Smoke is usually caused by a lack of draft in the chimney. Your tiled stove/tiled fireplace may be supplied with an insufficient amount of combustion air. Therefore always open the combustion air lever completely when heating up. The combustion air is only reduced as soon as the wood burns properly. The reason may also be a lack of draft, often due to a cool air column in the chimney. This column is often generated in the transitional periods in spring or autumn on sunny days. The air in the chimney is then colder (i.e. heavier) than the air in the open. This leads to a lack of negative pressure in the chimney, it doesn’t draft. Here a little trick: you open the chimney door, burn a sheet of newspaper there or in the combustion chamber and this way heat the air column directly. The heating gives the chimney its natural lift (draft). Congested flue gas outlets may also be the cause of draft problems and smoke nuisance. Please also pay attention to a regular maintenance of your tiled stoves/tiled fireplace by a specialized company. All combustion processes produce residues in form of soot and ash particles which may of course stain a windowpane. However, modern heating inserts are equipped with an integrated window rinsing system which minimizes the contamination of the window. The reasons why the window could still become dirty are as follows: the quality of the combustible. Did you burn anything which must not be put into the tiled stove/tiled fireplace? Is the wood possibly too wet? The tiled stove/tiled fireplace shall exclusively be filled with clean well-seasoned wood. The wood’s residual moisture should be less than 20%. This is achieved by storing the wood for 2 to 3 years. An incomplete combustion will also increase the sooting of the window. Pay attention to an adequate supply of combustion air and check the chimney’s draft. Your chimney sweep is a competent advisor in this regard.