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
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 02:58 AM.
Love makes the world go around but cash pays the bills
This is governed by NFPA 96 and the UMC.......
AS USUAL Check with you local code authority
126.96.36.199 Eybrow-type hoods over gas or electric ovens shall bethe exhaust plenum as shown in Figure 5.1.6.
permitted to have a duct constructed as required in Chapter 7
from the oven flue(s) connected to the hood canopy upstream of
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 08:45 PM.
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
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?
505.1.1 Commercial cooking appliances vented by exhaust hoods.
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
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
Last edited by zzonko; 09-14-2008 at 11:21 PM.
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.
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
Last edited by zzonko; 09-16-2008 at 10:07 PM.
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.
Originally Posted by PaysonHVAC
You will also be voiding the CSA and UL listings for the equipment and assuming some liabilities that you don't want.
True Heavy Metal Geek