Wood stove backdrafting all of a sudden

[bwells794]

I’m trying to figure out why Saturday afternoon while attempting to light a fire from cold using solely eco bricks and a half stick of fatwood in my usual “castle” formation as done in the past 2 winters, as the fatwood was burning but hadn’t yet ignited the bricks, I️ noticed a smell first and then looked over to see smoke gently rolling back into the room from the main dampers above the door (jotul f3cb). This is the first time it has ever happened and it has me worried. The chimney line hasn’t been swept yet this year, but it wasn’t really used all that heavily last year and ecobricks should be drier than splits anyway. I️ looked down the liner from the roof but could see any obstruction. The chimney cap has a grill that would prevent pretty much anything but bugs and pine needles from getting into it. Then I️ though maybe it only being 51degrees out might have something to do with it, but I tried it again this morning at 31 degrees with the same result. I️ have a sweep kit and can try brushing it out really good but I️ don’t think creosote is the culprit.

TLDR; 3rd winter of burning, never backdrafted until this weekend, wood is dry, backdrafts before I️ can even get full ignition of the wood. It’s like there’s no draft at all and instead cold air is just like piledriving down the chimney and won’t let smoke up. Any ideas what might be going on? Thanks!

 

[EJL923]

whenever i read a post like this, i look at the member location. possibly warmer area, less draft. Also if it was raining with heavy air around. Usually once a year, in the shoulder seasons this will happen. Once that masonry gets warm, never an issue. When it does happen, keep the door cracked for a second. Make sure you stick around.

 

[2fireplacesinSC]

Not 100% sure what all you mean. Is it actually reversed draft and putting cold air in the house?

From what you've said, I would do a quick sweep and double check the chimney cap. Then, to light the next fire, consider using a blow torch (not onto metal, pointed up chimney) to preheat the chimney for a minute or 5. Sounds like could be a shoulder season issue though related to masonry temperature, house temperature, outdoor temperature causing air movement reversal.

 

[bwells794]

Not 100% sure what all you mean. Is it actually reversed draft and putting cold air in the house?

From what you've said, I would do a quick sweep and double check the chimney cap. Then, to light the next fire, consider using a blow torch (not onto metal, pointed up chimney) to preheat the chimney for a minute or 5. Sounds like could be a shoulder season issue though related to masonry temperature, house temperature, outdoor temperature causing air movement reversal.

Yes, it almost seems like reverse draft, but it’s gentle. I️ don’t think it would blow a match out but it was certainly “directing” the smoke from a small lit piece of fatwood out into the room when holding it in my hand inside the firebox. That being said, the central air wasn’t on, no kitchen or bathroom fans were on and the dryer wasn’t running. I️ will try to sweep it this evening and see what happens. I’m not exactly excited at the prospect of having to preheat my chimney with a blow torch every time I️ want to light a fire and shouldn’t have to as I️ mentioned I️ have burned 2 seasons before this and even several loads THIS season already. It’s not particularly windy (if at all) and nothing has changed as far as trees or chimney height since I️ got the stove. We shall see what happens.

 

[jatoxico]

Just for clarity, the cap is clean? They are often the culprit especially the "screen" types.

 

[bwells794]

Just for clarity, the cap is clean? They are often the culprit especially the "screen" types.

Yes, cap is clear. It’s not a very dense screen, just enough to keep a bird or the like out. And has a rain shield. I️ went up there on Saturday just to make sure there wasn’t some super obvious thing wrong or impeding the flow of air.

 

[jatoxico]

Check that the baffles/insulation blankets etc are in place and not obstructing.

 

[blades]

you would not have to use a blow torch a hair dry works, even in the output from shop vac is enough to get things going in the right direction after checking the internals of the stove are proper located as mentioned.

 

[begreen]

Could be multiple things. Barring an obstruction in the flue system (bees nest, etc.) take a look at the house. Is there an upper story window or attic vent open? Was there a large or multiple exhaust fans running (including dryer)?

 

[bwells794]

Could be multiple things. Barring an obstruction in the flue system (bees nest, etc.) take a look at the house. Is there an upper story window or attic vent open? Was there a large or multiple exhaust fans running (including dryer)?

Single story home. No fans, exhaust or dryers running. Little cold for bees to have constructed a nest large enough to block the chimney within the last 7-10 days.

 

[begreen]

Stuff happens, sometimes it can be at odd times or locations. I'm not saying this is the issue. It's just one of the things to inspect and cross off the list in problem solving. Similarly an open attic vent can cause negative pressure in the house. We can't see what you see and know, so it takes a lot of questions to catch up. Pictures can help here too.

Can you describe the flue system from stove to chimney cap? How is the F3CB connecting to the chimney? How tall is the flue system?

 

[bwells794]

The stove is sitting on the hearth which sits maybe 6 inches off the floor, rear exhausted with 6” SS liner kit, T connector with cleanout cap, liner was ovalized at the bottom to get through the chimney damper then circalized (if that’s a word) again to be able to mate with the T. Before it is said, I’m aware this is not the most ideal setup but it is the way a professional installer said they would have done it and as mentioned earlier, it has worked supherbly for 2 winters thus far. Liner is not insulated but the same dealer said that it was not needed in my case. It was a 25’ liner kit and I️ still have about 6-8’ of it in the garage so that should give you an estimate to stack height. Cap came with the kit, screened to prevent animals from getting in and has a rain shield.

 

[bwells794]

Update: no luck. There nothing in the liner but I️ swept it anyway. Zero draft. I’ll probably just wait until the summer and have someone come look at it.

 

[begreen]

This can sometimes be chimney location and even geography. An uninsulated liner is not helping if draft is weak. As a test you could remove the cap, then take a 4' length of cheap 6" round stove or duct pipe and insert it crimp down into the existing chimney, then see if draft is notably improved.

 

[bwells794]

I️ just can’t help but think this is something beyond how I️ have it setup. If I️ had just bought the thing and couldn’t seem to get it to pull, then I️ would doubt the configuration. But as I️ said before, this thing has pulled like a champ for two years and now it just doesn’t. I’m over here scratching my head.

 

[Squisher]

Check that the baffles/insulation blankets etc are in place and not obstructing.

Double check this.

Then if it's all good try lighting it with a nearby window cracked.

 

[Supersurvey]

Try using one of the sterno's (the kind you use to heat food trays) to warm the chimney for a few minutes.

 

[moresnow]

Any chance your primary air control is not opened up? Guessing it is but ya never know!

 

[begreen]

Very strange. The F3CB top is removable. There is an allen screw on each side of the top that can be removed to release the top. That would allow you to inspect the top of the baffle. Or the tee could be disconnected from the flue collar for inspection in both directions. If that is done you could also take a punk or cigarette and see if there is any draft pulling in the smoke. If the test shows that draft is weak, repeat the test after a nearby window opened slightly and see if there is a change.

Also, make sure the tee cap is on snugly and not leaking.

 

[nola mike]

How cold was your house? I'll sometimes get a reversal if I'm out of town for a few days and the house is cold, and/or I haven't been burning for a while. As others have mentioned, heat the exhaust with a blowtorch/hair dryer for a few minutes. I'll then light a piece of newspaper to make sure it's drafting in the right direction. If so, I'll make a small newspaper fire, then start a fire as normal.

 

[woodsplitter82]

A downdraft can be a pain ! I usually use some newspaper and a little charcoal lighter, not much lighter, though, or may cause a unpleasant smell. I finally got online and purchased a inline 6" draft blower, that installs directly into your chimney. Just turn it on and the draft immediately charges up the chimney. You can even run it on low to start a fire. Also these draft blowers come in different sizes to fit your chimney. It was a life saver for me !!

 

[spolleypt]

I know this is old, but I had a similar issue this year. After trying to light a fire and having it barely burn for about 15 minutes, I looked over and saw the cleanout door was wide open. Explained the smell I couldn't figure out either. Not sure what caused the door to open but alas it has happened again this morning. I think it has to do with not letting my fire and chimney get hot enough before closing it down for the night.

 

[begreen]

Run a thick bead of silicone around the sealing edge of the door, then close it. That should form a decent gasket that will also hold the door closed.

 

[spolleypt]

Run a thick bead of silicone around the sealing edge of the door, then close it. That should form a decent gasket that will also hold the door closed.

Thanks! If there is a backdraft and the clean out is sealed would it create an issue somewhere else? I’m assuming at the stove would be only other area for pressure to equalize??


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[begreen]

Is the cleanout much lower than the stove, like in the basement? If so, it might not affect the stove, particularly if the cleanout is in a negative pressure zone and the stove is in a neutral zone. Eliminating upstairs air leaks will also help. This could be sealing up an attic door, leaky windows, etc..

Draft improving measures may also help. Is the chimney liner insulated? Does the stove pipe come up to a 90º elbow or has it been softened with a pair of 45s and an offset?