ᐅ Freestanding stove, room air-independent (sealed combustion system)
Created on: 2 Dec 2011 13:56
T
Tatze
Hello 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
Yalta schrieb:
....However, we need to keep in mind that when lighting the stove, it is not yet able to draw the supply air from the chimney. This only works once there is sufficient draft in the exhaust duct. During the ignition phase, the stove door must therefore be left slightly open so it can easily draw fresh air from the room. Only when the fire is burning well can we close the door, and then the fire will be supplied through the air intake duct. This means it is not airtight to room air. Also, a preheating flap seems to be an unfamiliar term here.Best regards.
Hello €uro,
you are making it too easy for yourself.
The stove was sold to me as room air-independent according to the DIN standard, and the chimney sweep also approved it as such.
So the question is, how the term "room air-independent" is defined. Our ignition phase lasts a maximum of 2 minutes; then we close the door, and the chimney draft starts. From that point on, the stove is supplied exclusively by the external air intake.
For another, more expensive stove from the same manufacturer, the stove fitter even advised us against it because it can only be supplied by external air intake but does not meet the stricter requirements of room air-independence.
Who is right here (you, or our stove fitter and chimney sweep), I do not know. The important thing is that the stove works very well with this chimney, and it does.
I researched the ignition flap and found the following:
Quote:
"The ignition flap is a so-called short-circuit flap for the flue gases.
In unfavorable weather conditions and/or during ignition, the chimney draft is often not strong enough to draw the flue gases out of the combustion chamber – the stove smokes. With the ignition flap, the flue gas path is 'shortened.' This can be controlled either manually or automatically. Once the chimney draft is established again, the flap closes and the flue gases can take the longer path through the stove without problems."
Such a flap only makes sense if the flue gases have to travel a long way through the stove before reaching the chimney. This path can be shortened by the flue gas flap to improve the ignition phase.
1. This is initially independent of whether an external air supply is installed or not. That means external air supply is not a mandatory prerequisite for an ignition flap.
2. Only the design of the stove determines the usefulness of an ignition flap. If the flue gas path cannot be shortened because the shortest possible path is already defined, then such a flap brings no benefit. This is the case, for example, with our Swedish stove.
Ultimately, it is as follows:
The chimney itself works as the driving force for the air draft through the stove. Only when the chimney is sufficiently filled with warm air is the rising air strong enough to pull the exhaust gases out of the stove and bring in fresh air.
In modern low-energy houses, very low output stoves are often used because otherwise, it simply gets too warm. We have only a 4 kW (13,600 BTU/hr) stove, which is completely sufficient to comfortably heat our living area.
How a stove with such low heating power could manage to start the chimney draft without help... I think this is exactly the problem for the people mentioned by Stefanlein, who have their external air supply removed again.
Yalta
you are making it too easy for yourself.
The stove was sold to me as room air-independent according to the DIN standard, and the chimney sweep also approved it as such.
So the question is, how the term "room air-independent" is defined. Our ignition phase lasts a maximum of 2 minutes; then we close the door, and the chimney draft starts. From that point on, the stove is supplied exclusively by the external air intake.
For another, more expensive stove from the same manufacturer, the stove fitter even advised us against it because it can only be supplied by external air intake but does not meet the stricter requirements of room air-independence.
Who is right here (you, or our stove fitter and chimney sweep), I do not know. The important thing is that the stove works very well with this chimney, and it does.
I researched the ignition flap and found the following:
Quote:
"The ignition flap is a so-called short-circuit flap for the flue gases.
In unfavorable weather conditions and/or during ignition, the chimney draft is often not strong enough to draw the flue gases out of the combustion chamber – the stove smokes. With the ignition flap, the flue gas path is 'shortened.' This can be controlled either manually or automatically. Once the chimney draft is established again, the flap closes and the flue gases can take the longer path through the stove without problems."
Such a flap only makes sense if the flue gases have to travel a long way through the stove before reaching the chimney. This path can be shortened by the flue gas flap to improve the ignition phase.
1. This is initially independent of whether an external air supply is installed or not. That means external air supply is not a mandatory prerequisite for an ignition flap.
2. Only the design of the stove determines the usefulness of an ignition flap. If the flue gas path cannot be shortened because the shortest possible path is already defined, then such a flap brings no benefit. This is the case, for example, with our Swedish stove.
Ultimately, it is as follows:
The chimney itself works as the driving force for the air draft through the stove. Only when the chimney is sufficiently filled with warm air is the rising air strong enough to pull the exhaust gases out of the stove and bring in fresh air.
In modern low-energy houses, very low output stoves are often used because otherwise, it simply gets too warm. We have only a 4 kW (13,600 BTU/hr) stove, which is completely sufficient to comfortably heat our living area.
How a stove with such low heating power could manage to start the chimney draft without help... I think this is exactly the problem for the people mentioned by Stefanlein, who have their external air supply removed again.
Yalta
Yalta schrieb:
...you are making it too simple for yourself. The stove was sold to me as room-air independent according to DIN standard, and the chimney sweep approved it as such. That doesn’t necessarily mean that it actually is. Check the DIBT approval number (certificate)! Yalta schrieb:
...Regarding the firing flap, I researched and found the following:
Such a flap only makes sense if the flue gases have to travel a long way through the stove before reaching the chimney. This path can be shortened by the flue gas flap to improve the lighting phase. Absolutely correct, because longer paths guarantee maximum energy efficiency! Yalta schrieb:
...In the end, it is like this:
The chimney itself acts as a driving force for the draft through the stove. Only when the chimney is sufficiently filled with warm air is the rising air strong enough to pull the exhaust gases out of the stove and draw in fresh air. Wrong, sufficient draft must be present even with cold air, possibly supported by the effect of a firing flap. That is precisely what it is intended for! Best regards
Hello,
I'm bringing this topic back up.
We are planning a mechanical ventilation system with heat recovery and also want to install a fireplace. We understand that we will inevitably need a pressure switch, but that’s not our main concern.
Until now, we assumed that a chimney with dedicated fresh air supply would be sufficient. We recently consulted a fireplace specialist who recommended supplying fresh air through a drainage pipe installed beneath the foundation slab. In principle, this sounds interesting and quite reasonable.
After this long introduction... Our main concern is that this solution might introduce a cold air source into the well-insulated house. What are your thoughts on this? How do you see it?
Thanks...
I'm bringing this topic back up.
We are planning a mechanical ventilation system with heat recovery and also want to install a fireplace. We understand that we will inevitably need a pressure switch, but that’s not our main concern.
Until now, we assumed that a chimney with dedicated fresh air supply would be sufficient. We recently consulted a fireplace specialist who recommended supplying fresh air through a drainage pipe installed beneath the foundation slab. In principle, this sounds interesting and quite reasonable.
After this long introduction... Our main concern is that this solution might introduce a cold air source into the well-insulated house. What are your thoughts on this? How do you see it?
Thanks...
Yalta schrieb:
the rooms on the upper floors are not heated.which by the way is an ADVANTAGE, not a disadvantage. We use the exact same approach, and if it got warm upstairs, our bedroom would be like a sauna. When we want to heat the whole house, we open the living room door and let the heat rise into the hallway above.
The less heat is wasted anywhere in the house, the better the chimney is insulated, the more efficiently the stove burns, and the less heat loss there is (warmth in the room where you are heating).
Payday schrieb:
which, by the way, is an ADVANTAGE, not a disadvantage. We use exactly the same system, and if it gets warm upstairs, our bedroom becomes like a sauna. When we want to heat the entire house, we open the living room door and let the heat rise into the hallway.
The less heat is wasted anywhere in the house, and the better insulated the chimney is, the faster the stove burns cleanly and the less heat loss there is (heat stays in the room where you are heating)Hello Payday,
Replying to a three-and-a-half-year-old post... But thanks anyway!
However, coming up with an idea or an answer to my question doesn’t seem that easy... Maybe someone else can add something. Thanks.
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