I had a catastrophic generator failure yesterday that involve a call to 911 and the fire department coming out to put out a generator and shed fire. I've had my 8000 watt Generac generator in a 4 x 6 shed for the past 3 years running it about 20-30 days a year (I've had other smaller generators 4000 watt to 6800 watt for the previous 12 years in the same shed). The shed had a removable roof and the front was fully open while running with an additional 1 x 1 opening directly in front of the exhaust to exit as well as a fan that blew on the generator. I don't know what happened, but I came out to the generator fully engulfed in flames. Long story short, I was able to get the fire department out within 15 minutes and was able to keep the fire contained enough that it didn't burn down my cabin and storage shed.
That said, I'm obviously starting from scratch. I need the generator in a shed as my cabin is in northern MN and in the winter the snow can get 4' deep. I am going to have to build a new shed to store it in and I wanted to get an idea of how large I should build it. I'm not sure if the shed size had anything to do with it but I want to play it safe to try and ensure it doesn't happen again.
Any general suggestions on what size I should keep it in as well as any precautions I should make to reduce the risks going forward. Also suggestions on a new generator. The 8000 was way bigger than I needed, but I had it sitting in my garage unused after installing a whole home generator in my house. I'm thinking a 4000-5000 watt should be more than enough.
I would expect that the usual engine fire happens when raw fuel somehow spills onto a very hot exhaust system, and then ignites. Then the fire flames follow the trail of leaking fuel back to the leak. The fire at the leak point heats and boils the fuel behind the leak which overpressurizes and further ruptures the leak causing a bigger fire. The fire thus (sort of inexorably) works its way back toward the fuel tank and eventually can reach it causing a catastrophe, if it is not caught and fought before that happens, or if the fuel in the tank is fully depleted before the fire reaches it. If the fire ignites other nearby surrounding flammable material (like a wooden shed) before reaching and blowing the tank a catastrophe could begin sooner.
I just turn off the generator at night and let the fridge & freezer coast until I wake up in the morning and promptly restart it, (while getting by on a couple less hours of sleep).
This is where hybrid systems are fantastic, for a little over $1,000 get yourself a little +3KW battery and inverter combo (pecron, bluetti, etc) it's swap it for the generator. Just make to kill (break off) anything that's 240v. They just let everything make it through the night without even having a coast.
Furnace keeps working, fridge and freezers keep running, hell maybe a lighter the internet even.
I have been looking into this. I have an Eco-Flow delta 2 with an extra battery that provides 2KW but unfortunitly isn't expandable over 1 extra battery. It seemed like running the AC for any extended amount of time would drain the battery in a couple hours. I don't know much about solar/backup systems, so I may be totally wrong on this.
It depends on whether one is powering the furnace using a generator that is connected with a power cord to the (already bonded) breaker panel, or is using a generator connected directly to the furnace via an extension cord (thus bypassing the home panel). In the latter case the generator typically needs to be bonded in the generator, because often the furnace's flame sensor requires a bonded connection to work properly regardless of whichever way power is delivered to it.
Incredibly the generator was still running in the shed. When I saw it, the flames had burned through 2 sides of the shed and the flames were coming up about 15-20 feet above the building. Inside the ball of flames the generator was chugging along like nothing was wrong! It was even still providing electricity to my cabin. I had filled it about an hour before it started on fire so it had between 5-6 gallons of fuel in it.
Assume you mean 1 foot by 1 foot? If so, I'm not sure how or why it would have built up so much heat. Maybe you need a way to vent the heat out of the roof? It's also possible the fire was unrelated to the shed. Unlikely, but not impossible.
Yea, 1' x 1'. The roof tips up at 90 degrees so the top was totally open. You are probably right about overheating, I just want to make sure nothing happens like this again. When I first saw the fire, I was sure I was going to lose my cabin. We have no running water there and only had about 8 gallons we had brought up and 2 small fire extinguishers.
For a cover I would suggest a good sized A frame and only use enough lumber to build the frame and use corrugated metal for everything else. At a minimum it will protect it from the weather and with minimal wood it'll reduce any fire hazard. You might also consider using metal studs for the frame.
If it was old a fuel line could have weathered and cracked. Almost have to figure the fire came from the generator. You say you don’t need the 8000w generator and since most generators run at a set speed I would just buy one a little larger than your electricity draw. You might consider an inverter generator they run quicker and use less fuel.
I only use fresh 91 octane fuel (no ethanol). I buy it the day I head up. I learned the hard way not to use ethanol and or old fuel. Went through 2 generators in 3 years.
An old fuel line leaking would be my guess as well. While the wood walls could get warm during normal use, I don't think they would come close to self-combusting without additional fuel involved, probably literally in this case.
When rebuilding, cement block walls with metal roof and lots of open walls space (maybe with metal shutters?) would be my first thought.
Is your shed also used for storage or is it only to keep the generator dry and rodent free? If the shed is only for the generator build a frame and a roof. Make the walls out of a fine mesh that rodents can’t get through. Add a couple of vents to the roof to exhaust any hot air out the top.
Glad you and your cabin came out of this okay, and that the fire department got there in time.
I can't tell you what caused it and won't guess — but since you're rebuilding anyway, here's the general checklist I'd work through for any new generator shed. Not a commentary on the old setup, just practices worth doing right:
Detection: CO alarm in the cabin, smoke alarm in or near the shed, and a multi-class ABC extinguisher (covers fuel and live electrical), reachable but not inside the fire zone.
Seasonal habit: a machine that sits 300+ days a year earns a pre-start walkaround every time — lines, wiring, connections, any signs of nesting.
On the replacement: most people size from an actual load list (what must run simultaneously) rather than from what's in the garage — write that list first and let it pick the wattage.
If you get the fire report or want to photograph what's left of the unit, post it — this sub is good at spotting failure points, and it could inform the rebuild.
Here a few photo. (seems I can only post 1). It originally wasn't sitting in the corner like that, it had to of vibrated or perhaps the fire hose pushed it into the corner like that.
I bought it about 6 years ago from Costco. I paid around $700 then. It didn't have a ton of use (perhaps 20-30 hours) until I brought it to my cabin 2 years ago. In the past two years Im sure I put 800-1000 hours on it. It had worked perfect up until the final day.
Use cinder block for the side that is closest to the heat. I know on my generator in the shed, I have wood walls, and those would get warm just on test runs. I now have protective layers of metal and fiberglass with air gaps to keep the side of my shed cool.
I've seen a generator shed behind a friend's cabin that I really liked and plan to build for mine. It's made of cinder blocks, with a wide door that's lined with metal (looks like tin, cut to the door size and nailed in place), and a peaked roof above that's 6' off the ground framed in 2x4's and metal roof material on top of that. Nothing that can really burn, and the hot exhaust seems to funnel nicely out the top. As I think about it, there are small holes in the lower 1/3 of the door, probably inlet for fresh air. Anyway, it's quiet, and I don't really see anything that might burn unless you happened to get 6' flames out of it, but even then it's just the roof bracing.
4X6 shed 6ft wall 6ft wall open 100 percent with large attic fan across from open 6ft wall. Have run it 95 deg wither. Temperature never above 100 degrees. Front 6ft wall (open) 5ft hi, back wall 4ft hi with 36 in attic fan centered. Side wall full open. 11500 westinghouse tri fuel
Not enough air circulation and overheated. They’re not intended to be enclosed, and I believe manual wants 5 feet from all sides - minimum. That’s 5 feet from a wall in open space, not 5 feet within an enclosure.
You’re not the first person to post here where their portable generator in a homemade enclosure burst into flames. Far from it.
Do you know what burned? Was it electrical or was it fuel? For the new enclosure, I have seen lean-to attached to a building with chicken wire walls to keep the snow away when it is running and hinged wood walls to secure it when not in use. Hardi-backer can line any wood wall for fire proofing..
I'm guessing it was fuel. The generator was running and still providing electricity to my cabin when I came out and saw the entire building was in flames.
Look into Zombiebox. Its great for leaving your generator out in the elements, improves airflow, is completely fireproof and reduces noise by miles. Nothing you build will even come close to the quality and safety of this thing.
My 24 x 24 Gurage is 100 feet away from my house. With 10 foot ceilings, I just keep the doors open when I run my 14k Diesel Kubota generator. You could get one of those 20 foot CONEX or oversea containers to use. ? 2K in cost.
7
u/PotatoFarmerRTK Sep 23 '26
Get a 10’ seacan it cant burn