Basement getting smoked out

[u/LostTwo4794]

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

[u/ThatllBtheDayPilgrim]

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.

[u/LostTwo4794 → u/ThatllBtheDayPilgrim]

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

[u/ThatllBtheDayPilgrim → u/LostTwo4794]

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

[u/LostTwo4794 → u/ThatllBtheDayPilgrim]

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

[u/ThatllBtheDayPilgrim → u/LostTwo4794]

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.

[u/mrseantron]

Your picture is tricky due to perspective, but it looks like all your flues are at roughly the same height, which is a recipe for downdraft problems. I'd look at raising your top floor flue by at least 12". But if there's a break in the flue, don't use it at all, because it's not safe.

[u/LostTwo4794 → u/mrseantron]

Yes they are all the same height, thank you for your input I will have to raise the one we use

[u/Lots_of_bricks]

Likely stack effect more often than cracks in the flues allowing smoke to traverse between them. Stack effect is the homes pressure differential and the outside conditions. Installing a top mounted damper system on the basement fireplace usually stops this issue. But if u do not intend to use it then save money and seal the top of the basement flue with some metal and silicone.

A wood burning insert and liner will be a great addition to the upstairs fireplace but it can potentially still have the same issue with smoke falling down the basement flue if u don’t seal it.

[u/LostTwo4794 → u/Lots_of_bricks]

Thanks for the reply. I hope Thats it. I might get the extender for the upstairs first and hopefully that gives it enough clearance. We go through a lot of wood upstairs so I think the stove will be more efficient anyways

[u/Lots_of_bricks → u/LostTwo4794]

Try just sealing the top of the basement flue 1st. Extenders dont always work, won’t work with the insert/liner system and can be expensive. An seal the top of that flue for less than 20$ and can easily remove if necessary

[u/ThatllBtheDayPilgrim → u/Lots_of_bricks]

I reread that he doesn't really use the basement, he could stuff something up the basement flue from the fireplace (free) and see if that works for now.

[u/Lots_of_bricks → u/ThatllBtheDayPilgrim]

Be better to seal at the top tho. Would ensure the smoke was actually from the top and not traversing a gap in the tile liners.

[u/LostTwo4794]