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  1. #1
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    Traversing stainless steel duct

    New here and sorry if this topic has already been covered, but what is protocol on traversing stainless steel duct? Is it an acceptable practice?

    Doing a survey on a hospital and don't have the time to go measure all the lab hoods and phoenix exhaust valves.

  2. #2
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    I'm not a TAB guy but I don't see any difference. Airflow is airflow. Take your reading in the correct locations and should be no issues.

    What does your contract require you to record? You are in a hospital but don't have time to make sure hoods are safe to work in?

  3. #3
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    Quote Originally Posted by Push It View Post
    I'm not a TAB guy but I don't see any difference. Airflow is airflow. Take your reading in the correct locations and should be no issues.

    What does your contract require you to record? You are in a hospital but don't have time to make sure hoods are safe to work in?
    Lab hoods / exhaust system works fine. Conducting an overall air flow survey on air handlers, return fans, and exhaust systems.
    The building has a huge negative pressure and the client wants a snapshot of the air systems. I know that stainless steel used for kitchen hood purposes produce high temperature and is thus frowned upon of doing a duct traverse. Not sure if the chemicals used here could potentially pose a problem with drilling holes in the duct.

  4. #4
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    Do not drill holes in the kitchen hood unless provisions have been made to have the holes seal welded. The same goes for any duct that carries anything that can be hazardous. If the building is negative you have too much exhaust or not enough outside air.
    To be perfectly honest the hospital should hire a balance contractor.
    No man can be both ignorant and free.
    Thomas Jefferson

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  6. #5
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    My method to figure out negative buildings is very simple and I have used it many times . I start at each exterior door at all four sides of the building to confirm the building is actually negative . Sometimes you can have air going in on one side of the building and air going out on the other side . Especially if the building is not sealed well and it is windy . It can also have air going in one side and out the other due to the different compartments / new wing additions. After confirming the building is negative I just follow the air through the building by closing one set of double doors at a time . Following the air takes you right to the negative area , usually the kitchen . In my opinion measuring all the outside air and exhaust is usually the last thing I would do . Following the air and finding the culprit area is much more effective .

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  8. #6
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    Quote Originally Posted by freqdrive View Post
    Lab hoods / exhaust system works fine. Conducting an overall air flow survey on air handlers, return fans, and exhaust systems.
    The building has a huge negative pressure and the client wants a snapshot of the air systems. I know that stainless steel used for kitchen hood purposes produce high temperature and is thus frowned upon of doing a duct traverse. Not sure if the chemicals used here could potentially pose a problem with drilling holes in the duct.
    Hospitals ARE negative pressure by design. The closer you get to the nasty bugs the more negative it gets.


    You need toe a little more specific!

  9. #7
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    I have drilled stainless steel ducts for traversing multiple times . As noted previously , welding the holes is the best way . However , I have use 3/8" boiler plugs to seal the holes . They are a threaded steel body with a high temperature rubber gasket . Also......Hospitals are designed neutral by design here in Florida and that's what the AHCA inspectors want to see . I usually "tweek" the outside air a bit ( after they leave ) to make the building slightly positive just to be safe . A negative building is a disaster with all of the humidity here . The problem with leaving a building neutral is it doesn't take much " drift " from the control systems or dirty filters not changed to swing it to the negative side . Its a case of giving them what they need , not what they think they want .

  10. #8
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    Just about every commercial kitchen I see has a negative balance.
    It's always the exhaust is way more then the make-up.

  11. #9
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    All kitchens should be slightly negative , it keeps the odors in the kitchen .

  12. #10
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    Quote Originally Posted by bradluke0 View Post
    I have drilled stainless steel ducts for traversing multiple times . As noted previously , welding the holes is the best way . However , I have use 3/8" boiler plugs to seal the holes . They are a threaded steel body with a high temperature rubber gasket . Also......Hospitals are designed neutral by design here in Florida and that's what the AHCA inspectors want to see . I usually "tweek" the outside air a bit ( after they leave ) to make the building slightly positive just to be safe . A negative building is a disaster with all of the humidity here . The problem with leaving a building neutral is it doesn't take much " drift " from the control systems or dirty filters not changed to swing it to the negative side . Its a case of giving them what they need , not what they think they want .
    How does negative pressure create humidity issues?

    DO YOU HAVE DOCUMENTS SUPPORTING YOUR CLAIMS. Neutral!

    I’m sure the local authorities having jurisdiction would love to hear leaving them slightly positive

  13. #11
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    Quote Originally Posted by bradluke0 View Post
    All kitchens should be slightly negative , it keeps the odors in the kitchen .
    I'm not talking "slightly" I'm talking BIG difference as in large negative pressure. The kind where it's hard to open the doors.
    I see it all the time probably 75 % .

  14. #12
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    I trace pressure profiles with a cigarette lighter. The cheapest and most accurate tool for that purpose in the world. I have done it so much I can normally estimate the pressure pretty close.
    A school I balanced had a room that got so cold it froze the sprinkler pipes. I told the GC his building was leaking severely above the ceiling and he took offense until he saw the infiltrating air blow my lighter out.
    I have seen more negative buildings than positive ones. Dogs and cats get along better than a negative building with electric reheat.
    No man can be both ignorant and free.
    Thomas Jefferson

  15. #13
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    Quote Originally Posted by WAYNE3298 View Post
    I trace pressure profiles with a cigarette lighter. The cheapest and most accurate tool for that purpose in the world. I have done it so much I can normally estimate the pressure pretty close.
    A school I balanced had a room that got so cold it froze the sprinkler pipes. I told the GC his building was leaking severely above the ceiling and he took offense until he saw the infiltrating air blow my lighter out.
    I have seen more negative buildings than positive ones. Dogs and cats get along better than a negative building with electric reheat.
    I agree , a lighter is the bomb for chasing pressurization . Also , sticking your nose in a door that's open a few inches works great too . I'm not sure I have seen more negative buildings than positive ones but I have seen a bunch . Dogs and cats also get along better than a negative building and Florida humidity ( great line there Wayne , had to use it ….lol )

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