ᐅ Freestanding stove, room air-independent (sealed combustion system)
Created on: 2 Dec 2011 13:56
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TatzeHello stove experts and experienced users,
We are scheduled to start with the foundation slab next week.
A question has come back to our minds that we considered some time ago and now need to clarify before we begin. We want to prepare everything during construction for the later installation of a wood stove. Since we are also installing a ventilation system, the stove must be room-air independent, meaning it should draw fresh air directly from outside rather than from the indoor air.
As far as we know, there are two solutions for this. One option is to install a pipe directly within the foundation slab that connects the stove to the outside. This is the solution for which we need to decide now how to address the “fresh air” question. The second option would be to install a chimney flue with two ducts—one for exhaust air and one for fresh air.
We have already heard some negative comments about both options. For instance, the chimney sweep told us that a pipe in the foundation slab might create a cold spot. On the other hand, some people pointed out that a two-duct chimney might cause problems if, under certain weather conditions, the exhaust air is drawn back inside through the fresh air openings. My father-in-law also suggested (although he is not familiar with the system) that there could be issues with fresh air supply through the chimney itself, as it seems unclear to him why fresh air should “sink” down into the stove. He thinks that might cause difficulties when lighting the fire. Additionally, the supply and exhaust pipe connecting the chimney and stove would have a 90-degree bend sideways in our layout.
To cut a long story short... have you had experience with either system (both positive and negative)? Can you also provide some information about costs? Does the 90-degree bend cause any problems?
Thanks in advance for your responses.
Best regards,
Tatze
We are scheduled to start with the foundation slab next week.
A question has come back to our minds that we considered some time ago and now need to clarify before we begin. We want to prepare everything during construction for the later installation of a wood stove. Since we are also installing a ventilation system, the stove must be room-air independent, meaning it should draw fresh air directly from outside rather than from the indoor air.
As far as we know, there are two solutions for this. One option is to install a pipe directly within the foundation slab that connects the stove to the outside. This is the solution for which we need to decide now how to address the “fresh air” question. The second option would be to install a chimney flue with two ducts—one for exhaust air and one for fresh air.
We have already heard some negative comments about both options. For instance, the chimney sweep told us that a pipe in the foundation slab might create a cold spot. On the other hand, some people pointed out that a two-duct chimney might cause problems if, under certain weather conditions, the exhaust air is drawn back inside through the fresh air openings. My father-in-law also suggested (although he is not familiar with the system) that there could be issues with fresh air supply through the chimney itself, as it seems unclear to him why fresh air should “sink” down into the stove. He thinks that might cause difficulties when lighting the fire. Additionally, the supply and exhaust pipe connecting the chimney and stove would have a 90-degree bend sideways in our layout.
To cut a long story short... have you had experience with either system (both positive and negative)? Can you also provide some information about costs? Does the 90-degree bend cause any problems?
Thanks in advance for your responses.
Best regards,
Tatze
Hello,
I would only consider a wood stove if it is intended for occasional “fire experiences.”
If sustainable heating energy contribution is the priority, a wood stove is unsuitable due to its poor efficiency.
In that case, a masonry heater is needed. For example:
Best regards.
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Tatze schrieb:Yes, my masonry heater has an external combustion air supply. Highly recommended. The diameter depends on the respective lengths, required bends, the output of the heat generator, and the effective chimney height.
... As far as we know, there are two solutions for this. ...
I always consider a separate fresh air supply to be the better option!
Based on my calculations, the ring gap in LAS systems is usually too small, causing high pressure losses, which negatively impact the draft! This should be calculated!
[Quote="Tatze, post: 29284"]... Long story short... have you gained any experience with one system or the other (both positive and negative)?
I would only consider a wood stove if it is intended for occasional “fire experiences.”
If sustainable heating energy contribution is the priority, a wood stove is unsuitable due to its poor efficiency.
In that case, a masonry heater is needed. For example:
Best regards.
[/FONT]
Hello!
We have converted our wood stove in the new house to use an external combustion air supply. We decided against drawing air through the floor slab because we were unsure what might accumulate inside the duct over the years.
The stove does not have two separate pipes; it has a flue pipe and combustion air supplied around the outer shell of the stove. As a result:
- unfortunately, we don’t get any waste heat from the stove on the upper floor,
- the draft is rather weak (but still sufficient).
A bend in the combustion air supply should not be a problem—I have several angled sections inside the stove itself. However, a bend in the flue pipe means increased soot buildup in places that are difficult to clean.
As far as I know, our system is more expensive but doesn’t seem to be any better.
Oh, and if you are persistent, it’s possible to route the combustion air supply without visible aluminum ducting.
Best regards,
TomTom1
We have converted our wood stove in the new house to use an external combustion air supply. We decided against drawing air through the floor slab because we were unsure what might accumulate inside the duct over the years.
The stove does not have two separate pipes; it has a flue pipe and combustion air supplied around the outer shell of the stove. As a result:
- unfortunately, we don’t get any waste heat from the stove on the upper floor,
- the draft is rather weak (but still sufficient).
A bend in the combustion air supply should not be a problem—I have several angled sections inside the stove itself. However, a bend in the flue pipe means increased soot buildup in places that are difficult to clean.
As far as I know, our system is more expensive but doesn’t seem to be any better.
Oh, and if you are persistent, it’s possible to route the combustion air supply without visible aluminum ducting.
Best regards,
TomTom1
Hello,
We had the Universo chimney from Plewa installed.
It has an exhaust pipe in the center, and around the exhaust pipe, there is space within the outer shell stone for the fresh air intake.
This system works very well for us. Our stove (Nibe Contura) burns excellently. I can recommend Nibe.
The problem of exhaust air being drawn back in does not occur for us, since the exhaust air rises vertically due to the heat, and the fresh air intake area of the chimney is covered at the top with a kind of hood that only allows fresh air to be drawn in underneath it.
Now to explain how the fresh air comes in from below: Due to the heat of the exhaust air, it rises inside the chimney. This creates a slight negative pressure in the stove, which pulls in new air. The stove essentially draws this air from the fresh air intake duct. This creates a constant airflow in the stove, ensuring a clean burn.
It is also true that this means the chimney itself does not warm up, so the rooms on the upper floors are not heated.
I would definitely build this way again.
Yalta
We had the Universo chimney from Plewa installed.
It has an exhaust pipe in the center, and around the exhaust pipe, there is space within the outer shell stone for the fresh air intake.
This system works very well for us. Our stove (Nibe Contura) burns excellently. I can recommend Nibe.
The problem of exhaust air being drawn back in does not occur for us, since the exhaust air rises vertically due to the heat, and the fresh air intake area of the chimney is covered at the top with a kind of hood that only allows fresh air to be drawn in underneath it.
Now to explain how the fresh air comes in from below: Due to the heat of the exhaust air, it rises inside the chimney. This creates a slight negative pressure in the stove, which pulls in new air. The stove essentially draws this air from the fresh air intake duct. This creates a constant airflow in the stove, ensuring a clean burn.
It is also true that this means the chimney itself does not warm up, so the rooms on the upper floors are not heated.
I would definitely build this way again.
Yalta
S
Stefanlein13 Dec 2011 19:24Hello Yalta!
Basically, what you wrote is exactly right. I am also building a fireplace with an outside air supply (Schiedel Absolut).
Unfortunately, the outside air supply does not always work properly. My stove seller (very experienced) surprisingly told me that he had to disconnect the outside air supply on many stoves. They didn’t draft properly and started to smoke. Depending on the weather conditions and chimney height, such problems can sometimes occur (regardless of the stove model).
I hope for the best.
Basically, what you wrote is exactly right. I am also building a fireplace with an outside air supply (Schiedel Absolut).
Unfortunately, the outside air supply does not always work properly. My stove seller (very experienced) surprisingly told me that he had to disconnect the outside air supply on many stoves. They didn’t draft properly and started to smoke. Depending on the weather conditions and chimney height, such problems can sometimes occur (regardless of the stove model).
I hope for the best.
Hello Stefanlein,
That surprises me. It’s the first time I’ve heard of this.
However, I can only speak from my own experience, which has been very positive with this combination.
We have been heating almost daily with wood since early October and have never encountered the problem you described.
However, we need to keep in mind that when lighting the fire, the stove is not yet able to draw fresh air from the chimney. This only works once there is sufficient draft in the flue.
During the lighting phase, we have to leave the stove door ajar so it can easily draw air from the room. Only once the fire is properly burning can we close the door, and then the fire is supplied with air through the fresh air intake duct.
If you follow this process, the fire burns beautifully in the stove.
At least that’s how it works for us with our combination of fireplace and stove.
If your stove installer has had different experiences, I can’t comment on that.
Yalta
That surprises me. It’s the first time I’ve heard of this.
However, I can only speak from my own experience, which has been very positive with this combination.
We have been heating almost daily with wood since early October and have never encountered the problem you described.
However, we need to keep in mind that when lighting the fire, the stove is not yet able to draw fresh air from the chimney. This only works once there is sufficient draft in the flue.
During the lighting phase, we have to leave the stove door ajar so it can easily draw air from the room. Only once the fire is properly burning can we close the door, and then the fire is supplied with air through the fresh air intake duct.
If you follow this process, the fire burns beautifully in the stove.
At least that’s how it works for us with our combination of fireplace and stove.
If your stove installer has had different experiences, I can’t comment on that.
Yalta
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