I have a Siporex house from the 60s with an external brick chimney. The gables have a brick facade and the chimney is located in the gable exterior wall.
We have a small wood stove, and it smokes inside when we light a fire, and it's generally difficult to get the draft going without it smoking inside. I've burned a lot, so there shouldn't be a problem with my skills there.
We are planning to renovate that part soon and are considering buying a larger, more modern wood stove, but we don't want it to work poorly. We are thinking about tearing down the old chimney and installing a new one (metal pipe).
The question is, could the chimney have such poor draft just because it is in an exterior wall and gets too cold during the winter, or could it be the small wood stove we have today and the lack of its own air supply that's causing issues?
Attached is a picture of the 60s drawing showing the chimney, as well as photos from the outside and of the small wood stove we have today.
It was cleaned 2 years ago so there should not be any problems. You never know, but I believe the chimney is clean. It works, but it has kind of poor draft and I've heard that it could be because of its placement.
Could be a combination of poor intake air and difficulty getting draft in the chimney. Is there an intake air vent in the room? Open a window in the room when you light it to see if it makes a difference.
I have newly installed FTX ventilation and an air supply in that room. I open a patio door slightly when we light the fire. It gets better, but it still smokes a bit before you really get the fire going, which is uncomfortable when you're sitting on the couch. So much so that we've stopped lighting fires, you just can't handle it. Could the wood stove be of a bad type, it is very small.
I have a double-layered Isokern chimney. Made of cement and pumice stone. So, a larger inner round tube and a square outer tube.
The one you have is probably solidly built? The entire chimney takes a long time to heat up.
If my large oven has been unused for a week or more, I have to make a fire in the chimney's soot hatch first. Otherwise, smoke comes in. But after a few minutes, it draws fully.
I think the difference between my fireplace and yours is that mine generates more heat even into the smoke channel. More exhaust, so to speak. But not at a higher speed.
I see you have a relatively thick pipe, but for a small fireplace/stove. Which is likely completely cold by the next day. I have a much larger fireplace.
I load with half a newspaper, crumpled. On top, 5 - 8 split thick sticks, and as many logs. Full draft through the heavy soapstone stove.
But a cold fireplace... Then it needs to be lit a little in the chimney.
Just made a fire. Last burned a little last night. The oven was nice and warm to the touch this morning.
I have an intake air channel through the cast foundation from the outside of the stone base. Initially, we had a damper on the channel. But in my particular setup with a 90-degree bend and air in around the ash pan, the draft is perfect without a damper. We normally never adjust any draft.
Between the oven and the chimney, we have a damper, which can't be completely closed, as there's a notch in the damper plate itself. With the damper closed, no heat will escape from the oven and chimney between firings.
Your ftx is probably set for a slight negative pressure.
A burning fireplace pulls out quite a lot of air. The tightness of the house and windows affects if it can be compensated.
Most units have an overpressure mode, try if it makes a difference.
How big is the channel?
It sounds reasonable that it cools down faster and may be a little more difficult to get a draft in.
I would have run supply air to a new fireplace and if the need persists, installed a fan on top that can help with the draft.
It would be a shame for aesthetic reasons to tear down the existing one.
The chimney's height above the roof and ridge can also contribute. It's difficult to see in the picture if it reaches above the ridge. It should also be at least 1m above the roofing. It looks like there are 10 courses with stones, which, even with mortar, shouldn't be tall enough...
Your house seems to handle a really heavy fireplace...
Definitely do not switch to an open fireplace.
Or something built only in steel or sheet metal, they don't store any heat! Cold after 2 hours.
In the previous cabin, I installed a Jötul Peis 17 A...
Barely could use it. It got incredibly warm, but cold after 2 hours, once the fire had died down.
Thank you for all the answers.
We rarely use the fireplace since the main heating is geothermal. We want to be able to light a fire for coziness, but also to support heating if electricity prices remain this way.
So, we want to be able to light a fire occasionally in an unused stove and chimney without having smoke indoors.
We have a slight negative pressure set with the FTX. I would say the house is not airtight. Since it is a Siporex house, we do not have a vapor barrier inside (except towards the attic, of course).
During the renovation of that area, we considered installing an air intake from outside just for the stove. Will that make a big difference compared to an open patio door a bit away?
How much better can a modern metal chimney (pipe) that goes "inside the heat" work?
If it hasn't been swept in two years, it's definitely time to call the chimney sweep again. You'll also get an idea of the general condition of the chimney if you take the opportunity to ask. Definitely start there.
Thanks for all the responses. We rarely use the fireplace since our main heating source is geothermal heating. We want to be able to light a fire for the coziness, but also to help support the heating if the electricity prices remain this high. So, we want to be able to light an occasional fire in a rarely used stove and chimney without it smoking back.
We have a slight negative pressure set with the FTX system. I would say the house is not airtight. Since it is a Siporex house, we do not have a vapor barrier inside (except towards the attic, of course). During the renovation of that area, we planned to install an outdoor air intake specifically for the stove. Will that make a big difference compared to an open patio door a bit away? How much better could a modern metal chimney (pipe) that goes "inside the warmth" function?
Yes, but that "cozy fire" can become very expensive in the event of a fire, and if an insurance company finds out that no sweeping/control of a chimney has been done for a long time.
Your house seems capable of handling a really heavy fireplace...
Definitely don't switch to an open fireplace.
Or something built only with steel or sheet metal, they don't store any heat! Cold after 2 hours.
In the previous cabin, I installed a Jötul Peis 17 A...
Barely managed to light a fire in it. It got incredibly warm, but cold after 2 hours, once the fire flickered out.
Do you mean that the chimney seems capable of handling it, and more specifically, what is a heavy fireplace?
You mean you don't think one should have a modern wood stove?
You want to be able to light a fire in a cold stove too, it should just work. I'm going crazy with this smoke coming in.
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