Page 1 of 2 12 LastLast
Results 1 to 13 of 25

Hybrid View

  1. #1
    Join Date
    Apr 2007
    Posts
    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
    Location
    Lancaster PA
    Posts
    67,770
    To know that. You ned to know if its the supply or the return or both that are causing the high static.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  3. #3
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,904
    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
    Posts
    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
    Posts
    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
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,770
    Quote Originally Posted by perrybucsdad View Post
    .
    If your supply static rises when you add return, your supply duct is also restricted.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  7. #7
    Join Date
    Jun 2008
    Location
    Perry Village, Ohio
    Posts
    164
    Quote Originally Posted by beenthere View Post
    If your supply static rises when you add return, your supply duct is also restricted.
    So what does this mean if you add more return but your supply side does not get effected at all? Still some sort of blockage in the supply side (like a dead animal )?

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,770
    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.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  9. #9
    Join Date
    Jun 2008
    Location
    Perry Village, Ohio
    Posts
    164
    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.

  10. #10
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    1,988
    Quote Originally Posted by Bordo11 View Post
    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?
    Are we to assume that you installed this system yourself?

    If you didn't, then you should be calling the installing contractor back if you have concerns about the TSP the control is showing.

    Either way you've just found out first hand one of the first basic rules of air flow in ductwork. Velocity increases static pressure.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  11. #11
    Join Date
    Jun 2008
    Location
    Perry Village, Ohio
    Posts
    164
    Quote Originally Posted by beenthere View Post

    Donate it to your local tech school/college.
    Great idea!!

    Quote Originally Posted by firecontrol View Post

    Either way you've just found out first hand one of the first basic rules of air flow in ductwork. Velocity increases static pressure.
    and so we should also conclude that dead animals in the duct work can decrease static pressure?

  12. #12
    Join Date
    Jul 2000
    Location
    Northern Wisconsin
    Posts
    1,988
    Quote Originally Posted by perrybucsdad View Post
    and so we should also conclude that dead animals in the duct work can decrease static pressure?
    No...... dead ones would increase static pressure along with increasing a few other things in the home but let's not go there.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

  13. #13
    Join Date
    Jun 2008
    Location
    Perry Village, Ohio
    Posts
    164
    Quote Originally Posted by firecontrol View Post
    No...... dead ones would increase static pressure along with increasing a few other things in the home but let's not go there.
    Okay, but they will decrease airflow after the dead animal.

    Does it increase the static pressure because the air has nowhere to go?

Page 1 of 2 12 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event