This is a Suncast plastic shed which I have turned into a generator shed/quiet box. I first added air inlets and a fan outlet. Next, I added a flexible metal exhaust pipe to get the hot exhaust out of the shed. I have added Rockwool (ComfortBoard 80) insulation to the walls, Kilmat sounddeadening vinyl to the lid, side baffles for the air inlet/outlet to absorb and redirect the sound, and finally my FrankenMuffler to the exhaust pipe. The FrankenMuffler is a 20 gallon galvanized trash can that has a perforated pipe running down the middle and an outlet on the bottom. The rest of the can is filled with mineral wool insulation, which is excellent at sound absorption and is fireproof to over 2000 degrees F. The exhaust shouldn’t get above a couple hundred degrees. As you can see in the video, this muffler did an Excellent job of deadening the sound! While the rest of the ideas for the shed were dug up from other videos and forums, I haven’t seen anyone take this approach to quieting a generator exhaust yet.

** UPDATE: JUST ADDED:
DIY Generator muffler build Version 1.0 The FrankenMuffler Lives!:
   • DIY Generator Muffler Build (Version ...  

NEW!: DIY Generator muffler build Version 2.0 The Bride of FrankenMuffler:
   • DIY Generator Muffler Build (Version ...  

Links to earlier sound tests for the shed (below)
Generator Shed Sound Test #1 (No Sound Insulation):    • Generator Shed Sound Test #1  (No So...  

Generator Shed Sound Test #2 (Sound Insulation Installed, Side Baffles, but no muffler):    • Generator Shed Sound Test #2  (Sound...  

Generator Shed Sound Test #3 (Full sound insulation, side baffles, and muffler):    • Generator Shed Sound Test #3  (Full ...  

Disclaimer: This video simply shows what I built, and it is intended to provide a few ideas when building your own shed or muffler. I am NOT an expert builder or designer, so take my advice with a grain of salt, and use common sense in your build.

WARNING: Do NOT build your generator shed near a window or door to your house! CO/CO2 can be deadly, and you do NOT want it in your house in a confined space. Place your generator carefully away from your home.