Which material should be used to cover the wall behind the stove with?

[Poosen]

I am going to install a brand new freestanding wood-burning stove that will be connected to a steel flue that was previously used for an oil furnace. The pipe is insulated all around and runs inside a plastered shaft in an existing interior wall. At the hole I have made in the wall where the stove will be connected to the flue behind the stove, I have removed the tongue-and-groove board that was directly under the surface layer of the wall (plaster) and between the tongue-and-groove board and the existing plaster shaft, there was a 5cm wide air gap.
What I'm wondering now is what I should use to cover behind the stove. Should it be minerit or is fire-resistant plasterboard sufficient? The idea is to have tiles on the outside. Should the air gap remain, or should I fill it with insulation? On the floor, the plan is to have a glass panel from the stove manufacturer.

 

[Erik321]

Calcium silicate board is available in both 25mm and 50mm thickness.

 

[Claes Sörmland]

It depends on how much the stove radiates in terms of IR in each direction and the distance it stands from the wall. Since it varies greatly between stoves, the requirements are in the installation description that comes with the stove.

If there is a requirement for a fire wall, it is traditionally a brick wall. Today, there are panel solutions that are thinner and based on air passing behind a fireproof panel to cool it. Another variant is to build a wall with two fireproof panels with rock wool in between as thermal insulation.

 

[Poosen]

Calcium silicate board is available in both 25mm and 50mm thicknesses.

That might be an option if I place a 50mm board inside the air gap that is between the plasterboard shaft and the inner wall. This way, it won't extend too much from the rest of the wall.

 

[Poosen]

It depends on how much the stove radiates in the form of IR in each direction and the distance it is from the wall. Since it varies greatly between stoves, the requirements are stated in the installation description that comes with the stove.

If there are requirements for firewalls, it is traditionally a brick wall. There are panel solutions today that are thinner and work by allowing air to pass behind a fireproof panel so that it is cooled. Another variant is to build a wall with two fireproof panels with stone wool in between as thermal insulation.

The stove should be at least 10 cm from the combustible wall behind it according to the instructions. It will be, and then I interpret it as theoretically acceptable to have a regular gypsum wall behind if there was a freestanding flue going out from the top? But now the pipe is going to exit the back of the stove and go straight into the wall. I should then (I think) need some non-combustible material immediately around the pipe penetration through the wall. Plus a few cm gap/air space around the pipe that I will insulate with some type of insulation mat?

 

[ramafred]

Have you spoken to the chimney sweep who will do the inspection later?

If you pose the question with a few different solutions, they can usually point out what is most correct.

 

[Claes Sörmland]

The stove should be at least 10cm from the combustible rear wall according to the instructions. It will be, and then I interpret it as theoretically possible to have a regular gypsum wall behind if it were a freestanding flue out from the top? But now the pipe is going to exit from the back of the stove and straight into the wall. I should then (I think) need some non-combustible material immediately around the pipe penetration through the wall. Plus a few cm gap/air space around the pipe that I will insulate with some type of insulating mat?

I think you're absolutely right. You need to build a shaft through the wall that can withstand the heat radiation from the flue pipe. Typically, you buy an approved flue pipe, and its instruction manual will state how this shaft should be designed.