# Kitchen Range Exhaust - distance from combustibles



## rossn (Mar 7, 2021)

Hello,

Hopefully this is posted to the right place.

I'm running a 10" sheet metal duct out the roof, for an island range hood.

*Is any separation of the residential kitchen range hood exhaust duct required from combustible materials?* I believe part of the reason flex ducting is not used, is due to potential fire hazard with the range hood, so just want to verify that as I go through the roof I don't have minimum separation requirements from combustibles.

Additionally, do I understand screws are allowed in this duct, and minimum of 3, evenly spaced?

Lastly, the duct slides up into the roof cap (about 3"). Is any sealing or attachment required there? Both would be near impossible, though possibly from the inside for both.

Many thanks!


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## Paul Sweet (Mar 8, 2021)

IRC M1503 requires kitchen cooking exhaust ducts to have a smooth interior surface (no flex duct or screws).  Pop rivets might be OK.

I don't see a requirement for separation from combustibles.  It would be good to avoid direct contact between the duct and wood framing.


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## Teeshot (Mar 8, 2021)

In CA, it is considered as Environmental Air and has no requirements for separation to combustibles.


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## rossn (Mar 8, 2021)

I'm not seeing anything in IRC M1503 against screws, only smooth ducting (which I don't think suggests no screws). Do you see it on another cycle? Conceptually, I don't think there is the same risk as with a clothing dryer, where they see it as a possible catch and build surface. I do see screws explicitly prohibited for dryers in M1502.4.2.


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## Inspector Gift (Mar 8, 2021)

3 Questions.   1 Comment.

1. Gas or electric cooktop?
2. What does the manufacturer's listing require?
3. What is the adopted code in your jurisdiction?

The code sections for Range Hoods (M1503.1) and ducts serving range hoods (M1503.2) do not prohibit screws.   
"Screws or similar fasteners that protrude into the inside of the duct" are only prohibited in Dryer ducts. (M1502.4.2)


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## rossn (Mar 8, 2021)

Inspector Gift said:


> 3 Questions.   1 Comment.
> 
> 1. Gas or electric cooktop?
> 2. What does the manufacturer's listing require?
> ...


Thanks. We are on 2015 IRC. Gas range, but no idea the model yet. This is a rough-in for the first phase of the model, while the ceiling is torn out and the roof is being replaced


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## rossn (Mar 8, 2021)

rossn said:


> Thanks. We are on 2015 IRC. Gas range, but no idea the model yet. This is a rough-in for the first phase of the model, while the ceiling is torn out and the roof is being replaced



I should clarify, range would be dual-fuel, and the model isn't known yet. The vent hood is selected, and there is no requirement, other than ridgid metal duct and this: "Fasten all connections with sheet metal screws and tape all joints with certified Aluminum Tape or Duct Tape."

Does a manufacturer mean that mean I can't use UL rated duct mastic? I can't imagine an inspector would be concerned with that.


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## rossn (Mar 8, 2021)

And I did find this "Installation work and electrical wiring must be done by qualified person(s) in accordance with all applicable codes and standards. Including fire-rated construction."

'Including fire-rated construction'... I assume that means any related residential kitchen exhaust hood requirement called out in IRC. Thoughts?


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## Inspector Gift (Mar 8, 2021)

rossn said:


> I should clarify, range would be dual-fuel, and the model isn't known yet. The vent hood is selected, and there is no requirement, other than ridgid metal duct and this: "Fasten all connections with sheet metal screws and tape all joints with certified Aluminum Tape or Duct Tape."
> 
> Does a manufacturer mean that mean I can't use UL rated duct mastic? I can't imagine an inspector would be concerned with that.


Rossn,
The Residential Code is silent regarding the taping of the joints in residential kitchen hood exhaust ducts.  But if you are concerned, look at the listing on the tape or mastic sealant and see if it is not approved for residential kitchen hoods.   I doubt that your inspector will notice or care.    The duct material should be 28 gauge galvanized steel, stainless steel, or copper.  And no thinner than 28 gauge.


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## ADAguy (Mar 29, 2021)

Given that many residential kitchens are using commercial ranges with high BTU  burners, the exhaust duct should be a min. of 1" clear from combustables.
Restaurants require either ductwrap above ceilings or 5/8" type "X" shafts to the roof.


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## Teeshot (Mar 29, 2021)

ADAguy said:


> Given that many residential kitchens are using commercial ranges with high BTU  burners, the exhaust duct should be a min. of 1" clear from combustables.
> Restaurants require either ductwrap above ceilings or 5/8" type "X" shafts to the roof


 "This appliance is intended for commercial installation only and is not intended for home use." This is a reference for a commercial range that was copied from a Wolf spec. sheet. Commercial ranges are not typically listed for residential use so the clearance to combustibles should be a non-issue.


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## klarenbeek (Mar 29, 2021)

ADAguy said:


> Given that many residential kitchens are using commercial ranges with high BTU  burners, the exhaust duct should be a min. of 1" clear from combustables.
> Restaurants require either ductwrap above ceilings or 5/8" type "X" shafts to the roof.


If its truly a commercial range listed for commercial use only, it can't be installed in a residence.  There are "commercial style" ranges listed for residential use, but they are still smaller than a commercial range and have all the safeties of standard residential ranges. 

A true commercial range can only be installed in a commercial application.  They are typically over 200,000 BTUs (compared to 60-80K for even the largest residential ranges), require clearance to combustibles for the range itself (no cabinet insulation), and often have standing pilots without safeties on them.  Because its a range intended to be installed in commercial applications only, I would interpret that to mean it needs a commercial (full Type I) hood over it as required by the IMC.  Local fire department was a little miffed at me when they wanted to put a commercial range under a residential hood in a new firehouse and I told them to switch to either a residential range or a Type I hood.


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