Kitchen exhaust duct materials?
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  1. #1
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    Kitchen exhaust duct materials?

    Howdy! Still working on our hvac and love all the help here.
    So we're installing a Wolf 1500 cfm remote blower with about 25' of 10" duct with (5) 90 elbows. What gauge metal do I need and does stainless do much for the upgrade in price? Will galvanized hold up for 50 yrs? What insulation do I need? R-4? And lastly are screws ok to use to connect ducts or do they create a grease trap?

    Thanks much

  2. #2
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    This is a commercial kitchen with lots of make-up air and a fire extinguishing system, right? So the mechanical engineer on the job should be spec-ing out the materials. But you should upsize your heating and cooling systems to accommodate the make-up air. Let's see, 1500 CFM, 1500 CFM, yup, that's a need to at least an additional 4-tons of AC. How long will that fan be running? I'd go with stainless whenever possible. It's a little more slippery than galvy and the air moves easier.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  3. #3
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    Grease duct is 16 gauge black iron, or 18 gauge stainless steel, no screws, all seams welded liquidtite. Clearances are 18" from combustibles and 3" from gypsum. Clearance reduction is accomplished with Fyrewrap insulation or fire chase. System needs to be engineered




    Quote Originally Posted by rsspencer View Post
    Howdy! Still working on our hvac and love all the help here.
    So we're installing a Wolf 1500 cfm remote blower with about 25' of 10" duct with (5) 90 elbows. What gauge metal do I need and does stainless do much for the upgrade in price? Will galvanized hold up for 50 yrs? What insulation do I need? R-4? And lastly are screws ok to use to connect ducts or do they create a grease trap?

    Thanks much

  4. #4
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    Jan 2010
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    SW WA
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    Nah, it's for a residence. Just a big 80k btu grill and the manufacturer says 1,100 cfm and I figure after it gets through the duct and elbows, the 1,500 will be more like 800 cfm or so. The cfm isn't the issue though as I already have the fan but need to know what kind of duct (galvanized, stainless, etc) and what gauge (18ga, 26 ga, 30ga) and how to connect them (screws, metal straps, high temp tape, ?).
    Thanks for any light you can shed.

  5. #5
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    Note to the OP. reread the direrections and learn threory

  6. #6
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    better yet hire a qualified contractor

  7. #7
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    You don't have any nd appliances, or a fireplace, do you? Plan for make up air is...?
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  8. #8
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    Thumbs up

    Quote Originally Posted by tedkidd View Post
    You don't have any nd appliances, or a fireplace, do you? Plan for make up air is...?
    Did you mean NG? If so, yes we have gas appliances and a fireplace. I appreciate the concern for the whole system. However, the MUA is being professionally engineered and though complicated and expensive will be adequately addressed and professionally installed. Just the actual range exhaust duct is something we are in a bind to rush to get installed ourselves this week. But we don't what type of duct material to use (stainless vs. galvanized vs. ?), how thick it has to be (18ga-30ga) nor if we can use screws for the connections, or if we have to weld them or if we can metal strap them or what. As well as how much insulation. R-4? If someone good give us a little guidance with those, that would be great! Anticipated Thanks, Scott

  9. #9
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    No, I meant natural draft (ie, not sealed combustion, not power vented, pulls air from the house, gravity fed). Backdrafting your fireplace is unpleasant, but likly to be quickly noticed. Flame rollout on your water heater could burn the house down.

    Skip touched on need for 1500 cfm makeup air. If this is being professionally engineered they will have make up air coming in somewhere. Otherwise, the question to ask is what credentials are behind the lable "professional".

    Leaving make up air to chance, to the hope you have and always will have a crappy, loose house isn't just sloppy, it's dangerous. (a house that has natural draft appliances and can afford another 1500 cfm without causing problems is a corn crib). What if you later decide to weatherize this corn crib? That device needs to stand on it's own irrespective of how you may change the house.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  10. #10
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    Jan 2010
    Location
    SW WA
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    Thanks for the concern, TK. The PE designing is really good and does forensic work too so has examined why systems don't work as well. I'm confident the MUA will be fine. My concern the what to use to put together the exhaust. The PE isn't avail for questions for a while and I have to install the exhaust a.s.a.p.
    TIA Scott

  11. #11
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    Rochester NY
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    Rs - this is a public bb where people come to learn. When you make a post and brush by an important issue, particularly health and safety, it's incumbent upon us to make sure the potential error is clear.

    While you may be fully aware of the tremendous hazard a huge exhaust fan can create, if it is not clear to others interested in the topic we may put them at risk if it is not called out.

    It is not just about taking free consulting to solve your particular problem, by participating you have an obligation to give too. After you receive what you need this post lives on, and you are the one responsible for it. It could potentially cause or prevent harm depending on the content. Which would you prefer?
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  12. #12
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    Jun 2005
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    Near Chicago, IL
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    3,317
    Quote Originally Posted by rsspencer View Post
    Thanks for the concern, TK. The PE designing is really good and does forensic work too so has examined why systems don't work as well. I'm confident the MUA will be fine. My concern the what to use to put together the exhaust. The PE isn't avail for questions for a while and I have to install the exhaust a.s.a.p.
    TIA Scott
    MUA is not fine if it isn't mechanically provided.

    If the PE is so good, the PE would have specified ducting materials/methods.

    If you install galvanized, it'll suck if the PE wanted stainless- wasted materials and labor.

    Around here, stainless is a SIGNIFICANT upcharge from galvanized. A 4" 26 ga galvanized 90* adjustable elbow is less than $5. A 4" adjustable 90* ell in 26/8 ga stainless is $30. A 5' length of 6" stainless snaplock pipe is ~$10 a foot.

    I can only imagine the $$$ of stainless 10" pipe and ells. Plus the stainless steel screws.
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