UPDATE 6/2017: Having re-tested this design with generator under moderate -> heavy load, not in econo mode, for a sustained period I felt exhaust side temps were too high. Small sections of plastic bread keeper on exhaust side got > 90c. Ordered 240CFM replacement fans & will be using a $18 steel mailbox on exhaust side, with larger/taller outlet side hole, to see how that works/helps. My prior tests were shorter / lighter load / econo mode ones.
Noise bothers me more than most. Though the Yamaha EF2000is and Honda EU2000i are among the quietest and most reliable generators they still make noise. This project was inspired by boondock camping and having to charge camper batteries every couple/few days. For example if you find yourself in a campground or park that allows generators during certain hours but has mostly tent campers OR limits generators to onboard ones (using an enclosure should get you by). Also useful for emergency use in subdivisions with smaller lots.
(UPDATE: Of course there's been other somewhat similar efforts but hadn't found one at this particular size/cost/weight/effort/efficacy point)
Very happy with performance so far (see UPDATE 6/2017) and box is easily portable and makes a great storage/travel box for generator. BUT you've got to REALLY want this thing to go through the trouble & expense (<= $150?) of building it:)
Standard disclaimers apply, you build this project at your own risk and take full responsibility for any consequences. This project directly violates product warnings and warranties and introduces possibly flammable materials in close proximity to the generator.
I built this enclosure in the Fall of 2015 and have used it a few times for several hours each since then, so not extensive use. Measured generator case temperatures and they did not differ much from generator outside of box (see UPDATE 6/2017). Box has dual fans, intake and exhaust, so should survive one of them failing. Think key risk is the adhesive properties of sound deadening materials, do not economize there. As always generators are not to be run unattended.
Step 1: How Much Quieter With Box
Here's results from a sound test I performed on my driveway. Sound levels are noticeably lower on gravel or dirt vs pavement which conducts/reflects sound. Pretty satisfied with the sound reduction, especially in upper frequencies that are most annoying.
Step 2: Materials
Will probably forget some things as built this 18 months ago. Here's what I remember using:
* Blue Hawk 27-Gallon Plastic tote with lid (131957) available through Home Depot, Lowes, etc.
* 2 "120mm 25mm Case Fan 12V DC 124 CFM" via eBay. Fan physical size is critical, CFM should be higher e.g. 240 - 252 CFM(?), see UPDATE 6/2017.
* 12V supply line/plug for your generator, billed as a battery charge line.
* 2 "Rubbermaid Specialty Food Storage Containers, Bread Keeper, Red (1832489)" via Amazon. UPDATE 6/2017: inlet side this is fine, outlet side may be too hot - trying metal mailbox next.
* "[4 Pack] Mybecca 2-inch Acoustic WEDGE Premium Studio Soundproofing Foam Wall Tiles 12 x 12 x 2 Inches" via Amazon
* "Fantasycart Automotive Sound and Heat Deadening Insulation Mat 88"x39"", adhesive backed, via Amazon. There are thicker, more effective & pricy engine noise barriers options.
* 3M Hi-Strength Spray Adhesive via Home Depot for wedge foam tiles pieces
* Screen to cut for intake sides of fans, box top grab handles, clear plastic/handle/hinge (mine was a kitchen cabinet spring open one) for door, ZIP ties, 2-conductor cord, small L-brackets, nuts & bolts, sheet of something to sit under generator during storage.
Step 3: Construction
Hopefully evident from the photos:) Key bits for my Yamaha EF2000is build:
* Placement & holes in Bread Keepers - Keepers should be about 3.5" up from box opening/ground for air/handle clearance. Holes should be large and roughly aligned with intake & exhaust, especially exhaust so that it exits directly though hole into bread keeper. Holes should extend from above fan locations to below top allowing clearance for mounting bolts, fan L-brackets. UPDATE 6/2017: Trying steel mailbox on exhaust side + larger hole.
* Fans are wired in parallel, mounted about 2" up into bread keepers & held only on box side by 2 small L-brackets and, after rounding fan outers slightly, they'll wedge fit into keepers. Screens are ZIP tied to intake sides of fans (w/short spacers) to keep any debris from fouling fan. Fans blow toward their label sides, generator intake side (right) blows in/up, exhaust side (left) blows out/down. Fans connect in parallel to generator's 12V charge line/wire/plug, solder & use heat-shrink tubing over connections.
* I washed/cleaned plastic box & bread keeper interiors well prior to applying materials, using 90%+ alcohol as a final wipe. The automotive hood deadening insulation is pesky stuff to measure, cut & fit - wants to stick before in place. The acoustic wedge placements are particular to EF2000is and serve to cut noise & also help center/properly position lid when lowering onto generator. Use sparingly & pay attention to acoustic wedge direction, you want right-to-left (intake -> exhaust) air flow through box. Use plenty of 3M Spray Adhesive on both side for acoustic wedges during fitment.
* Box makes great storage/travel container for generator. Don't lift box with generator in it, place box with sheet of something like plastic in its bottom for support then fit generator when storing.
Step 4: Testing
Be sure to fully test generator with cover prior to actual use. I used my house refrigerator as heavy load test, using heavy extensions (12/14 AWG?) for a few hours with generator/box in sun for my initial test. Compared temp measurement by hand & infrared thermometer on generator in & out of box and found them to be fine.
UPDATE 6/2017: Design needs changes for sustained moderate -> heavy load use.
Since the test I've used this combo on a couple camping trips and its worked well, of course YMMV.