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I recently had a cap installed on my two flue chimney. The one cap covers both flues.

One flue serves a stove (Chubby) in the living room and the other is meant to serve a boiler in the basement. The basement flue is not in use at this time.

Right now I'm burning wood in the Chubby. Apparently I have a negative pressure situation which is allowing the exhaust from the Chubby to get sucked down the adjacent cold flue into the basement. I have a couple of plastic bags filled with rags plugging up the basement flue thimble and it seems to be doing the job.

I looked around online at thimble plugs and the prices are all over the place. Can anyone recommend a reasonably priced thimble plug? Thanks in advance... any other recommendations are welcome as well.

If you have a cleanout door for the flue, just keep it open till you need to use it.

Short stove pipe inserted into thimble, then a metal stove pipe cap on that.

Thanks guys. I didn't put in a cleanout for the basement boiler flue. I saw the chimney thimble cap with the crimped end online and I have a short piece of welded flue pipe that fits pretty tightly in the thimble. I might even mix up some refractory cement to fill in any voids.

When capping dual flues there should be a baffle between them.

Take a wad of fiberglass insulation and ball it up tight and stuff it in there, it'll swell up and be air tight. Cheap and easy. I did it with mine and it works great.

Okay.. I went with the pipe and cap idea. I thought it might hold up a little better. I mixed up about 2 cups of refractory cement and troweled it between the pipe and the thimble as best as I could. I had about a 1/2 " gap here and there that needed filling.

Ya got a piece of aluminum foil over the baro?

freetown fred wrote: ↑

Fri. Nov. 08, 2019 4:56 pm

Ya got a piece of aluminum foil over the baro?

No baro ... rather a 6" ID clay thimble through the basement wall to an (unused) chimney flue. This unused flue was drawing in smoke from an adjacent flue and dumping the exhaust into the basement. I capped a short piece (about 18") of 6" pipe and set that into the thimble and packed any gaps between the thimble and pipe with refractory cement.

In your other post, ya mentioned a baro in the chubby??? THE baro or A baro???

I would say what is more likely is that Your "draft" is creating a slight negative pressure and the easiest path to equalize that pressure is via that unused flue.

I would cap that unused chimney at the top.

AllanD wrote: ↑

Sat. Nov. 09, 2019 6:06 pm

I would say what is more likely is that Your "draft" is creating a slight negative pressure and the easiest path to equalize that pressure is via that unused flue.

I would cap that unused chimney at the top.

The draft in the active (adjacent) flue is creating negative pressure inside the house. Capping the basement thimble (the idle flue) isn't the best option but it seems to be working.