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Posted: Mar 05, 2007 07:20 PM
Generator roof exhaust
I have a diesel generator that I routed the exhaust through the floor. I would like to change it to exhaust through the roof. What did you guys who built your own rigs use as a flange and seal on the roof? I have a 2 1/8" exhaust pipe so most HVAC exhaust flanges are too small. Pictures would be helpful!

Thanks, Tim
Granite State Spray Foam Co.
Posted: Mar 05, 2007 07:54 PM
I haven't done it yet but would most likely cut a hole about 12'x12' in the roof. Build a curb using metal approx 6 to 8 inches high on the roof and flash it in with SPF. Then I would fab a cone base using 22 or 24 gauge galv that extends down the sides of the curb 2 or 3 inches (to make water tight), and put a collar at the top of the cone base. You could use metal strapping around the pipe itself and screw to the cieling joists of your trailer.
I have my hose on top of my trailer, and built a curb similar to what I have described above, which has a removable top so the gun side of the hose can be run back into the trailer when not in use.
Posted: Mar 05, 2007 08:02 PM
You could also cut a hole in the metal curb cap that is the same size as the exhaust pipe, and attach the curb cap to the curb. This should keep the strain off of the cone, and eliminate the need to use strapping below. Then solder the cone to the curb cap and put the collar.
If you do it this way, send me a picture....
Posted: Mar 05, 2007 08:41 PM
Wow, I was just saying that I was going to change my next rig to exhaust out the floor.
I don't like the possibility of rain getting down the pipe even tho I have a cap on it. Also, the pipe could burn people going up, less apt to going down I think.

Why do you want to do the opposite? What do you identify as the down side of thru the floor?
Posted: Mar 05, 2007 08:49 PM
Well, I have a non EPA approved generator (shhh don't tell anyone). That smokes a bit. I was hoping to get the exhaust 8 feet up in the air and away from the spray rig. If I can tune my generator and get the fuel adjusted correctly then I may be able to leave it through the floor. It certainly is a better setup in my opinion.

Granite State Spray Foam Co.

Oh and if i read thunderbay's post correctly, he recommends a 12 FOOT by 12 FOOT hole in the roof???? HEHE

Posted: Mar 05, 2007 09:39 PM
No, a 12 inch by 12inch.
Posted: Mar 05, 2007 09:40 PM
do you know what a curb is?
Posted: Mar 05, 2007 09:40 PM
or not...
Posted: Mar 05, 2007 09:44 PM
I was just kidding about the hole size. My trailer is only 8 feet wide so I knew it was a mistake!

Thank you for your helpful info. Not sure if I am going to go through the roof yet.

Granite State Spray Foam Co.
Posted: Mar 05, 2007 09:47 PM
You can buy a hi temp. boot to run your pipe thru and seal it to the roof. They come in a couple of sizes and you cut to fit. The rubber seals against the pipe tightly to avoid leaks. I used one to seal a 12" chimmney going thru my shop roof and have never had a problem with it. Skip
Posted: Mar 05, 2007 09:56 PM
Skip, are those the same as you buy for residential roofing (thinking stink pipe flashing) or are they different? I haven't been able to locate one at my local home center. Also those are usually made for a pitched roof, the roof on my trailer is essentially flat.

Granite State Spray Foam Co.
Posted: Mar 05, 2007 10:19 PM
Please accept my appology Tim at Granite Slate.
Posted: Mar 06, 2007 11:13 PM
They are basically the same except for the hi-temp rating ( not sure if it would be high enough though). They also make them for flat roofs. You may need to get one from specialty place or roofing supply place. I think we may have bought them from Fastenal in the past. I think they have a website. I'll check around for you when I get a minute. Skip
Gerry Wagoner
Posted: Mar 07, 2007 07:23 AM
We had our exhaust routed through the floor at first, then changed to the roof. Works well. I manufactured a concentric flashing flange with galvanized double wall exhaust couplings. I filled the space between them with high-temp silicone. This acted as a shock asborber and a seal. I purchased a stainless steel tube from MSC and ran that out through the roof and put a flapper on it. Works great.

Might try a side exhaust on our next rig we are building.

Todd Baxter
Posted: Mar 07, 2007 07:28 AM
you can do this a few ways, get a lead pipe boot and the problem is solved. also use an hvac flashing for a water heater.
Posted: Mar 07, 2007 08:36 AM

I looked at those HVAC flashing kits, but the smallest I could find was 3". My exhaust pipe is around 2". I should try a plumbing supply store.

I will look for a lead pipe boot as well.

Thanks for all the info guys!

Granite State Spray Foam Co.
Michael Flander
Posted: Mar 08, 2007 05:05 PM
We offer an exhaust assembly that will work for you. You will need to cut a 4" hole in the ceiling. It will not allow rain into the trailer and will work with your 3" pipe (This assembly will couple to it actually).

Give me a call for more info.

Mike Flander - Endisys
763-428-5075 ext. 205

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