ᐅ Combustion Air Supply / Wood Stove – Thermo-Air Draft or Floor Slab

Hello community,

In the next few days, we will need to decide how to manage the fresh air supply for the wood-burning stove planned for our yet-to-be-built single-family home without a basement, built to KfW 55 standard.

Currently, a single-flue chimney with a thermal air supply (from Schiedel) is planned. The stove will be installed against an exterior wall. Stove installers frequently point out that supplying combustion air through a thermal air duct is not ideal and that using an intake through the floor slab would provide better results and could also save money.

Now we are wondering if this might cause problems that we actually want to avoid. Also, replacing the stove later could be complicated since the new one would have to have the exact same dimensions if the fresh air comes through a floor connection, right?

After already having to accept that we will need a pressure monitor, the fresh air supply issue is making us a bit uneasy. At times, we are even considering abandoning the whole stove idea. After all, we do have a heating system.

What are your opinions on these two fresh air supply options?

Regards

Hello, our architect also advised us to install a fresh air duct above the floor slab. In fact, a wall opening with a closable flap is planned.

I would avoid going through the ground slab. Technically, it’s not that straightforward because of drainage, condensation, and so on. Can’t you build a two-flue chimney instead?

Cruiseaddict schrieb:
Currently planned is a single-flue chimney with a thermal air draft (from Schiedel)

We will only be connecting a wood-burning stove, so a single-flue chimney is sufficient. The chimney also includes a thermal air draft. However, stove installers usually do not prefer this. They tend to favor air supply through the floor slab. Besides the potential issues with condensation-related damage, we would then be permanently tied to the same wood stove because there would be a hole in the floor, right? That is the main obstacle for us.

Thermal air draft in the chimney, air supply through the floor slab, or simply omitting all this, which would also mean we could avoid the chimney sweep visit and associated costs?

My question was actually this: If the stove fitter, for whatever reason, doesn’t like a "thermal air flue," why don’t you build a chimney with two flues—one for combustion air and one for the exhaust gases? Or what exactly is the problem that stove fitters have with this "thermal air flue"? I can’t quite understand it.

Of course, the best option is to do without a chimney and stove altogether. It costs around 10,000 euros (about 11,000 USD) in total, and no one really needs it. But I wasn’t able to avoid it either.

Our chimney installer recommended a LAS chimney flue for the new build. As mentioned before, this is a chimney with a "double pipe." Reasons:

When air enters through the base slab, it creates a kind of draft due to air exchange. This is usually prevented by a pressure flap installed in the wall at the fresh air inlet.

The air coming through the base slab is much colder in winter, which can lead to condensation forming below the combustion chamber. This can negatively affect the chimney’s lifespan.

With a double pipe, the fresh air is warmed by the exhaust gases during the combustion process. The chimney essentially draws air on its own due to the thermodynamics involved.

In the end, the double-flue chimney costs a bit more but is the better option!