# seeking opinions on  exhaust extension for portable generator.



## St_Earl (May 24, 2015)

specifically, will this idea have a negative/harmful effect on the engine from possible back pressure issues?
205cc gas engine, stock exhaust is a 3/4" nipple pipe on a small muffler.

i want to attach a collar to the face of the muffler and attach flexible metal tubing ( 3 or 4 inch) to move the exhaust point away from the house. i want to be able to run the genny in my shed, but it's too close in my opinion. carbon monoxide could possibly seep up under the bottom edge of the siding into the house. and there are windows as well, and i want to be as safe as possible. i know cool air can get in through the electrical sockets, and we use child proof inserts in winter to prevent that.
i plan on just opening the shed doors a little and using sheet metal and strong magnets to close the gap,leaving only room for the pipe to run out. the genny would be front and center in the shed.
the prevailing winds come toward the shed doors, so i may need to run the exhaust around the left side of the shed. but i could also do a straighter diagonal run into the driveway and turn the end of the pipe back from the wind direction only at the end.

*how long a run is viable for this approach? does the massively larger diameter of the extension compared to the 3/4 inch exhaust help negate back pressure issues? what about bends?*

we don't get long outages here, and i really want avoid cutting a hole in the back wall of the shed.
and even if i did that, i'd need a rise to be above the snow line and at least two 90 degree bends.
so i'm not convinced that is actually a better way to go anyway.

i just don't want to damage the engine though.
thanks for reading and possibly sharing advice.  here's a pic of the location for reference -


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## Dr.Faustus (May 25, 2015)

i would think you would be okay, backpressure wise. because all the backpressure thats going to happen, happens before the exit point of the stock muffler. If you are attaching larger diameter tubing to the end of the stock muffler, it should be the same as venting to outside air. I cant comment as to whether or not this is actually a good idea. The shed is very close to the house for my liking. My friend 2 years ago ran his genny 10 feet from the house, and i guess his house had negative pressure and his CO detector started going off. 

I run mine in my detached garage, but that is far enough from the house, i have the generator exhaust sticking out the open back door of the garage and i have both car port doors open. This protects the gen from the rain. Its never set off my co detector either. If you do this make sure you have more than 1 co detector in the house.

personally i think the hole in the back of the shed is the way to go here. or up and out high on its back wall.


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## velvetfoot (May 25, 2015)

With all those garage doors open, it seems safe, but I've actually read of someone who went into a garage to tend a generator and didn't come out alive.


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## St_Earl (May 25, 2015)

thanks, guys. i think i'll be curling the pipe all the way around the left side of the shed and run it back even further than the back wall.
so really even farther from the house than if i ran a vent from inside the shed. 
if backpressure isn't an issue after the muffler, that clears my main concern 

like i said, we rarely get long outages, so i prefer not to start cutting into the shed.
i will still move the CO detector into the back bedroom if we end up needing to run the genny.


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## mustash29 (May 25, 2015)

CO is heavier than air.  In the absence of any air currents or wind stirring things up, CO will sink to the lowest spot it can find.

At work, our policies state we need 2000 CFM of ventillation for each welder inside a confined space.


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## firefighterjake (May 25, 2015)

mustash29 said:


> CO is heavier than air.  In the absence of any air currents or wind stirring things up, CO will sink to the lowest spot it can find.
> 
> At work, our policies state we need 2000 CFM of ventillation for each welder inside a confined space.



Are you sure about that . . . my own research in the past showed that CO was actually just slightly less dense than air and would tend to rise when warm to hot, but then would rather quickly fill out to all areas in a room . . . one of the reasons why most CO detectors and alarms are not required to be up high . . . or down low.


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## BrotherBart (May 25, 2015)

Yep. CO is slightly lighter than air and the old "heavier than air" thing is a widespread myth.

It rises and mixes quite handily with air.


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## Jags (May 26, 2015)

Pipe that genny out the back wall of that shed and fugitaboutit.  Use a larger diameter pipe than what feeds the muffler and the few feet that you are talking about won't make squat difference to that engine.  Leave the doors wide open during run time.


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## St_Earl (May 26, 2015)

i have gotten over my aversion to cutting a hole in the shed.
i have a 4" inch hole saw and will use 4"  flexible metal vent.

thanks to everyone for chiming in.
this will be a far less clumsy solution.


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