At least two conditions are always checked: the pressure or negative pressure conditions and the temperature conditions. If the exhaust system's pressure is not high enough, the exhaust gases may not be safely discharged to the outside. Checking the temperature conditions ensures that no long-term damage occurs due to condensation and that the chimney does not freeze in low outside temperatures. Ultimately, the result of the calculation tells you whether, for example, a particular fireplace can be operated with an existing chimney or whether a new chimney is suitable for an existing fireplace.

Chimney calculations therefore serve to plan heating systems correctly from the outset and avoid mistakes that can only be corrected later at great expense or, in the worst case, impossible at all. For example, what do you do if the chimney and fireplace are already installed and the chimney sweep tells you during the inspection that your chimney's cross-section is too small?

Dispose of the fireplace and buy a new one, or demolish the chimney? Neither of these options is ideal, and easily avoided by calculating the chimney size in advance.