What to make generator exhaust stack out of?

[Christyhicks]

When we were starting the conversion of BigBus, I insisted that Larry figure out a way to exhaust the generator through the roof. 

Of the generator, he used a flexible exhaust hose, used a union to tie it to the stack, then extended exhaust pipe on up through the floor and roof.  We used a 4" double wall flue pipe (hvac people of course) as a "chase".  At the floor, we mounted a double wall flue pipe collar on the bottom and on the top side of the floor, extending the flue pipe on down through the floor about an 1" below floor level.  This gave us a "thimble" of sorts to keep the floor from getting hot. 

We ran the flue pipe on up and terminated it just flush with the top sheetmetal on the roof.  We used homemade "keepers" to keep the generator exhaust pipe centered in that chase.  The exhaust pipe continued on up through the center of the chase and terminated about 8" or so above the roof.  So, if you're picturing this, you'd see that we have free airflow from the generator compartment, around that exhaust pipe, all the way up and through the roof.

The last thing was to figure out a way to keep rain from coming back down the pipe.  Larry built a flashing out of a flat piece of aluminum, with a hole cut in the center, and riveted a tubular shaped piece (with bendable tabs cut in the bottom to insert down through the hold of the flashing and bend back underneath it) to that flashing, then sealed the seam.  This sealed the hole in the roof, and now we've got a small round tube sticking up, with a smaller exhaust pipe sticking through it.  All we needed then was a cap.

Again, we had to fabricate it, so he bought two curved tips and welded the small one to the exhaust pipe, and used a larger one, cutting tabe and bending them in to meet the smaller one, fashing a rounded top basically to come up against the center one.  It's hard to explain, but he ended up with a stepped cap. . .  maybe 3" or so on the wider portion, curving down and attached to a 1 1/2" center one.  . .  welded to the exhaust pipe sticking up.  The wider 3" portion slid down over the flashing sticking up through the roof so that the flashing was sticking up between the outer portion of that cap and the inner exhaust pipe.  Once we slid it down, we supported the exhaust stack at the bottom so that the cap did not touch the roof and there was just a little gap between the top of the flashing and the inside rounded portion of the cap.  Does this make any sense?

[TomC]

I too have a transit (AMGeneral 10240B).  I installed a 10kw Powertech Diesel generator next to the front seat like a front engine-facing backwards so the lower part of the gen is tucked under the dash.  The reason- I have 3 roof top A/C's for my only A/C system.  With 2.25" of sprayed insulation, two A/C's running while driving in 108 degree weather (hottest I've been in) will keep the interior at a comfortable 75 degrees.  Turn all three on and my wife puts on a sweater. Also, the only propane I have (I really dislike propane) is the stove and furnace.  So with mostly all electrical including two 10gal water heaters, electric heat in the bathroom, 2500 watt inverter with two 8D's, a 6.3 cu Norcold AC/DC refer and a Norcold AC/DC 2.1 cu chest freezer, microwave, toaster oven, washer/dryer, I can truly use the 10kw of the generator.
Personally, I don't quite see how you're going to get along with a measly 1kw worth of electricity-unless everything is propane and your only electric A/C is that small 5,000btu window unit.  How do you stay cool in summertime?  Still have the over the road A/C?  Good Luck, TomC

[cody]

I guess the question I would have is would the run affect the operation or longevity of the generator, we have to realize here that the generator in question would pretty much fit in a bread box and has an exhaust slightly larger than the diameter if a pencil.  The honda 1000 is very small in size.  When you feed the puff, puff of that small an engine into that size of a pipe and run it that far what is the long term and would it be detrimental, my initial gut feeling is that it may hurt the generator, the dealer supports that idea and says the warrenty would be voided, I'm sure an alternate method could be worked out, I understand that the cost of the generator isn't huge at less than a grand but to someone like me a grand is a lot right now. This isn't a 10 or 15 HP diesel generator were talking about, this one is easily picked up and carried around with one hand.

[Van]

Right, it's not a big gen set, so why all the fuss in trying to make it quieter? Ours is a 5.5 onan)(CCK type) and that thing will wake the dead, of course with nothing but the header pipe . Yesterday I picked up a 10 foot section of EMT( 7 bucs @ true value) a 90 elbow ( 3 bucs ) and some couplers and we are all set to be nice neghbors . Spent a total of 25 dollars and this will do the job nicely, if not I can always turn up the tunes to drown out the generator LOL!

[cody]

Van, that idea ia brilliant, our generator is a 3000 watt honda, extremely quiet but we also carry a DJ system with 10,000 watts of raw power, if we were to crank that with an 8 hour load of rap or hiphop, I'd be willing to bet nobody would complain about the generator sound lol.

[Van]

Just took these

[Christyhicks]

Oh gosh, I guess I should pay more attention.  I thought you were talking about a big genny. . . ignore me please. . . (it's not hard, people do it all the time, ha ha.).  Christy

[Van]

Alright Cody ! You bring that stuff, and I will most certainly park next to you guys LOL

[gus]

After over 50 yrs of using conduit pipe now I find out it is EMT and I didn't even know it all this time!!

[Busted Knuckle]

And all this time I thought EMT stood for Emergency Medical Technician! 
  BK 

[gus]

Me too!!