Exhaust options for my 4’ x 4’ generator shed

[mgstevens]

I have a similar setup (see pics): 9K generator, 3.5' x 5' x 4' custom enclosure, wood-frame/plywood-clad, with cross-ventilation intake and louvered exhaust fan for heat. For the engine exhaust, I was able to get a piece of 2.5" exhaust pipe bent and flared to go over the exhaust exit on the engine (no mods!) and have been running it for 3 years. Ran it earlier today for a few hours during a planned outage.

From the outset, the heat generated by the engine and generator was too much for the fan - the temp-cutoff stopped it. Any 2 of the three doors (flip lid/roof and one of two barn doors) open during operation is enough to keep it in operating temp range. I was going to try to insulate the enclosure to cut noise, but once the operating configuration was determined, there was no point. Fortunately, the non-open part of the enclosure faces the house so a fair bit of clatter is cut away. Up to 10-15db.

For the engine exhaust, the flared pipe is plenty for the smaller engine exhaust to expand into. To deal with the pipe passing through the wood structure, I made the passage hole in the wood siding larger than the pipe and lined both inside and out with cement-board panels, cut tight around the pipe. The unit has run like this for almost 40 hours with no ill effect to the wooden materials near the exhaust pipe. The thing sounds kinda throaty (think baby Harley..) and I will be addressing some of that with a small rock pit for the exhaust to push into for some sound reflection breakup.

I think any small enclosure will be a problem to vent enough to keep cool while closed-in.

 

[Jac65]

If you are going to use a fan, make it an intake fan that draws in fresh air and blows it across the generator. Route the engine exhaust outside and let the vents expel the higher pressure hot air from around the generator.

 

[redman135]

I had a water pump setup similar to your genset.
I used a straight pipe for the exhaust(6' x 13/4" approx) through a corrugated iron wall. The roof was 10 - 12" above the top plate on one wall and sitting on the top plate on the opposite , and the gap left open for ventilation.
Shed size was 8l x 4w x 7h, and the exhaust exited on the lee side of the shed to avoid heating incoming cooling air.

I would suggest you mount a radiator directly into the (windy side) wall and make the whole lee side wall a permanant louve type for cooling.
Generators make a LOT of heat, far more than most people releaise.

 

[DaBear3428]

Thanks, grs - will use double-walled stove pipe. I looked over the generator again, and it turns out that the exhaust is only about 2 inches across. so, putting it in front of a 6 inch stove pipe should be sufficient. And I do not plan to use an exhaust fan after all. Just six dryer vents up near the top of the gable ends.

you probably know this but the exhaust should be sealed from the engine to the exterior and run to a point that it cannot be sucked back inside the shed (unless you want to use the shed to euthanize some stray animals). running the exhaust pipe to above the roof line a few inches works, you can check your local building codes for cheminies. as to cooling air most generators list the cooling air required to properly cool the engine and alternator, i would look that up and then provide a low cold air inlet / high exhaust with fan setup to match the airflow required. I have lost some friends to portable generators in the past.

 

[barts]

Pulling 6KW from your generator will take about 1 gallon/hr of gasoline... which is 120K BTU. The 6KW for a hour is roughly 20K BTU, and that's the only part that escapes the shed. Everything else goes into heating the exhaust, cooling air, generator, engine, etc.

So you're dumping about 100K BTU/hr into your shed - a good size home furnace worth. Figure 2x that if you're running hard. Lots of air circulation is a good idea; the "just a roof" plan will definitely work. If you need to keep small animals out, consider wire fencing; hog fencing if your problems are with 2 legged ones.

 

[71bronco]

Why not just have a roof over it with no walls. Make it a little oversized to keep rain and snow off.

Jeff

 

[Egon]

If you want four walls shroud the engine so the cooling fan brings in outside air that gets exhausted outside. For the exhaust use flexible metal exhaust pipe with a proper wall fitting. Run the exhaust pipe into two 45 barrels connected via the large bungs and make a larger hole in the last barrel for exit gasses. Keep the exhaust on the same side as the engine shroud exhaust.
If necessary add a bathroom fan blowing air into the engine shroud.

 

[check]

Got a length of double-wall stove pipe, and it is sitting right on the exhaust pipe. Will attach it with a couple of L brackets, and put some more vents in at the other end.

 

[MadJack]

14 years off grid here...
my 5 x 8 genny shed has 6' walls, and is open between the rafters. I thought the same a you, tried the exhaust extension but shitcanned the idea. Even with flex pipe it was a pain to keep aligned.
I just found a scrap piece of expanded metal ( 16x20") and cut a square hole low on one wall, then screwed the expanded in. Air in the shed does get fairly warm but nothing that will bother a portable genny.

I not have a generac eco-gen 6000w propane standby for aux-power during rainy/storm weeks. Mounted that on an old seadoo trailer so I don't have to pay extra for a service call when I want technical maintenance done.

(I still keep and run the portable 'back up' in the same shed just in case)