Fireplace stove, independent of room air

Hello fireplace experts and experienced users of such,

we are supposed to start with the base slab next week.
Now a question has come back to our minds that we had already thought about some time ago and that we now need to clarify before we start. Specifically, we want to make all preparations during construction for a later installation of a fireplace stove. Since we are also installing a ventilation system, the fireplace stove must be room-air-independent, meaning it should not draw its fresh air from the room air but directly from outside. As far as we know, there are two solutions for this. One could have a pipe built directly into the base slab that connects the fireplace stove and the outdoor area. This is also the solution for which we now need to decide how to settle the "fresh air question." The second option would be to install a chimney in which two pipes run, one for the exhaust air and one for the fresh air. Now we have already heard negative things about both variants. On the one hand, the chimney sweep told us that the pipe in the base slab would represent a cold source. On the other hand, people warned us that with the two-flue chimney there could be problems with the exhaust air possibly being sucked back in through the fresh air openings (depending on the weather). My father-in-law also said (although without knowing the system) that there could be problems with the fresh air through the chimney itself, because it seems incomprehensible to him why the fresh air should "sink" downward into the fireplace. In his opinion, this could cause problems when igniting. In addition, the exhaust or fresh air pipe connecting the chimney and fireplace would have a 90-degree bend to the side in our case.

Long story short... have you already had experience with one system or the other (both positive and negative)?
Can you also say something about the costs?
Does the 90-degree angle pose a problem?

Many thanks in advance for your answers.

Regards
Tatze

Hello,

... As far as we know, there are two solutions for that. ...
I always consider a separate fresh air supply to be the better option!
The annular gap in the LAS systems is, according to my calculations, usually too small, causing high pressure losses, which accordingly affects the draft! That should be calculated!
[Quote="Tatze, post: 29284"]... long story short... have you already gained experience with one system or the other (both positive and negative)?

Yes, for my masonry heater I have an external combustion air supply. Highly recommended. The diameter depends on the respective lengths, necessary bends, the output of the heat generator, and the effective chimney height.
I would only consider a wood stove if it is about occasional "fire experiences."
If a sustainable heating energy share is the priority, a wood stove is unsuitable due to the poor efficiency.
In this case, a masonry heater is needed. For example:


Best regards.
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Hi!

We have converted our wood stove in the new house to external combustion air supply. We didn’t want air supply through the floor slab because we didn’t know what might accumulate in the pipe over the years.

The stove contains not 2 pipes, but rather a flue gas pipe and the combustion air supply through the surround stone. As a result
- unfortunately, we don’t have any waste heat from the stove on the upper floor
- the draft is rather weak (but sufficient).

A bend in the air supply should not matter – inside the stove I have several angles. A bend in the flue gas pipe means more soot in places that you cannot clean.

As far as I know, our system is more expensive; it doesn’t seem to be better.

Oh, yes – if you are persistent, you can manage the air supply without visible aluminum pipes.

Best regards,
Tomtom.

Hello,

we had the Universo fireplace from Plewa installed. It has an exhaust pipe in the middle and around the exhaust pipe there is space for the fresh air in the cladding stone.

This system works very well for us. Our stove (Nibe Contura) burns excellently. Can recommend Nibe.

The problem that the exhaust air is sucked back in does not exist for us because the exhaust air rises vertically due to the heat and the fresh air area of the fireplace at the top is covered with a kind of hood that only sucks in the fresh air under the hood.

And that brings me to the explanation of how the fresh air comes down. Due to the heat of the exhaust air, the exhaust air rises in the fireplace. This creates a negative pressure in the stove that causes new air to flow in. The stove draws it from the fresh air shaft. It practically sucks it in. This creates a constant draft in the stove that ensures a clean fire.

Of course, it is also true that this means the fireplace itself does not get warm and the rooms on the upper floors are not heated.

I would build like this again anytime.

Yalta

Hello Yalta! In principle, what you write is exactly right. I am also building a chimney with air supply (Schiedel Absolut). Unfortunately, the air supply does not always work. My stove seller (very experienced) told me to my surprise that many stoves had to have the air supply disconnected again. They did not draw, but started to smoke. Depending on the weather conditions/chimney length, such problems sometimes occur (regardless of the stove model). I want to hope for the best.

Hello Stefanlein,

that surprises me. This is the first time I’m hearing that.

Nevertheless, of course I can only speak from my own experience, and that has been very good with this combination.

We have been heating almost daily with wood since the beginning of October and have never had the problem you described.

However, we must keep in mind that the stove is not yet able to draw the supply air from the chimney during the lighting phase. This only works once there is sufficient draft in the exhaust shaft.

For the lighting phase, we therefore have to leave the stove door ajar so that the stove can easily draw the supply air from the room air. Only when it is burning properly can we close the door, and then the fire is supplied from the supply air shaft.

If you pay attention to this, the fire in the stove burns wonderfully.

With us. With our combination of chimney and stove.

If your stove fitter has different experiences, I can’t say anything about that.

Yalta