Wood burner chimneys

I would start with the urbanisme department of your local commune. These will cover the "design" aspects of the chimney, such as where it can go on a building etc, and will likely vary according to what commune you are in.

There may be other rules covering emissions etc. which may be regional or federal.

Otherwise the obvious route would be to ask a company like Stuv who manufacture wood burning stoves and are based in Wallonia.

This page https://energie.wallonie.be/fr/les-cheminees-un-element-determinant.html... gives the basics (for all uses of chimneys). Note that the precise requirement for the chimney depends on the type (and size) of the wood-burning stove that you intend to install. If you are installing a new stove in an existing building, the stove retailer will tell you the type(s) of stove (and the size you require for the space you intend to heat) and tell you what has to be done to the chimney to enable the stove's installation. (It might mean the installation of a new external stainless steel chimney if that is practical.) Obviously you can ask several retailers to quote (three is the norm), it is unlikely that you will be able to install a modern stove without some alterations to an existing chimney.
Finally, don't forget that the chimney has to be swept annually (and failure to do so will invalidate your insurance policy), so ensure that provision is included to make that task as easy as possible.

If you have a fire and you can't prove you've had the chimney swept by a "pro", you won't get any insurance money. It's not just for wood stoves, it's for flues from central heating installations as well.

Yes, agree with the others above, you should be careful to ensure that you comply with any small print in your insurance policy. Most will state that you need to have your chimney swept annually.

You probably haven't seen any chimney sweeps "down here very much" as they don't wander about door to door looking like Dick van Dyke out of Mary Poppins, they are typically wearing nice overalls and are the engineers that service your central heating every year.

Also - if you're adding a new chimney (as opposed to using an existing one) you will be altering the external appearance of the house, and will almost certainly need planning permission from your commune.

Most people have their chimney(s) swept when they have their central heating boiler serviced which (at least if it uses mazout) has to be serviced once a year too - by law.

Don't forget to install a smoke alarm, fire alarm and carbon monoxide alarm.

It costs €50-60 to get your chimney swept. Do it.
If your chimney and house should catch fire, the consequences do not bear thinking about! It's a no brainer.

please work only with 'agrées' qualified companies for planning and installation. This matter is too serious as the above comments show!