- Flue is free-standing construction. Therefore, it is not admissible to connect flue to the construction of building, therefore, free gap of 5 up to 10 mm between it and flue shall be left – Fig.5
- Flue shall not directly be in touch with combustible surfaces of walls. Therefore, at least 5 cm indention shall be kept, but it shall be allowed to circulate air in the free space. – Fig.6
- Dilatation at the exit of flue through ceiling shall be:
- if ceiling is fireproof 3 cm – Fig.7.a
- if ceiling is combustible 5 cm – Fig.7.b
Free space shall be filled with fireproof insulation 
- Passage of chimney flue through combustible wall shall be protected in radius of at least 15 cm with fireproof material – e.g., fireproof insulation – Fig.8.a Passage of chimney flue through fireproof wall shall be insulated in entire length, in order to avoid thermal stress – Fig.8.b
- When connecting chimney flue with ceramic connection T-piece of flue, reserve for dilatation shall be observed mandatorily:
- for gas and oil boilers with low temperature flue gases, dilatation gap shall be about 3 mm, but it can be filled with special, fireproof cord or also with flexible, fireproof silicon.
- for solid fuel boilers, dilatation gap shall be 5 – 10 mm, but it can be filled with special, fireproof cord – Fig. 8a and 8b.
- for classical fireplaces and fireplace furnaces, dilatation gap shall be 5 – 10 mm, but it can be filled with special, fireproof cord. It is recommended to use connection T-piece 45° in this case – Fig. 9
Before the insertion of the chimney flue into connection T-piece, the entering end of it shall be reeled with fireproof cord. The recommended dimensions of the cord are given in Table 1.
| Fireproof cord | Length of cord assuming that 4 turns are reeled | Length of cord assuming that 4 turns are reeled | Length of cord assuming that 4 turns are reeled | Length of cord assuming that 4 turns are reeled |
|---|---|---|---|---|
| D 14 | D 16 | D 18 | D 20 | |
| Ø 6 mm | 1,72 m | 2,00 m | 2,28 m | 2,56 m |
| Ø 10 mm | 1,68 m | 1,96 m | 2,24 m | 2,25 m |
ATTENTION!
Sometimes there are situations, when during the stage of completion of construction works, it is necessary to connect provisional heating equipment for the purpose of warming of rooms. In such case, it shall be followed that length of chimney flue is sufficient to avoid direct contact of connection T-piece with flame. Connection of heating equipment of such type with overly short chimney flue sections may facilitate the thermal shock and lead to damages (flawing) of connection T-piece.