Replies

1. 
   Ted W. | Jan 28, 2009 10:26am | #1

   Is the vent meant for the attic space? If so, you may be doing more damage than good. Vent is there because the attic space needs it.

   As for flexible duct, I see it done a lot. You might want to check and see if it's allowed by code in your area. Not sure if it is here, just know I've seen it a lot.

   ~ Ted W ~

   Cheap Tools - BuildersTools.net
   See my work - TedsCarpentry.com

1. 
   Clewless1 | Jan 31, 2009 04:59am | #13

   uh Ted ... might read the post.

1. 
   Ted W. | Jan 31, 2009 07:01am | #17

   Uh Clewless1 ... I read the post. What are you seeing that I don't? ~ Ted W ~

   Cheap Tools - BuildersTools.netSee my work - TedsCarpentry.com

1. 
   Clewless1 | Jan 31, 2009 09:21am | #18

   He's venting a range hood, not an attic. May have missed your point in the way you stated it.

1. 
   Ted W. | Jan 31, 2009 10:53am | #19

   Understandable.

   The way he describes the situation, I get the impression he wants to hook the cook range vent to an existing attic vent, rather than installing a new one for the range. Needless to say, that's a big no-no. ~ Ted W ~

   Cheap Tools - BuildersTools.netSee my work - TedsCarpentry.com

2. 
   DanH | Jan 31, 2009 04:06pm | #21

   But exceedingly common.
   The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

2. 
   VTNorm | Jan 28, 2009 03:22pm | #2

   You can, but why not use one of the multi-adjustable elbows to get you there? The ridges in the flexible duct will be a magnet for catching grease and probably won't take kindly to being cleaned if you ever need to have the run cleaned out.

   -Norm

    

3. 
   MikeHennessy | Jan 28, 2009 03:25pm | #3

   I wouldn't. For range hoods, you want a duct that's as smooth and slick inside as possible to discourage build-up of exhaust "stuff" -- grease & the like. The flex duct provides too many nooks & crannys for gunk to latch on to and build up.

   Mike Hennessy
   Pittsburgh, PA

4. 
   barmil | Jan 30, 2009 06:50am | #4

   I used PVC for the ducting from my second story bath fan through the attic to the wall vent. The original fan failed to perform after ten years, and when I replaced it, the PVC was still smooth and clean inside. It also was insulated. I started with a remote Fantech near the vent, but now have a whisper quiet Panasonic that also has light for the bathroom during showers. Fantechs aren't as quiet as they claim to be. Its air rush noise was transmitted back to the bathroom, maybe because of the rigid PVC carrying it back. I don't know. But Panasonic makes a great bathroom fan, worth its cost, and it works well to keep shower moisture down. Even in subzero Wisconsin winters. I may seem to be digressing, but PVC does provide a smooth duct surface.

    

   
   

   ---

   Edited 1/29/2009 10:52 pm ET by BARMIL

1. 
   DanH | Jan 30, 2009 07:29am | #5

   But I'm guessing you weren't deep-frying fish in your bathroom.
   The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

1. 
   BillHartmann | Jan 31, 2009 03:52pm | #20

   No,, but the tub is often used to pickle herring..
   William the Geezer, the sequel to Billy the Kid - Shoe

2. 
   Piffin | Jan 30, 2009 08:08pm | #12

   I wouldn't use PVC for venting from a fire source 

    

   Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

5. 
   popawheelie | Jan 30, 2009 07:52am | #6

   One of the dangers of venting from on top of a cooking area is when the vent is on and there is a oil fire on the stove top.

   The fire form the stove top is sucked up the vent.

   So, you want to make sure if this happens that the fire is inside the vent duct.

   You could have a fire on the cook top and a fire in your dry, wood filled, hot attic real quick.

   I may be wrong, but when the vent is sucking up the fire throught the vent it can act like a turbo charger.

   The duct can get real hot real fast.

   So make sure it is done right.

1. 
   DanH | Jan 30, 2009 04:12pm | #7

   Interesting that you rarely hear of this scenario. You hear of dryer fires far more often. I don't know if it's because it doesn't happen or because it's just classified as a "kitchen fire".But the fan should be on a thermal fuse that will shut it off in the event of a fire.
   The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

1. 
   popawheelie | Jan 30, 2009 05:48pm | #9

   I didn't mean to sound alarmist. I wanted to let the poster know how important it is to get the ducting right.

   I was super/carpenter on one restraunt and there was a lot of attention put on the hood and ductwork. That is maybe why I attach so much importance to it.

   Part of the reason you might not hear about kitchen fires as much these days is the trend of cooking less in homes.

   This is just my opinion. But I think there is much less cooking in kitchens these days.

   Smaller families and both people working it makes sense to eat lighter.

1. 
   DanH | Jan 30, 2009 05:55pm | #10

   > This is just my opinion. But I think there is much less cooking in kitchens these days. So there ARE a lot of people who cook in the bathroom?? ;)
   The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

1. 
   popawheelie | Jan 30, 2009 06:11pm | #11

   Cooking in the bathroom? I've seen burn marks from that.

    

2. 
   Clewless1 | Jan 31, 2009 05:00am | #14

   But you still don't want a plastic duct, right Dan? By the time the fan goes off, you've had several seconds of REALLY HOT fire in the duct!

1. 
   DanH | Jan 31, 2009 05:15am | #16

   Yeah, it's probably not a good idea. But it would be fairly unusual for fire to get in there, unless the whole kitchen is already ablaze. The flames have to get through the filter first, and the filter is generally a metal mesh that will effectively stop flames. And by the time the flames have burned through the filter the fuse has probably been activated by the heat.The main hazard would be if someone stupidly operated the fan without the filter and THEN started a fire.
   The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

3. 
   BillHartmann | Jan 31, 2009 04:08pm | #22

   I could not find info on dryer fires, but they are not the major cause.From NFPA;"#
   84% of all civilian fire deaths resulted from home structure fires.
   #
   Cooking is the leading cause of home structure fires and home fire injuries.
   #
   Kitchens are the leading area of origin for home structure fires (40%) and civilian home fire injuries (36%).
   #
   Only 4% of home fires started in the living room, family room, or den; these fires caused 24% of home fire deaths.
   #
   8% of reported home fires started in the bedroom. These fires caused 24% of home fire deaths, 21% of home fire injuries, and 15% of the direct property damage.
   #
   Smoking is a leading cause of civilian home fire deaths."However, I doubt that the vent pipe rather has anything to do with making the fires bigger or smaller in a residential kitchen.As you said it would take a very large and long fire to get past the vent and steel mesh filter.A fire that big would also be rolling out under the hood and into the wood cabinets and in some case wood cover on the vent.Now restaurants are much different. They don't have anything flamable around the stove. And the cooking is much more intense and much more frying so that large amounts of grease accumulate in the ducts..
   William the Geezer, the sequel to Billy the Kid - Shoe

1. 
   DanH | Jan 31, 2009 04:19pm | #23

   Yeah, I'd agree with that analysis.
   The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

2. 
   DanH | Jan 31, 2009 04:29pm | #24

   And if you're really paranoid about home fires (and not a smoker) the thing to do would be to install a restaurant-style fire suppression system in the kitchen.
   The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

3. 
   VTNorm | Jan 31, 2009 04:31pm | #25

   From the USFA:

   *Clothes dryer fires account for about 15,600 structure fires, 15 deaths, and 400 injuries annually.

   *Eighty percent of clothes dryer fires in structures occur in residential buildings.

   *Annually, 12,700 clothes dryer fires occur in residential buildings resulting in 15 deaths and 300 injuries.

   *"Failure to clean" is the leading factor contributing to clothes dryer fires in residential buildings.

   *New home construction trends place clothes dryers and washing machines in more hazardous locations away from outside walls such as bedrooms, second-floor hallways, bathrooms, and kitchens.

   Lots more dryer fire info from these guys (and good products, too)

   http://www.dryerbox.com/reduces_fire_hazard.htm

   -Norm

1. 
   Clewless1 | Jan 31, 2009 05:36pm | #27

   *Eighty percent of clothes dryer fires in structures occur in residential buildings.

   Always kills me when the statistics spew forth w/ little perspective. Not picking on you or saying there isn't relevance in the material you presented. 80% of clothes dry fires occur in residential buildings ... where I'm guessing 80+ % of clothes drying occurs.

   80% of car accidents occur w/in 25 miles of your residence ... where 90+ % of your driving occurs.

   Statistics without perspective do little to really inform or educate us. They are often used in sales pitches to use true facts to distort reality enough to convince someone to buy something.     Sorry ... off on a tangent. The presentation of statistics reminded me of their dangers. Still good information, though.

2. 
   VTNorm | Jan 31, 2009 06:14pm | #28

   Link to the full FEMA report where the stats came from;

   http://www.dryerbox.com/news_articles/2007_us_fire_admin.pdf

   -Norm

    

3. 
   Clewless1 | Jan 31, 2009 06:34pm | #30

   No, I'm sure you didn't mis quote any stats. Stats are usually pretty factual in themselves. I wasn't questioning your data. Sorry.   I went off on a bit of a tangent ... talking about statistics presented out of context. Dr. Albert Bartlett hinted at this in his lecture on arithmetic and the environment. Without perspective we have no way of knowing what a statistic or numerical fact really means. I'm digressing again.  

   No offense intended to you or your material at all.

    

4. 
   BillHartmann | Jan 31, 2009 06:53pm | #31

   I looked at that, but could not find any place where it gave any hints about what percentage of home fires was caused by dryers..
   William the Geezer, the sequel to Billy the Kid - Shoe

5. 
   bmyyou | Jan 31, 2009 07:07pm | #32

   We checked with an appliance installer and he doesn't use flexible duct.  Thanks to all for the great feedback!

   Brian

6. 
   Dreamcatcher | Jan 30, 2009 05:18pm | #8

   I have seen metal flex duct used many times. Often in remodeling though, I have found them disconnected or ripped. The same with plastic flex duct. I assume the disconnected ones just shook themselves loose ( they are always disconnected at the top). I would assume you would replace flex duct before trying to clean it. It is also the quietest of the options. All the flex duct I've seen used though has been between 4 and 6 inch. When you say 7", I assume you mean 7" insulated flex duct as used for heating and cooling. Though I haven't ever seen it used for venting, it is a little bit smoother than the 4" stuff.

   Metal ducting is less common than PVC although more common in kitchens than in bathrooms. While I am not sure why this is, I do know that I had to replace one for a bathroom once that was leaking rust water all over the toilet. I assume it was because it wasn't insulated or air sealed well and water constantly condensed inside (it was also missing a flapper door on the exhaust). I replaced with PVC.

   PVC is the loudest material to use and most difficult to install. But, it is still reasonably priced, self insulated, the smoothest, and semi-self supporting.

   I wouldn't worry too much about fires, kitchen fires are rare. Laundry fires are much more common. It seems like some people live their lives in total fear of fires.

   DC

7. 
   Clewless1 | Jan 31, 2009 05:04am | #15

   No, No, and H__ no. Metal duct for range hoods. NO FLEX DUCT ... PARTICULARLY for this application!!!! I wouldn't do rigid PVC either. Use an adjustable elbow (metal) should do you just fine based on your description. Talk w/ the BO ... he will probably confirm that it's not code to do the flex or the PVC rigid (although I've been known to be wrong and known some BO to look the other way when you grease their palm).

   ABout the time you don't think you'll have a range hood fire ... you do and then you wish everything to be right.

8. 
   MSA1 | Jan 31, 2009 05:26pm | #26

   I was under the impression that range vents needed to be rigid.

    

   Family.....They're always there when they need you.

9. 
   Matt | Jan 31, 2009 06:26pm | #29

   Here, I rigid metal ducting is required by the mechanical code.  Your milage may vary.