Hot!Roof mount exhaust fan vs wall mount on sides of food truck

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DWags541
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/03/15 04:21:35


What do you call it when these louvered vent coverings have that deeper top than bottom thing going on? Seems like that would be best for keeping rain out. I am trying to search for these kinds of wall mounted vents but the best I can find is just a shallow metal ones.
Alternatively, there is this kind of design:

 
Minus the cylinder of course. But you get the idea. Angled covering to protect from elements and exhaust diverted downwards. I would think there would be less restricted flow in the first example up top. If I could be assured they would keep the water out in a variety of weather and transportation situations, I'd love to go with that.
 
If anyone has run across a source for these types of vent covers (The ones on the truck up top running in series), please let me know.

Could the tilt just be a normal vent with a custom fabricated duct to get the angle? 
edwmax
Double Chili Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/03/15 07:13:16
Those look like they were custom made by a sheet metal shop and are easy made.   The pictured louvers in the top pic are 'fixed' type.   I don't see an insect screen, which I believe would be needed too.    ... You can have a frame made then mount 'off-the-shelf' louvers in.
 
I think operable louvers would be better for your application.  When the fan is not running the louvers are closed keeping rain, birds & insects out.
Bistro a go-go
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/03/15 08:46:31
where are the closing louvered vents sold?? Prices? also MOST important, how are they cleaned of grease cause most cleaners will clean off expensive grafix in seconds OR do damage over short time,..? are the ones on movie trucks installed with some kind of grease filter other than the ones in the hood itself. we all know these hood filters dont trap all the grease, eh?
 
kingofcreams
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/03/15 09:47:38
I found and was going to use a single panel exaust louver from Grainger when my plan was to vent my hood out the side. Go to Graingers website and search for exaust shutters, wall shutters, exhaust louvers etc. You'll find some good stuff. The exhaust shutter I was going to use isn't angled but i've seen pics of these exact shutters in pics of other pro built food trucks.
DWags541



What do you call it when these louvered vent coverings have that deeper top than bottom thing going on? Seems like that would be best for keeping rain out. I am trying to search for these kinds of wall mounted vents but the best I can find is just a shallow metal ones.
Alternatively, there is this kind of design:


Minus the cylinder of course. But you get the idea. Angled covering to protect from elements and exhaust diverted downwards. I would think there would be less restricted flow in the first example up top. If I could be assured they would keep the water out in a variety of weather and transportation situations, I'd love to go with that.

If anyone has run across a source for these types of vent covers (The ones on the truck up top running in series), please let me know.

Could the tilt just be a normal vent with a custom fabricated duct to get the angle? 


kingofcreams
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/03/15 09:56:20
Check out Grainger and search for single panel wall exhaust shutter. A 10 1/2" x 10 1/2" is $33. The louvers shut automatically with no air pressure and open when there is. You would just either screw it directly to your rig or a frame you build and attach to your rig first then you could easily remove it to clean it. Since I am now going to roof mount my 12 volt fan I am thinking of going with a Broan Wall Cap. It has built in back flow prevention flapper and bird screen ( although I may add some smaller mesh screen for insects). THese are what is used on houses for your oven range exhaust and bathroom exhaust fans. Grainger has them but I also found them at Menards and are much cheaper there.
Bistro a go-go

where are the closing louvered vents sold?? Prices? also MOST important, how are they cleaned of grease cause most cleaners will clean off expensive grafix in seconds OR do damage over short time,..? are the ones on movie trucks installed with some kind of grease filter other than the ones in the hood itself. we all know these hood filters dont trap all the grease, eh?



edwmax
Double Chili Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/03/15 10:06:01
Bistro a go-go

where are the closing louvered vents sold?? Prices? also MOST important, how are they cleaned of grease cause most cleaners will clean off expensive grafix in seconds OR do damage over short time,..? are the ones on movie trucks installed with some kind of grease filter other than the ones in the hood itself. we all know these hood filters dont trap all the grease, eh?


 
WW Grainger    .... Mcmaster-Carr  ... any place that sells exhaust fans should have the louver, and/or sell fan & louver as a package.
 
For grease put a drip angle at the bottom of the louver to direct the grease away from the side of the trailer/truck; and, slope the duct work so the grease will flow back to the hood drip tray.     ... Also, the duct is required to be accessible for cleaning.  Most likely this can be done from the inside while cleaning the hood. If not the louver needs to be removed to clean the duct & louver.
post edited by edwmax - 2012/03/15 10:08:56
Bistro a go-go
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/03/15 12:58:03
i wonder what the big louver is covering below the angled ones?  thanks for the info. regards, mark
Bistro a go-go
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/03/15 12:58:03
i wonder what the big louver is covering below the angled ones?  thanks for the info. regards, mark
DWags541
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/03/15 18:49:22

What is a backdraft damper? Does it achieve the same thing as a shutter?
I am not sure of the terminology, but I wouldn't want the get something where the flaps open against the exhaust flow.
kingofcreams
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/03/16 09:06:23
I just got one of the then returned it. You would install it under a fan with the fan discharging out. When the fan is off it prevents outside air back drafting into the interior space. If I had a thicker ceiling I would have been able to use it. They make one for a wall and one for a ceiling / roof. Although the depth is only like an inch and a half once the damper opens its like 2 3/4" deep.
DWags541


What is a backdraft damper? Does it achieve the same thing as a shutter?
I am not sure of the terminology, but I wouldn't want the get something where the flaps open against the exhaust flow.


DWags541
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/03/18 02:32:40
kingofcreams

I just got one of the then returned it. You would install it under a fan with the fan discharging out. When the fan is off it prevents outside air back drafting into the interior space. If I had a thicker ceiling I would have been able to use it. They make one for a wall and one for a ceiling / roof. Although the depth is only like an inch and a half once the damper opens its like 2 3/4" deep.
DWags541


What is a backdraft damper? Does it achieve the same thing as a shutter?
I am not sure of the terminology, but I wouldn't want the get something where the flaps open against the exhaust flow.


 
Well, your description matches what I suspected it would be and a contender for what I will use. Do I understand you correctly in that you said you purchased a vent like this and returned it? If so, why? Is your ventilation on the side or roof?
Jackcon
Junior Burger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/03/28 16:45:10
kingofcreams

Check out Grainger and search for single panel wall exhaust shutter. A 10 1/2" x 10 1/2" is $33. The louvers shut automatically with no air pressure and open when there is. You would just either screw it directly to your rig or a frame you build and attach to your rig first then you could easily remove it to clean it. Since I am now going to roof mount my 12 volt fan I am thinking of going with a Broan Wall Cap. It has built in back flow prevention flapper and bird screen ( although I may add some smaller mesh screen for insects). THese are what is used on houses for your oven range exhaust and bathroom exhaust fans. Grainger has them but I also found them at Menards and are much cheaper there.
Bistro a go-go

where are the closing louvered vents sold?? Prices? also MOST important, how are they cleaned of grease cause most cleaners will clean off expensive grafix in seconds OR do damage over short time,..? are the ones on movie trucks installed with some kind of grease filter other than the ones in the hood itself. we all know these hood filters dont trap all the grease, eh?



 
What size of wire mesh and/or wire screen would you usually use in this situation?  I would imagine the mesh is going to be really fine if it can keep insects from getting inside of it?  Would you say like a 50 x 50 wire mesh would do the trick?  Or do you have to go even finer?
Infor on 50 mesh:
Dr of BBQ
Filet Mignon
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/03/28 17:51:26
Why would you have to put wire mesh on an exhaust system?
THE WILD DOG
Double Chili Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/03/28 18:14:12
bird and bug protection
 
Dr of BBQ
Filet Mignon
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/03/28 18:39:26
I have never had any bugs come thru my roof exhaust system and no birds LOL. Why are the side vents with flaps more likely to have those problems?
THE WILD DOG
Double Chili Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/03/28 19:04:31
if you have a roof mounted exhaust ( bell exhaust ) you should have a bug screen from the factory already installed,  The vent flaps are loose and they can and will flap open if the wind hits it the right way.  Plus it's a health dept thing. No openings bigger than 1/4 "
Dr of BBQ
Filet Mignon
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/03/28 19:09:43
Some health department rules are goofy and that's one of them. A fly will come in a 1/4 inch hole in a heartbeat. Or ants what ever.
OK just wondered but I'm not putting one (screen) on. Seems to be a great place to trap a lot of grease. I won't unless they press me on it. lol
edwmax
Double Chili Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/03/28 21:23:31
You normally don't need a bug screen on operable louvers (back-draft louver). Bug or birds are not going to fly in while the fan is running; and the louvers will not be open if the fan is off.   ... But open fixed-louvers would need bug screens.
kingofcreams
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/03/29 11:59:28
Yes I returned it to Grainger. Originally I was going to mount it on the side but then ended up mounting it on the roof. The Roof cap I endup up using has a built in flapper 
DWags541

kingofcreams

I just got one of the then returned it. You would install it under a fan with the fan discharging out. When the fan is off it prevents outside air back drafting into the interior space. If I had a thicker ceiling I would have been able to use it. They make one for a wall and one for a ceiling / roof. Although the depth is only like an inch and a half once the damper opens its like 2 3/4" deep.
DWags541


What is a backdraft damper? Does it achieve the same thing as a shutter?
I am not sure of the terminology, but I wouldn't want the get something where the flaps open against the exhaust flow.



Well, your description matches what I suspected it would be and a contender for what I will use. Do I understand you correctly in that you said you purchased a vent like this and returned it? If so, why? Is your ventilation on the side or roof?


Sapphirebistro
Junior Burger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/04/01 01:09:36
I'm really leaning towards back mount fan because of my hood and because I have a window all ready there .
PurpleCheetah
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/04/05 16:16:14
If I used this exhaust fan mounted on the side of my truck, could I use just 1 or would I need 2?
total btu's 215,000:
 
http://www.neobits.com/tp..._p1581594.html?atc=gbs
 
I would be mounting it inside my hood from hoodmart
Dr of BBQ
Filet Mignon
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/04/05 17:08:37
PC,
That is a neat looking unit, made by TPI but the add doesn't tell you the amount of cubic feet of air it will put out per minute. And that is what will tell you if it will remove your exhaust and or keep your trailer or truck cool in the hot months.
 
I called them (their number was on the page you linked) and this web site is just a retailer for lots of other companies, so this is not who you want to buy from. I also found out it moves 1600 FPM which is ok.
 
But again don't buy from someone that sells all kinds of junk and expect to get any service after you bought it. They don't even carry it in stock.
 
They would only tell me it was made by TPI and their site is
http://www.tpicorp.com/ you need to download the catalog and or call them and find out if they do internet sales or  who will be your cheapest retailer.
Now one more question why didn't you do all this research? It only took 15 minutes?????
PurpleCheetah
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/04/05 18:35:20
I did actually, I talk to prosupply ( another website that had the fan )and they gave me the phone number to TPI Corp who directed me to the catalog ( page 21-22) I looked at the catalog and found most info I needed ....however I can not find enough info on how to convert the BTU to CFM part. I did read this whole thread and got a round about figure as to the CFM from there so I could go off that I guess. http://www.prosupplyco.com/ceseries-3.aspx  has the fans for the cheapest I have found. TPI gave me phone numbers for retailer's close to me where I could go pick it up, but they are all closed for the day so I'll try tomorrow and check prices there.
 
I really do try to find things out on my own but sometimes I need another opinion ( or reassurance you could say) because I don't want to end up with another case of more than I need or wrong thing, or paying someone commission on a sale for selling me to much stuff that I didn't really need, or over thinking a simple situation........I guess I should just get two fans and at least have more than I need than less.
Dr of BBQ
Filet Mignon
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/04/05 19:58:58
"how to convert the BTU to CFM part"
 
Glad to hear you did your home work Congrats on that.
 
You can't convert BTUs to CFM, that's like converting ice to gallons per hour from a pump. But I need to know what your biggest concern is? Are you just trying to pull the grease and smoke out or are you looking to cool your trailer or both?
 
Write down your total BTUs, the sq footage of the unit, and fresh air intake= sq footage of the windows or doors that will remain open, but screened and call Ventilation Direct at the number listed on the top of this web page. Ask them what size fan you need for your operation. I think you'll find they are great to work with and have the cheapest prices in the country. I have dealt with them on 2 different units.
 
There site is
http://www.ventilationdir...gList.asp?cattypeid=39
 
They will do the math and calculate the proper exhaust fan you need and it will be correct and you'll stop worrying. LMAO.
jack
post edited by Dr of BBQ - 2012/04/05 20:42:45
PurpleCheetah
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/04/06 22:09:36
Thanks DoB I got in to late to call them today but I'll try Sat. or Monday...I am trying to do both Cool and degrease
Linairs
Junior Burger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/07/18 16:17:55
I've been trying to research the side wall venting configuration. Can't find anything. So has anyone done this right? I have a hood that came out of a restaurant. Can I use it or do I need a special hood made for wall exhaust?
Dr of BBQ
Filet Mignon
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/07/18 17:27:37
Linairs I've been trying to research the side wall venting configuration. Can't find anything. So has anyone done this right? I have a hood that came out of a restaurant. Can I use it or do I need a special hood made for wall exhaust?

 
Did you read this thread? It's full of imformation.
Dr of BBQ
Filet Mignon
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/07/18 19:24:58
Linairs
Junior Burger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/07/23 12:05:27
I did read this thread but what I got from it was a lot of questioning and what if's and such.  I was wondering if anyone has actually done it and was either happy or unhappy with how they did it.
I thank you for the links you sent me, but it still seems like no one is talking about a finished project.  Didn't know about Pacific Trucks.  That looks like a good place to start.
My son talked to Ventilation Direct and they pretty much say only the mushroom will do but I don't want that.  Our truck is tall enough as it is.  We do ice cream and may want a little cooking so I don't see the need for massive air flow.  Plus we have an air conditioner.  Sounds like we'd just be sucking out all our cold air.  Should we install a vent in the hood system to draw outside air in?  Saw some mention of an outside vent on one of the posts but don't really understand the system.  Haven't been able to find anyone local to help.
Dr of BBQ
Filet Mignon
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2012/07/23 15:12:50
Good questions and fair points.
 
In no particular order.
 
Most builds get done and the builder is busting his or her tail working after that and doesn't post much. Also most folks don't want to come on here and say "oh man I screwed the pooch on my build" and this and this is wrong.So we don't get a lot of after build reports.
 
I have only been around one system that had ("makeup air") out door air coming inside at the grill front so the system was sucking out the heat and grease from the grill and not the AC, or heat in the winter. It was in the dead of winter and colder than hell outside and as you reached across the grill to turn a burger from your wrist to your elbow was cold I mean frost bite cold. So in my mind they ("makeup air systems") work.
 
But that said they can get expensive to install, and you need to figure out how much air to bring into your hood area. The only way I know of to do that is get back on the phone with VD and ask them to tell you what system they recommend for your rig.
 
Tell them you also want to use a make up air system and ask what size pipe etc you need. They can figure it out in a heart beat. And yes they will want to talk mushroom type but you just need the CFM figure that they suggest you need and the CFM "makeup air" figure they suggest you need.Then when you build your system use VD's research, and make sure you get a total coming in and exhaust that matches.
 
I live in Illinois and we have about two weeks in early to mid August that are just miserable from the heat in a normal year. This year we have had several weeks already and the worst may be yet to come. I do not have AC in the trailer but run the exhaust fan all day to keep air moving thru the trailer. Again under normal conditions it's not bad with out AC.
 
good luck.
 
 
post edited by Dr of BBQ - 2012/07/23 15:15:00
cosmo64
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2013/02/28 14:19:08
Since I too am doing all the necessary research on a concession trailer build, I have been reading all of the related threads and taking notes. Does anyone care to post negative/positive results with their type of exhaust fan setups (vertical/horizontal with/without makeup air...etc)?
Dr of BBQ
Filet Mignon
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2013/02/28 15:02:38
To start with you need to keep in mind the overall height of your truck or trailer. And not just for highway use but for city driving as well. Most cities don't trim tree branches that hang out over streets and instead depend on semi trucks to clear low hanging branches. So semi drivers drive in the center lane when possible which means the curb lanes have lots of tree branches that will beat the heck out of your above exhaust fan housing and when it gets dented it loses some of it's designed swirl exhaust ability.
jack
cosmo64
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2013/03/01 20:59:32
Good points Dr of BBQ.
edwmax
Double Chili Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2013/03/02 05:33:07
Keep in mind what ever system/equipment installed, it will need cleaning to remove buildup of grease from the inside of duct & fan. Slope any duct work to drain into a grease collection can or to the outside.    ... Yes the ducts are very short in a truck ... usually.   So make any access needed easy so cleaning will not be a 'dreaded chore'.
daddywoofdawg
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2013/03/03 00:57:41
Someone on here not to long ago built a truck and we talked about where to get the fans like the food trucks used.I forget where he said. but search this forum and you'll find it.
cosmo64
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2013/03/12 15:46:58
Thanks edwmax, ease of upkeep is paramount.
DWags541
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2013/05/01 19:40:37


 
This is the system I am using for my exhaust at the back of my rig. The metal fan motor mounts have since been painted, and the fans wired up with their switches at the front of the rig.
The next step is the custom hood, which is being fabricated locally. These fans (12v) move plenty of air and I imagine I will only need them on low. I'll have a 3' propane griddle next to a propane steam table at the back.
 
I too was not interested in a vertical exhaust setup. Mostly because the fan systems are all AC power and I wanted 12v power for everything. But also because of the aesthetic of a huge fan on top of a moving truck. I did some research and saw some wall mount exhausts and that gave me the confidence to proceed with this custom job.
cosmo64
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2013/09/26 20:03:20
Are either of the fans adjacent to the cooking area/hood?
fishscale28
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2013/09/26 23:32:01
I opted to go with fans on the side of the truck vs the top as well.  I originally bought an amazing 14" fan (3 speeds up to 2100 cfm I think) but it was just a little too big so I had to end up going with 3 smaller 10" fans.  Still wish I could have found a way to go with the smaller as it is still more cfm than the three combined but se la vie....
hpx
Junior Burger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2013/09/27 13:42:33
I have a friend that runs a meatball truck out of Tampa. It is an older self built including his home made side vent exhaust. Right now he is grandfathered in with the hood he has but they are all over him to change out to a roof mount. Their reasoning is that a side mount pushes the grease out while the roof mount pulls it out and is more efficient and there for cleaner and less likely to accumulate grease.
fishscale28
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2013/09/28 01:57:54
Valid point but not a law, yet  As long as its the right motors and they're cleaned well and often then they're just as good, if not better, than their roof top counterparts.  I would never go the roof mount...just my .02 pesos...
 
RichardFla
Junior Burger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2013/12/01 00:06:15
I am not sure if this thread is still being followed but this is what I have been installing.
 
Low profile with a 16" total height ,1600 cfm and assembled with easily available parts.
I reinforce the curved front to deflect the tree branches.
 
The problem with roof mounted downdraft is the grease is deposited on the roof long term,side draft would need to be strong enough to "blow" the grease laden air away from the truck.
 
Well, I put a pic in but because I am new, no post. any other options?
 
post edited by RichardFla - 2013/12/01 00:08:36
kebamo
Junior Burger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2014/05/24 19:29:22
I got a 1975 cfm updraft fan and am going to install a control to slow it down so I just am pulling what I need to pull the smoke off the grill etc area. I am looking at a char grill and will have the power to pull more f needed Power is generator but have a new one and will,service,it each week oil change filter cleaning etc. plug once a,month. Use high quality synth oil (amsoil ) installed a 90degree angle pipe with gate valve for quick oil change. 6500 watts and will be pulling about 4800 watts at anytime. Also installed a 12 in 12volt electric rad fan push pull on generator to increase air flow across the unit to help with the heat. The reason I am using updraft is because I bought it real cheap on Craig's list 50.00. The owner thought it was bad because the fan woundnt spin fix the problem by removing the tennis ball that was causing it not to spin works fine 1/3 hp belt driven
BelCibo
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2014/05/27 21:28:16
A comment on the side mount fans.  I bought two 12" Fantech units for ours but have been having issues with heat.  Turns out the fan motors are rated to 40C and of course the hood air temp is much higher particularly above the fryer.  I have not been able to find a 60C 3.3 inch motor to swap it out with.  Still have not solved the problem even after replacing it with a new unit.  If someone has a 60C rated fan motor let me know what the p/n number is.  
fishscale28
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2014/05/28 12:51:23
See if you can find an industrial Totally Enclosed Air Over Motor (TEAO).  I only did a quick search and saw some options-they're usually made to deal with higher heat, etc. but are often much more expensive...
BelCibo
Cheeseburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2014/05/28 22:25:50
This is kicking my butt.  I'm looking for a 3.3" motor, 115vac, 1/30 or more hp, 1550rpm.  60C or higher ambient
post edited by BelCibo - 2014/05/28 23:17:19
Rcoy
Hamburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2014/05/28 23:05:59
This place has a ton of motors, perhaps a phone call or email would get you a lead.
www.emotorstore.com
Inkys
Hamburger
Re:Roof mount exhaust fan vs wall mount on sides of food truck 2014/08/21 14:16:15
Its been a while, but I've currently been dealing with the same issue, so I'll add my 2cents for the next guy that comes along.
 
Lets step back for a moment from personal preferences;  Both 12v auto fans and fancy centrifugal fan upblast units can be used. Neither is "Right" or "Wrong", both have their pros and cons.
 
A local fabricator that has been making food trucks in my area for 20 years has always used 12v motor side exit fan hoods and they still do today. They make their own hood and exhaust system and produce 1 -4  truck per month. Their trucks are all over northern California (is this what some have called a west coast truck ??).  They don't release design info, but their motors look like 12v sealed auto fans.
 
12v auto fans
------------------
These need to be sealed motors to protect from grease n moisture.
Yes, they take more maintenance. If not cared for you'll be replacing them every 18-24 months. But they only cost about $50. With some searching you might get them for less. With some grease tight automotive wire  connectors, you could swap them out in 15minutes.
 
Upblast fans on the other hand, cost from $600 - $1000
 
So here is a basic list or pros and cons
 
12v Auto fan side exit
-----------------------------
Pros
 + Lower cost
 + lower power use (this is a biggie for me)
 + often variable speed and wire separately if you don't always want all fans running (See note)
 + Cleaner/Lower profile (exterior exit)
 
Cons
 - Seemed to be hard to find with fan. figuring our cfm between different blades and motors is a real pain.
 - More maintenance/grease on exterior. Need to clean often or you'll have black grease stains at the exit.
 - periodic replacement
 
 
If you want to go 12v, the fixed lift out louvers act as a second set of grease filters and are easy to clean (I suppose you could rout a drip line at the bottom to capture the drip, but I haven't seen one)
The flapping type louvers seem like more trouble to clean.
 
Upblast fans
----------------------
Pros
 + Will definitely handle the job
 + Less maint/cleaner exterior - Captures n directs more grease
 + Last a long time
 
Cons
 - More expensive
 - Ugly "barrel" on roof
 - Height clearance issues - Just wait until you pull away from a curb location having forgotten there is a low tree branch nearby!
 
Codes don't yet require upblast any where I know of, but most ventilation firms will strongly encourage you to go that way. In part this is because it does work. In part it's because THAT"S WHAT THEY MAKE AND SELL! The side exit 12v systems are what a lot of fabricators have done for years. It's less expensive in money and power use, but takes more maintenance.
 
I personally don't like the look of upblasts, but I do like how effective and maint free they are. But the big issue for me is power.
 
Note about 12v side exit: Just my sense, but i think if you only turn on some of your fans, you'll draw air in from the other fans reducing effective draw from cooking equipment. A back draft damper might solve this as well as any issues if you're in a high wind area.
 
Downdrafts
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From what I've been told, these are not "grease rated" ... i.e either don't route/trap the grease. or motors are not protected from grease flow.
 
Questions
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1. If any one has a good source for 12v fans (especially with cfm and amps/wattage info), I think a lot of people could use it.
2. RichardFla  mentioned a 16in upblast unit. I'd like to know where he saw that. The lowest I've found is 22inches
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