn't even register on the testing device.

  6. #6
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    Quote Originally Posted by perrybucsdad View Post
    .
    If your supply static rises when you add return, your supply duct is also restricted.
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  7. #7
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    Quote Originally Posted by perrybucsdad View Post
    I did just that this weekend. I picked up a device from Grainer last friday to check the SP with various different configurations. I was able to find it after the filter, but it didn't even register anything after the coils. I must be doing something wrong. What I wanted to do was to see what the SP was at various different ducts in the basement, but it didn't even register on the testing device.
    What gauge/meter are you using. What kind of probes.
    Last edited by beenthere; 06-18-2008 at 09:17 AM.
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  8. #8
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    Jun 2008
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    Perry Village, Ohio
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    Quote Originally Posted by beenthere View Post
    What gauge/meter are you using. What kind of probes.
    Dwyer U Inclined http://www.grainger.com/Grainger/items/3T294. As far as the probes... That may be part of the problem. I'm not exactly sure how they are to attach. My first though was that you just slip it over the tube, but the fit is just too tight. I then noticed those red long "thingys" (sorry for the technical term). That is what I eventually used to connect it, but which end goes in the tube and which end goes in the hose, as it kept collapsing (folding over) on itself. I didn't want to ask here because of the no DIY rule, so I will more than likely just sell it since I can't seem to figure out how you use the darn thing and Dwyer has yet to answer my email.

  9. #9
    Join Date
    Jan 2004
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    Lancaster PA
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    Those long red thingys are what you put in the u tube.

    Thats not a good gauge for static testing, because its hard to see a .02 movement with it.

    Systems with very restrive returns, won't get much static pressure on the supply side of the evap coil of furnaces.
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  10. #10
    Join Date
    Jun 2008
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    Perry Village, Ohio
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    Quote Originally Posted by beenthere View Post
    Those long red thingys are what you put in the u tube.

    Thats not a good gauge for static testing, because its hard to see a .02 movement with it.

    Systems with very restrive returns, won't get much static pressure on the supply side of the evap coil of furnaces.
    Now you tell me. Okay, so what would be a better gauge to measure with, without spending a ton of bucks.

  11. #11
    Join Date
    Jan 2004
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    Lancaster PA
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    Inclined manometer. Or a Magnahelic gauge that reads pos and neg presure in tenth of inches.

    An arm and a leg to you, maybe a sprainge to me. Or vise versa.
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  12. #12
    Join Date
    Jun 2008
    Location
    Perry Village, Ohio
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    So something like the Dwyer Mark II Model 25 Incline Manometer. That was the one I wanted originally, but they didn't have it in stock. I also think there is the Binford 9000 with Flux Capacitor, leaf blower, and swiss army knife too.

    Anyone want a slightly used Dwyer?

  13. #13
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    Quote Originally Posted by perrybucsdad View Post
    So something like the Dwyer Mark II Model 25 Incline Manometer. That was the one I wanted originally, but they didn't have it in stock. I also think there is the Binford 9000 with Flux Capacitor, leaf blower, and swiss army knife too.

    Anyone want a slightly used Dwyer?
    You forgot the high powered band aid dispenser the Binford comes with.


    Donate it to your local tech school/college.
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