Fireplace kit - New construction - Load-bearing insulation

Hello everyone,

in our new building, we would like to address the topic of a fireplace, and we would appreciate your opinions and experiences.

The following situation applies:

[*]LAS chimney from the company Erlus TYPE SL 18 (11m total length, 18 cm diameter).
[*]Location: living room, open kitchen, approximately 50 sqm in total, open stairwell up to the 2nd floor.
[*]Plan: room air-independent fireplace kit, such as Camina S9, weight approx. 500kg.

[*]KfW-40, triple glazing, residential ventilation without heat recovery, controlled by a fan in the attic.

We would like your opinions on the following points:

[*]At the location where the fireplace will later stand, a recess in the screed will be made. However, this will not be filled with bonded screed, as is normally the case. According to the architect, the reason is that a thermal bridge would then arise and therefore bonded screed cannot be used. Instead, Styrodur will be used there as pressure-resistant insulation. The architect’s statement is "up to approx. 1000kg is not a problem." What experiences have you had here? What do you think? What should be considered?

[*]Topic "air pressure monitor": Probably only the responsible district chimney sweep can give us a statement on whether we need this, correct?
[*]Is it possible to tile over the expansion joints between "normal" screed and the screed recess? Can we choose a large screed recess and possibly tile over it if the fireplace footprint turns out to be significantly smaller?

[*]What else should we pay attention to when you read about the project like this?

Thank you for your support.

Best regards,
Sebastian

Hello,

- Styrodur + sufficiently strong screed on top for load distribution should be enough. Whole houses stand on Styrodur.

- Include BzSfm from the beginning, especially with self-build kits. Not only controlled ventilation, but also a kitchen extractor hood with exhaust must be considered. Keyword window contact.

- Do not tile over the expansion joint, but make the joint visible in the tile pattern again. In front of the fireplace, you need a fireproof surface made of tiles, glass, or similar anyway.

Also important:
The fireplace should emit as little heat directly into the air as possible. KfW40 is so well insulated that even this large surface quickly overheats. The Camina S9 has a nominal output of 7 kW and a panoramic glass panel. That sends a lot of heat directly into the room.... I would choose a fireplace with a normal glass panel and even more thermal mass. Especially the 7 kW... well, they are. I have pushed my 14 kW (11 water, 4 air/stone) up to 16 kW into the water alone. So much for the 7 kW. Your whole house will probably have a primary energy demand below 7 kW!

Hello,

Thank you for the answer, it has already been very helpful. I am curious to see if any further good suggestions will arise here.

However, the answer raises further questions:

a) Regarding the 7kw: We like the Camina S9 visually very much. Apart from the possibility that it might be oversized and therefore might get too warm too quickly and we might not heat it fully, are there any other disadvantages?

b) Regarding the screed recess: The Camina S9 has a base area of 730 x 730 mm. The required screed recess is specified as 701 x 672 mm. I interpret this to mean that the load-bearing parts (701x672) are extended by the optical parts (730x730). One could nicely tile underneath there. Would you have the screed recess cut exactly to 701x672 mm or leave some buffer (e.g. 10 cm) to have some leeway for possible "errors"? Even if you take a 20 cm buffer, the expansion joint of the optical parts would still have to be covered. And even if not, through appropriate tiling, see above, that could also be covered. Why do I ask? - If we take the specified screed recess and for whatever reason, there is even a 1 mm difference on one side, the fireplace kit can no longer be used because the recess is too small. What speaks against making a screed recess of 720 x 720 mm?

Best regards,
Sebastian

General: our chimney sweep asked about everything that actively exhausts air on the floor of the fireplace: extractor hood, controlled residential ventilation, forced ventilator in the bathroom

Pay attention to the necessary distances from combustible components. For example, 80 cm between glass panes and wooden walls, wooden door frames, etc. (you can possibly also measure from the middle of the combustion chamber, but you should clarify this with the chimney sweep beforehand)

We also thought for a long time about whether to just leave something out and ultimately decided to do the fireplace right away because of the screed issue...

Ok, so it won't be set in the classic way...
We have a chimney set in the classic way and have thinned the screed on the floor slab in front. 1mm from it is nothing, the tolerance in the screed area is greater
If it is to be the chimney, I would build the recess exactly to the max. Around it, you have about 1cm of edge insulation strip anyway.

Regarding stove power: You don't reasonably operate a wood stove at 40 or 50% of its power. The fire must burn with a long flame, otherwise there will be glossy soot and the stove will become coated with tar.

We have assembled a kit weighing 1.1 tons. It was placed on the continuous floor covering or screed, so we have no special insulation under the area and no expansion joint either. So far, it is working.