Down draft problem With fireplace, behind insert

[Jake]

Hi guys, I haven't been here in a long while...

We also haven't burned much in the past few years

The last couple of summers, my wife has commented that when the AC is on, there's a musty/organic smell in the room with the insert.

This happens to also be the closest room to the furnace so we just chalked it up to our a/c blower unit needing a good cleaning and never did much about it.

This summer, my wife spends all day in the room with a new born and the smell is driving her crazy.

She has determined that the smell is coming from the fireplace itself and not the insert. Ive confirmed this too, there's almost no smell in the insert w the door open, but its very pungent at the top of where the surround meets the brick.

How do I fix this??

Other info that may or may not be useful
I have a full liner.
We bought the house in 2005, and called a chimney sweep. The sweep commented that he would guarantee our house would burn down if we used the fireplace. do to the condition of it. He gave us a 15k estimate to fix it.

A few years later we got an insert and haven't had a problem.

 

[BrotherBart]

Just shooting in the dark without being able to see the setup and chimney but willing to bet that if the chimney is in that bad of a shape that water is leaking down from the crown into the firebox and mixing with old deposits and causing the smell.

Pull the surround and see what is going on back there. I am willing to bet you will see evidence of water having been on top of the insert if it is a crown leak.

 

[webby3650]

What condition is the chimney crown in? A cracked crown is a very common place for water to infiltrate. How is the mortar?
I was having some water making it's way in, I tuck-pointed the areas that needed it, cast a new concrete crown, and then water proofed the entire thing. I have had no more issues.

If the crown is in decent shape, you might get away with a crown coat and a good waterproofing.

 

[webby3650]

Here is what the new crown looks like. The old one was mortar and had no overhang. I also added new counter flashing. The overhang and waterproofing is really the thing that makes the biggest difference.

 

[Hogwildz]

Could be condensation if your running AC. Also, do you have a block off plate closing off the damper area?
Yet another good reason for a block off plate.

 

[Jake]

No plate, I'll post some pics in the am

 

[Hogwildz]

No plate, I'll post some pics in the am

That may be your problem, or a big part of the problem.
No block off is letting the conditioned air up and cool inside Vs. hot outside is going to cause condensation.
Does the wife notice it more on humid days?

 

[J.Stempel]

Not sure if this helps but I'll take a shot...

Before we put in our insert, any change in pressure in the house or any time we sat in a room adjacent to the fireplace, we were constantly assaulted with the odor of something I assumed was creosote and old fireplace residue, always worse before emptying ashes but even after was pretty strong. The house was built in 2000 and we burned oak and fir mostly through the winter. In summer the odor was so bad I finally had to tape the entire opening closed with 3 mil plastic and duct tape, and after about an hour the smell was gone. After a few days you couldn't detect it in the sofa, etc. So we had plenty of time to ascertain that this particular god-awful smell was from the firebox itself and had nothing to do with the chimney.

After installing our Jotul 550, I noticed a couple of times we would get a bit of that odor when we would kick on the fan during a fire. However, we only used it a short while since this May when it was installed. About a month ago, when we first ran the AC, within 15 minutes the smell was back as bad as ever. I was hugely disappointed since part of my rationale for shelling out the money for the unit was to finally be rid of the odor, presumably by blocking the opening. First thing I did was block the air slot on top where the hot air is blown out because I could smell it coming from there, and that eliminated some of the issue. About a day later my wife and I could smell it pretty badly still. It was clear that the thin sheet metal surround that overlapped the brick face was doing almost nothing to really block airflow from the firebox into the house - you could pull the metal surround back an inch or so and get a strong whiff. To test my theory I sealed all three sides off with painter's tape and the smell disappeared for good regardless of whether we had our kitchen exhaust fan on, A/C, etc...

So - two weeks ago I bit the bullet and tried running a heavy bead of heat-rated caulk between the brick and metal. I put painters tape on the brick and also on the metal surround to catch any stray caulk. I rigged up a system to use a piece of 2x4 to lay against the 3 sides (I just did one side at a time, leaving the brace n place for a few hours) to ensure the metal and brick were sealed tight. Took about an hour.

Since doing that there isn't a shred of odor.

I figure in the winter when I pull the dishtowel out of the air-blower slot I can deal with the smell or rig up a metal plug to fit the opening.

So my guess is you have creosote odor seeping in around the sheet metal. You could use the painter's tape method as a trial if you like. Let me know if you want to know what type of sealer I used.

Good luck.

 

[Jake]

Here's some pics,

 

[begreen]

I would try adding 12" height to the wood stove vent.

 

[TradEddie]

I had the same problem, although probably not as bad as yours sounds. A blockoff plate may help, but even with a perfect seal at the blockoff plate, air is still free to come down the liner through the stove and out into the room. It is a requirement of EPA stoves that even with the damper fully closed, the stove must still have some air path. I modified my damper to override this, I can now totally seal the insert when not in use and have not had a single whiff of smoke this summer. I installed a blockoff plate about the same time, so i can't say for sure which fixed the issue.

I posted pics of my air mods if you take the time to search.

TE

 

[granpajohn]

What condition is the chimney crown in? A cracked crown is a very common place for water to infiltrate. How is the mortar?
I was having some water making it's way in, I tuck-pointed the areas that needed it, cast a new concrete crown, and then water proofed the entire thing. I have had no more issues.

If the crown is in decent shape, you might get away with a crown coat and a good waterproofing.

Similar story here.
We didn't get odor, but I found moisture in my insulation, and a little surface rust.

 

[webby3650]

Is there a crack between the clay flue and the crown? Might put some concrete crack filler around it. In pic #3 the stone has some blackness, which is caused from water running down the stone, water might be able to run under that overhang on the crown if there is no cut or recess cast into it. The cut on the underside of the lip allows water to drip off when it hits it, otherwise it can return all the way back to the stone and make it's way in through any of those hairline cracks in the the mortar.

 

[webby3650]

Similar story here.
We didn't get odor, but I found moisture in my insulation, and a little surface rust.

I didn't have an odor either. I sold my insert, when I pulled the panels off I was shocked to see rust on top of it! A few days after I cleaned everything up it rained for a few days. On day two of a soaking rain, I heard a slight drip, I never saw the water, but it was seeping in and dripping on the front side of the damper frame. I haven't had a drip since I completed the new crown and waterproofing!

 

[BrotherBart]

Yeah but that smell being around the surround spells moisture in the chimney. Not downdraft in the liner.

BTW: I would not kill but would significantly maim to have a nice chimney crown like that.

 

[begreen]

I thought I saw a little smoke coming from the adjacent low flue in the last picture. Is that true or just lens flare?

 

[BrotherBart]

I don't think a leak from it could get into the fireplace but the base of that chimney is in serious need of a good flashing job.

 

[Don2222]

Here is what the new crown looks like. The old one was mortar and had no overhang. I also added new counter flashing. The overhang and waterproofing is really the thing that makes the biggest difference.

Excellent pic. Great Job. Did you cut and bend that sheet yourself?

 

[TradEddie]

Oh yeah, I replaced my crown too, so it could have been any one of the three that fixed my smell. I wouldn't dare to show pics of my crown repair compared to those pics above.

TE

 

[Hogwildz]

In the summer, I find it hard for hot air to draft down a chimney into a cooler piping, stove and room.
The base flashing around at the roof line looks like it has a lot of caulk on it. Technically, it should be set into a reglet that is cut into the masonry. But if good caulk is used and it is a tight seal, may not be an issue.
The top plate should have been bent down on all four sides so that it dropped over the edges of the old clay tile op. The have it flush on top with caulk around it. I would inspect that real good and look for any gaps, fish mouths etc that may let water run in.
I still say if you don't have a lower block off plate in the damper area, sealed well, you may be getting condensation inside the old flue.

 

[J.Stempel]

My 2 cents about the issue of moisture: I heard this numerous times from other sources as well when it came to our odor issue. That said, it was just as bad if not worse in summer here in Oregon, after 50 days of 80-90 degree weather and zero precipitation. Seems like you either determine the odor is a product of airflow from within the circulation of your insert/liner apparatus or else it's residue from the original fireplace. Doesn't seem like it needs to be so complicated.

 

[jdp1152]

we had downdraft issues when it was an open fireplace and when it was insert converted. Supposedly a sealed block off plate was installed at the time....well, it wasn't sealed. Some furnace cement helped tremendously, but there were still days I could get that fireplace smell. You have to address pressure issues in your home in addition to the insert. A temp fix is to light a candle in your insert to get the air flowing up the flu, but overall, you have to address air leakage in the home. We were battling smoke spillage on every reload. After converting from baseboard heat to forced air, it was very very very apparent where we were losing heat/accepting heat over the year. Behind the metal baseboards...sometimes an inch of space from dry wall to floor. In the main living room, there was even a hole drilled to the outside where some kinda speaker wire was run. Baseboards removed, sealing performed, house wrapped with Tyvek before replacing siding and we haven't experienced that odor this summer. When air is leaving your home from other points faster than it does your chimney, it pulls the replacing air from where ever there is a crack in the envelope. The flue is an easy point. Start at the top of your home and start sealing. It's much more valuable than insulation. Energystar has a nice air sealing guide on where to look and focus your efforts. I emphasize starting from top down to lower than negative pressure plane. It needn't be perfect, but you have to reduce air leakage.

I can't pinpoint exactly what I did to solve the issue because we did many things. Attics spray foamed, sealed the basement rim joist and replaced/sealed all doors there, air sealed attics even though we had the foam, pulled off all baseboards and window trim and sealed and replaced...we haven't had those issues since that happened. If it's not new construction, you're not going to remove the pressure issues, but you can lower them to below the fireplace plane and that should be your goal.

( google stack effect, chimney odor, negative pressure) and you'll find advice more detailed than mine. Bottom line...air sealing your home is the best thing you can do in an older home. You'll still be able to burn without issues because the air changes per hour in a older home will still be 1.5 or better with just home remedies and not a complete deep energy overhaul.

 

[J.Stempel]

Excellent points about air leaks. In our case that's a feature, not a bug. Between a radon mitigation system and a 140 pound Mastiff that necessitates a 24/7 fan in the mud room negative pressure is a given.

 

[Jake]

Tonight we took plastic and masking tape and taped off the whole insert, Smell is gone. Obv I can't leve it like that, I'll strt looking for water leaks

 

[webby3650]

Excellent pic. Great Job. Did you cut and bend that sheet yourself?

Yes. I wish I had a before picture, I always for get that part.