r/Fireplaces • u/LostTwo4794 • 4d ago

Basement getting smoked out

Hello. I have a stack with 3 flues. Two fireplaces and one furnace. When I turn on the top fireplace in the first floor my basement gets smoked out. Any tips on why this is happening ( I believe theres a break in the flue) and thinking about doing a wood insert with a new vent.

We only really use the first floor fire place too so it’s constant. The smoke is worse in the beginning but I think it’s more then just a cold flue because I’ve tried to start the basement fire first to warm up the flue but it still gets smoked out

Im getting a cleaning done and want this done before winter as i use the finished basement. I attached a picture

All help/opinions are welcome. Thank you

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u/ThatllBtheDayPilgrim 4d ago

When you say turn on, I assume you mean light a wood fire. If so, I would assume it's cross over smoke at the top of the flues (not a break in the flues) since the flues are the same height. All flues are separate so one warming up verse the other shouldn't affect things. Can't tell from the picture, but I also assume they are throat dampers. Make sure basement damper is closed. Opening a window in the basement can also alleviate the problem because negative pressure is being created by using the upstairs fireplace. The basement flue will also have the weakest draft and most susceptible to reverse draft. To fix it, you need to extend the main floor flue a foot/foot and a half so smoke does not get sucked in the basement as easily when using the main floor one.

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u/LostTwo4794 4d ago

Yes I meant light a wood fire sorry. Okay thank you flues are all the same height. I’ve tried the window trick it never worked for me i actually leave my windows cracked all winter becauee of the smoke smell in basement. Im not familiar with dampers , is there an attachment or anything I can add to the tops to not allow smoke in

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u/ThatllBtheDayPilgrim 4d ago

There's either a cast iron damper right above the firebox that you need to open with a poker or turnkey (traditional) or a top sealing damper that seals the damper from the top where you pull a cord down and hook it to close the damper. I assume you have the traditional one based on what you've said. If you have throat damper and don't want a top sealing damper, they make an extender like this https://www.rockfordchimneysupply.com/products/specialty-flue-extension-with-flat-lid-base-22-in-tall

Or if you want a top sealing damper, they have these: https://www.rockfordchimneysupply.com/products/lock-top-ii-dmpr

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u/LostTwo4794 4d ago

Yes I have the traditional by the firebox. I might just get the extender it seems like the easiest way to go about it. I really appreciate you giving me this detailed info. This might be the most helpful Reddit thread lol

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u/ThatllBtheDayPilgrim 4d ago

I reread your post that you don't really use the basement fireplace. You could always stuff something up the basement flue (packed well) from the firebox. See if that works and you may not need to do anything else. Unless you do sometimes use it, then they do make flue blockers with a handle that are easy to put in and remove.