Chimney explosion?

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kevm14
Posts: 15201
Joined: Wed Oct 23, 2013 10:28 pm

Chimney explosion?

Post by kevm14 »

Here's how it went down.

Jamie calls me around 3:45 while she's getting Ian off the bus. She says she heard a very loud bang and the basement was smoky and the smoke alarm was going off. It seemed like there was no fire so I had her go in and shut off the water heater and furnace. The smoke had already seemed to dissipate and the smoke alarm had already shut off. I don't think either the furnace or hot water heater were running at the time she flipped them off. But it was good that she did.

Things seemed to stabilize so I went to a meeting and left work around 5pm.

When I got home I saw evidence that something had exploded, possibly in the chimney. The basement (and house) had a pretty strong diesel/oil smell. The following things had happened:
- Flue dampers on both the hot water heater and furnace pipes were blown completely off.
- Both clean out trap doors were blown open
- The big furnace flue pipe had blown apart (at a joint). See pics.

Furnace flue pipe damper. This is actually tightened down and it still blew off.
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Some of the cement had blown out from around where the pipe enters the chimney.
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This is a good one but not the worst part. Still, this joint blew apart and was hanging by one screw. The furnace would have been exhausting into the basement at this time if it was running. Good thing I had Jamie shut it off in case it tried to turn on.
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Here's some sketchiness. This is the cleanout below where the 8" furnace flue enters the chimney. This door was blown open as pictured. This looked like a normal pipe of oil soot. But inside I found a brick. I think this brick blew out of....somewhere in the chimney. Can't say I've ever opened this but I suspect it happened today.
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Blown off hot water heater flue damper.
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Blown open cleanout for the living room fireplace.
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Then I fired up the hot water heater which seemed to be working just fine and seems clean inside. I did not detect like a bunch of flue gas blowing out from that damper hole, which would indicate a chimney restriction.
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Inside the flue where the damper would normally go. I don't see anything amiss here.
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Here is a shot inside the cleanout for the living room fireplace. Extremely clean.
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More shots of the other cleanout with the brick.
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Shoveled a lot out and then vacuumed.
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Inside the flue pipe that goes into the chimney. Also seems clean in here.
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Inside the flue pipe looking back toward the furnace. Also clean though I had cleaned this not long ago.
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Then I fired up the furnace and checked for blow back and restrictions. Seemed fine, too.

Furnace has been running and other than the smell, everything seems normal.

I have no idea what happened, but both systems seem to be running clean and I think something happened in the chimney, which is kind of sketchy. But, it also currently does not seem to be restricted so maybe something built up, got hot and actually exploded and cleaned itself out?? That is messed up.

I talked to Jamie just now and here's a little more. Around 3:40 and was cleaning up some boxes. A few minutes later, she heard the "explosion" (which she described loud bang, probably also the dampers hitting the ground). She went back into the basement and it was all smoky and the smoke alarm was going off. Shortly after this she called me.

I have had my chimney inspected a while back and I already knew it was sketchy but something else happened and I'd like to know what. As of right now, things seem to be working pretty normally.

The only other thing it could have been was an ignition of raw fuel either in the hot water heater or furnace, where the burner blows a bunch of oil in, fails to shut off, and then somehow ignites it creating an explosion. This seems unlikely because it seems like it came from the chimney, rather than the hot water heater or furnace. Seems to have effected them equally.
bill25
Posts: 2583
Joined: Thu Oct 31, 2013 2:20 pm

Re: Chimney explosion?

Post by bill25 »

Um... So... now what???
kevm14
Posts: 15201
Joined: Wed Oct 23, 2013 10:28 pm

Re: Chimney explosion?

Post by kevm14 »

Everything seems pretty normal. The smell is even gone.
kevm14
Posts: 15201
Joined: Wed Oct 23, 2013 10:28 pm

Re: Chimney explosion?

Post by kevm14 »

I was up this morning around 6am or something and I could have sworn I smelled like an unburned heating oil smell. I went back to bed.

Later on, I got up and the bedroom was under 60 which isn't really normal. Jamie was downstairs and said the heat wasn't coming on, which has never happened in the 3 years we've been here. I went into the basement to investigate. Everything seemed fine except the burner shutoff was tripped, indicating it had failed to ignite and shut itself down. There is a flame sensor and if no flame is sensed, it shuts the burner down and trips that switch so it won't try again until it is manually reset.

I pressed the reset button and it lit right up.

So, with this symptom, I am inclined to agree with everyone (finally) that I did have a delayed ignition in my furnace, which is what caused that pressure event. It probably did not originate in the chimney.

Next step is basically to pull the burner, clean inside the heat exchanger, and replace the nozzle. I was hoping this can wait until the end of heating season then I can take my time as the hot water heater is a totally separate system. I just don't know which nozzle to buy and I was considering sizing it down also.

This may also be the beginning of failure for the high voltage ignitor, which is what happened to my hot water heater 2.5 years ago. I'd have to press the reset button more and more frequently until it just wouldn't light. The oil guy more or less rebuilt that burner with a new nozzle, new ignitor, and a new fuel pump. I watched him do it and there's nothing I couldn't do other than having the right parts on hand.
bill25
Posts: 2583
Joined: Thu Oct 31, 2013 2:20 pm

Re: Chimney explosion?

Post by bill25 »

I was up this morning around 6am or something and I could have sworn I smelled like an unburned heating oil smell. I went back to bed.
Good plan... LOLOLOLOLOL

Not like you had anything to worry about, like your chimney exploding. That would never happen... Twice... in a week... Um.. Yeah...

I don't think there is anything mechanically wrong that you couldn't replace, but the industry expert troubleshooting is worth something in my opinion when your house possibly blowing up is the possibility. I just spent $250 for someone to look at my kitchen stove and replace an igniter, which would have cost me somewhere between 25 to 75 dollars to do myself. I could have done it no problem, and I had already taken my stove apart to get to it just so I could see it to determine if it was the problem. At the end of the day, it lit, so I thought it was good. A professional came over and diagnosed it almost immediately. I have the peace of mind that a second opinion said it was bad because I wasn't really sure and didn't want to blow my house up. If I replaced it. I would wonder if it was really the problem, and be worried something might happen.
bill25
Posts: 2583
Joined: Thu Oct 31, 2013 2:20 pm

Re: Chimney explosion?

Post by bill25 »

I just want to say, it isn't a "you're not smart enough to do it, or figure it out". It is more an experience thing. Sometimes having someone with experience look at a situation is worth the money. Bonus points if they explain the situation so you have the opportunity to learn from an expert.
kevm14
Posts: 15201
Joined: Wed Oct 23, 2013 10:28 pm

Re: Chimney explosion?

Post by kevm14 »

The fire eye is the safety feature though it would seem the burner runs for a long time before killing the pump when no fire is seen.

Nothing blew up this time. It just didn't ignite. I bet I will need a new igniter. I don't see a nozzle causing this. I could order one. Easy to install, too. Mine is a Carlin.
kevm14
Posts: 15201
Joined: Wed Oct 23, 2013 10:28 pm

Re: Chimney explosion?

Post by kevm14 »

kevm14
Posts: 15201
Joined: Wed Oct 23, 2013 10:28 pm

Re: Chimney explosion?

Post by kevm14 »

By the way, the official name for the delayed ignition (and specially the resulting explosion) is puffback. It is a thing.
bill25
Posts: 2583
Joined: Thu Oct 31, 2013 2:20 pm

Re: Chimney explosion?

Post by bill25 »

The official name for the next stage of puffback is backdraft.
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