Generator Exhaust Through Roof?

[slowmachine]

As I work through the redesign of my gutted MH, I am considering re-routing the generator exhaust through the interior of the coach to terminate above the roof. I see advertisements for Newell and Prevost-based MHs that have this feature from the factory, so I am sure that it can be done safely.

At least some (maybe all) of these high-end MHs have the generator mounted in a mid-coach basement bay. My Cummins/Onan HDKAJ QD7500 is mounted in the front of the coach, and I doubt that relocating it to one of the basement bays, farther to the rear, would be practical or worthwhile.
The manual provides no limitation for exhaust pipe length, but does specify that the back pressure under full load must not exceed 2 inches water column within 6 inches of the muffler outlet flange.

The exhaust run would have to be long, 30+ feet, with two 90-degree bends and at least two of lesser angles. It is a fairly simple task to assemble a test exhaust system to verify that I can stay below the back pressure limit, but I find no information for exhaust components (wall/floor thimbles, insulated pipe, etc.) for smaller pipe diameters than residential gas vent or chimney applications.

If anyone has knowledge of the design and construction of the pipe section that passes through the coach interior, I would appreciate any information that you can provide.

FWIW, I already have a Genturi. I would like to eliminate it.

[followingsea]

Originally Posted by slowmachine

I see advertisements for Newell and Prevost-based MHs that have this feature from the factory, so I am sure that it can be done safely.
.

I am sure it can be done safely but can you do it safely?

As an engineer I hate change. If it isn't broke don't fix it.

In other words you should have a very good reason to change something. Marketing documents are trying to sell something more expensive by conning you into thinking it is better.

Do know what the KISS principle is?

There is currently a CO poisoning epidemic thanks to cheap portable generators.

[n2587n]

yes you can do that .
the pipe from the gen is small like 1.25 " just point that up in to a larger pipe like 2.5" dont seal the small pipe to the large pipe , the hot exhaust will make a up draft and suck in lots of cool air . that will keep the pipe cool and reduce the potency of the exhaust when if comes out

look at this on amazon . you could design yours based on this

Camco Gen-Turi RV Generator Exhaust Venting System, Reduce Generator Fumes And Noise, Easy To Install And Disconnect (44461)

[Hit_the_Rhod]

Personally I would be very leery of running an exhaust through a habitable area (anywhere enclosed by your outer walls) because of the potentially fatal consequences of CO poisoning if there were to be the slightest leak, even years down the road. Many RV generators are mounted on slides for ease of maintenance/repair, that would also complicate the equation. I too have a genturi, but have yet to use it except testing. Good luck with whatever you decide!

[cinitall]

Take a look at some Prevost converter websites, they are running the exhaust through the roof but it eats up some rear bedroom space.

[BrianGlenn]

Originally Posted by followingsea

I am sure it can be done safely but can you do it safely?



As an engineer I hate change. If it isn't broke don't fix it.



In other words you should have a very good reason to change something. Marketing documents are trying to sell something more expensive by conning you into thinking it is better.



Do know what the KISS principle is?

Lol. I too am an engineer but I am always trying to change things - by making them better. And yes KISS principle is good advice.

Are there smaller B-vent pipes in the gas fitting world? I wonder what RIVA code states for venting fired devices? Curious, and maybe someone with a Prevost, Bluebird, or Newell may chime in on this thread.

Brian

[Brentw]

Interesting, I'm picturing a floor to ceiling chimney chase against an outside wall where it could be vented top and bottom (like your fridge compartment). Can't say that I have ever heard of thimbles or a clearances to flammable material for an exhaust pipe.
A well constructed and vented chase should alleviate concerns about minor Co leaks, but now it would have to be insulated.
Some change to be sure.

[hohenwald48]

Originally Posted by Hit_the_Rhod

Personally I would be very leery of running an exhaust through a habitable area (anywhere enclosed by your outer walls) because of the potentially fatal consequences of CO poisoning if there were to be the slightest leak, even years down the road.

I wouldn't let it worry me too much assuming it is done properly. Just about every gas water heater and furnace installed in regular houses do exactly the same thing. ie: vent the exhaust through a habitable area.


Another consideration would be roof vents (the opening kind) anywhere in the area. If one is open and any kind of exhaust fan (bathroom, kitchen) is operating it could pull generator exhaust into the motorhome.

[slowmachine]

I snagged this Newell photo from an internet search. You can see the exhaust protruding from the roof at mid-coach. I think it is ugly, but still a useful example.

[windsorbill]

I'm following this thread.

Is your genny up front on a slide out tray? If so, the exhaust system is going to have to be quite flexible, maybe some sort of hose.

[slowmachine]

My generator is not on a slide-out tray, though I would like it to be. As often as it would need to slide out, I don’t think that disconnecting the exhaust would be too much work.

[spsm]

I know what my Kiss principle is. So what is yours ?

[Superburban]

I would get a 2&1/2" or so by 10 feet single piece of exhaust pipe, and mount it through the floor, and roof, with no joints. Then run the smaller gen exhaust inside that.


Maybe even run the first exhaust pipe inside a 3" or so PCV pipe, for some added insulation, and sound deadening.

[followingsea]

Originally Posted by BrianGlenn

Lol. I too am an engineer but I am always trying to change things - by making them better.
Brian

Better how? By making it more expensive, less reliable, and more dangerous.

I have lots of example of well meaning engineers doing just that.