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  1. #1
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    Uh... I'm not so sure this is a good idea. Flue tied to kitchen hood!

    Today the boss had me stop by one of our restaurants that we service to take measurements for them and see what it is exactly they wanted done.

    Well turns out the general manager for this chain wants these exhaust (flues) extended and ran directly up into this exhaust hood's intake to the exhaust fan.








    That is a Pizza oven and a bread oven on the right.






    The managers in the store said they think NOTHING is wrong as you can feel the heat radiating from the ovens ONLY if you stand right against them, but otherwise everything is exhausting normal.

    For some reason the general manager thinks them flues should be ran up into the intake of that exhaust hood. I guess he is thinking it will run cooler. The managers in the store think it will have ZERO effect on the heat radiating from the ovens themselves, and I agree.

    I've never been asked to do such a thing and it is working properly as it is supposed to.

    But one scary thought came to mind when I was measuring to extend the pipe...

    What happens if you actually run the flues directly into that intake in the middle of the hood? Will the extra "induced draft" cause something bad with the burners?

    I just don't think it's a good idea. And come Monday I need to go back for something else, and plan on writting up my recommendation. Most likely that it is a BAD idea to directly couple the flue vents to the exhaust intake!

    What do you guys think?
    True Heavy Metal Geek

  2. #2
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    I agree with it being a bad idea, my thought is the pilot lights may be sucked out so to speak and have gas build up, I could be wrong but /shrug it is still a bad Idea in my opinion.

    PS. It may be a good idea to check the local fire codes etc.
    Last edited by Kelly T; 09-13-2008 at 01:58 AM. Reason: afterthought
    Love makes the world go around but cash pays the bills

  3. #3
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    Quote Originally Posted by Kelly T View Post
    I agree with it being a bad idea, my thought is the pilot lights may be sucked out so to speak and have gas build up, I could be wrong but /shrug it is still a bad Idea in my opinion.

    PS. It may be a good idea to check the local fire codes etc.
    Ya know. I didn't look to see if it had any pilot light. But it probably does use them.

    Man. Being that the thing works with natural draft, I just wonder how that thing may fire off with that much air pulling through it at all times!

    Could be interesting. At least the managers who work in that restaurant are not the ones wanting this done.
    True Heavy Metal Geek

  4. #4
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    This is governed by NFPA 96 and the UMC.......

    AS USUAL Check with you local code authority


    5.1.8.1 Eybrow-type hoods over gas or electric ovens shall be
    permitted to have a duct constructed as required in Chapter 7
    from the oven flue(s) connected to the hood canopy upstream of
    the exhaust plenum as shown in Figure 5.1.6.


    http://www.nfpa.org/assets/files/PDF...-A2001-rop.pdf

    PAGE 7 figure 5.1.6

    AND Chapter 7 Page 9


    The flue has to be upstream in the hood and the front of the hood has to be 10" further out than the ovens

    Also...Hood ducts for grease applications need to be continously welded 16ga and CANT be "a" or "b" vent pipe like the one in your pic (cant tell from pic but there is grease in that duct connection)
    Last edited by zzonko; 09-13-2008 at 07:45 PM.

  5. #5
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    So, all in all, looking at the overns under that hood, which is all working PERFECTLY FINE, would you extend the over flues up into that exhaust intake thus causing an induced draft through the burners of each oven!
    True Heavy Metal Geek

  6. #6
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    That is one I probably would walk from as it seems to be out of compliance to begin with. But from what you post arent most things out there?

    http://phoenix.gov/devserv/fuel_gas_pkg.pdf



    505.1.1 Commercial cooking appliances vented by exhaust hoods.
    Where

    commercial cooking appliances are vented by means of the Type I or Type II kitchen

    exhaust hood system that serves such appliances, the exhaust system shall be fan
    powered and the appliances shall be interlocked with the exhaust hood system to
    prevent appliance operation when the exhaust hood system is not operating. Where a
    solenoid valve is installed in the gas piping as part of an interlock system, gas piping
    shall not be installed to bypass such valve. Dampers shall not be installed in the
    exhaust system.







    .


    It does need to be interlocked between the fan and gas pipe solenoid. Also it would seem Phoenix_Gov requires welded 16g duct and not "a" or "b" vent as there is grease present. Its all below


    506.3.10







    Last edited by zzonko; 09-14-2008 at 10:21 PM.

  7. #7
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    Quote Originally Posted by zzonko View Post
    That is one I probably would walk from as it seems to be out of compliance to begin with. But from what you post arent most things out there?



    Other than the missing filter in the hood, it operates fine as it is.

    We don't even know WHY the general Manager wants to have the flues extended up into the hood duct.

    We think that maybe he's thinking it will keep the oven exterior cool, or something.
    But if you step back 20" from the oven, you don't even feel the heat. I don't even think anyone in the restaurant was complaining. The GM was in there and came up with that on his own.

    I still don't think pulling a continuous draft through the flues is a good idea. Dunno what would happen upon ignition until they try it!
    True Heavy Metal Geek

  8. #8
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    Wouldn't this make your company liable for any damage or injury? That equipment had to be certified for safety before it could be marketed. Altering the way the equipment performs would most likely void any certifications the manufacture received.

  9. #9
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    Quote Originally Posted by coldking View Post
    Wouldn't this make your company liable for any damage or injury? That equipment had to be certified for safety before it could be marketed. Altering the way the equipment performs would most likely void any certifications the manufacture received.
    So what you are saying is we'd pretty much need to DENY doing the flue extensions that the GM of the restaurant is asking for??

    Aside from liability and all...
    What do you think of the effect overall of coupling the flues right up into the exhaust intake thus causing an induced draft through the burners?

    I'd wonder if it would change the fuel to air ratio, cause ignition problems, etc...
    True Heavy Metal Geek

  10. #10
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    Did you look at the diagram in nfpa 96? As it is now it does not comply.the top of the flue has to be above the bottom plane of the hood.

    Usually a pizza oven is a class 2 hood design, The presence of grease in that top connection turns it into a class 1 meaning that a fire suppression system is also missing and that the duct going to the fan needs to be 16g continuosly welded not "a" vent like that one. Oven flues are vented into hoods all the time (dont forget the interlock!)

    You also need to have a engineer stamped drawing to modify or construct hood systems. All info you need is in the above links I listed above

    Phoenix 2006 Mech Code
    page 22 section 507
    http://www.archive.org/download/gov....mechanical.pdf



    good luck
    Last edited by zzonko; 09-16-2008 at 09:07 PM.

  11. #11
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    Quote Originally Posted by zzonko View Post
    Did you look at the diagram in nfpa 96? As it is now it does not comply.the top of the flue has to be above the bottom plane of the hood.

    Usually a pizza oven is a class 2 hood design, The presence of grease in that top connection turns it into a class 1 meaning that a fire suppression system is also missing and that the duct going to the fan needs to be 16g continuosly welded not "a" vent like that one. Oven flues are vented into hoods all the time (dont forget the interlock!)

    You also need to have a engineer stamped drawing to modify or construct hood systems. All info you need is in the above links I listed above

    Phoenix 2006 Mech Code
    page 22 section 507
    http://www.archive.org/download/gov....mechanical.pdf



    good luck
    I did look, but didn't understand until just now that you were saying those vents needed to be right up under the hood.

    Exhaust hoods and ovens are not my specialty. In fact as a company we don't even touch the "hot work". Although I did some of it in my first few yrs of learning when I worked in Payson, AZ.

    Why would there be grease in a pizza and bread oven anyway?

    And could you explain why the vents should be higher than the bottom lip of the hood, and what the benefit of doing that is?
    I'm curious. Even though I am going to try to talk our way out of doing this.
    True Heavy Metal Geek

  12. #12
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    Quote Originally Posted by PaysonHVAC View Post
    I did look, but didn't understand until just now that you were saying those vents needed to be right up under the hood.

    Exhaust hoods and ovens are not my specialty. In fact as a company we don't even touch the "hot work". Although I did some of it in my first few yrs of learning when I worked in Payson, AZ.

    Why would there be grease in a pizza and bread oven anyway?

    And could you explain why the vents should be higher than the bottom lip of the hood, and what the benefit of doing that is?
    I'm curious. Even though I am going to try to talk our way out of doing this.
    A small amount of grease, dirt, or possibly cigarette smoke tar is on the duct, but there is no cooking equipment below the hood that would require the class 1 features. I agree that the flue's from the 2 pieces of equipment should be extended just above the bottom of the hood. That's probably what your GM wants done. This much extension will not affect the draft significantly and keeps the flue gas contained within the hood - which is good. Taking them up and into the duct itself is not a good idea because of the draft problems, pilot problems, and also because you will reduce the exhaust air that is removing warm air from around the outside of the ovens.

    You will also be voiding the CSA and UL listings for the equipment and assuming some liabilities that you don't want.

  13. #13
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    Quote Originally Posted by bob_scheel View Post
    A small amount of grease, dirt, or possibly cigarette smoke tar is on the duct, but there is no cooking equipment below the hood that would require the class 1 features. I agree that the flue's from the 2 pieces of equipment should be extended just above the bottom of the hood. That's probably what your GM wants done. This much extension will not affect the draft significantly and keeps the flue gas contained within the hood - which is good. Taking them up and into the duct itself is not a good idea because of the draft problems, pilot problems, and also because you will reduce the exhaust air that is removing warm air from around the outside of the ovens.

    You will also be voiding the CSA and UL listings for the equipment and assuming some liabilities that you don't want.
    Yeah it looks like the GM musta been confused with extending them higher just into the hood with extending them into the duct!
    He wanted it extended into the duct!

    I talked to our guy who does the bids and IF we extend them, I think he'll just have me extend them straight up into the hood area only.

    We're still wondering why we are involved. We don't do "hot work". But we do repair the exhaust fans, etc.
    Looks like we drew the shortest straw between us and the co. who does the ovens.
    True Heavy Metal Geek

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