Gas Flue and Ventilation Rules: A, B and C Type

Updated: 2026-10-27

Flues and ventilation are where natural gas projects most often get stuck. The rules depend on where an appliance takes combustion air from and sends flue gas to. This guide follows the İGDAŞ 2017 technical principles and notes Samgaz differences.

The ventilation rules (1 m³/kW, 150 cm²) appear with the same wording in all 13 Turkish gas distribution company specifications we reviewed [1]. Some detailed dimensions may vary by company.

Appliance types

The definitions are in İGDAŞ pp. 13 and 47 [2]. A combi boiler is a B, B1 or C type appliance with a rated output not exceeding 70 kW [2].

Room volume and vents (A and B type)

• The room needs at least 1 m³ for every kW of total input [3].
• A type appliances cannot go in a space under 12 m³ [3].
• B type appliances cannot go in a room with a net volume under 8 m³ [3].
• The room has a permanently open vent of at least 150 cm² [3].

If the volume is too small, the room is joined to a neighbouring room [3]:

• Low and high vents of at least 150 cm² each are opened.
• The high vent is at least 1.80 m above the floor.
• The low vent is at most 45 cm above the floor.
• The neighbouring room cannot be a bedroom, bathroom, toilet or common area.

In the Samgaz text the low vent height figure is illegible; confirm it with the company in the Samgaz region [4].

Indirect ventilation: if a vent cannot open directly outside, vents of at least 150 cm² are opened in the door or wall to the neighbouring room and in that room's outside window [5].

35 kW and above: if A and B type appliances total less than 35 kW, 150 cm² is enough. At 35 kW and above, the vent is calculated and the flue gas is removed mechanically [3].

Prohibited locations

A CO detector is mandatory in a room with a B type appliance [6].

B type: flue pipe and chimney

Flue pipe (appliance to chimney):

• Horizontal developed length at most 2.5 m [6].
• A 90° elbow counts as 60 cm, a 135° elbow as 30 cm [6].
• A vertical draught diverter section of at least 20 cm at the appliance outlet [8].
• Samgaz: at least 3° upward slope; avoid 90° elbows [9].

Chimney:

• Flued appliances connect only to an individual chimney; not to a plain masonry or shared (shunt) chimney [10].
• The chimney is vertical and may offset only once, by at most 45° [8].
• No fan or kitchen extractor may be connected to the chimney [8].
• No chimney through a light well under 1 m²; at least 1 m² net must remain after the chimneys are installed [8].
• Stainless steel at least AISI 316L; chimneys outside the building are double-walled [11].
• In a shared air-flue system: at most 30 kW per appliance and 2 appliances per floor [8].

C type (room-sealed) flue outlets

Flue gas must not discharge into [7]:

• Passages, corridors and narrow gaps between eaves
• Ventilation shafts and light wells
• Open or enclosed balconies, lift shafts
• Under projecting parts of the building
• Openings that supply fresh air to other units

There must be at least 3 m to the opposite building in the discharge direction [7]. A room-sealed outlet cannot open into a courtyard enclosed on all four sides and smaller than 200 m² [12].

Additional Samgaz rules [13]:

• At least 2.5 m vertically and 1 m horizontally between flue terminals.
• A C type appliance above 35 kW discharges through a chimney.

Clearances to windows, eaves and corners are given in figures and tables and may vary by company.

Condensing appliances

• The flue connection rises at least 3° from horizontal; 90° elbows are not used [14].
• A condensing appliance taking air from the room follows the B type 1 m³/kW and vent rules; a CO detector is mandatory [14].
• Appliances above 50 kW go only in a dedicated appliance room [14].
• Condensate up to 200 kW may be discharged without neutralisation [14].

Chimney outlets on pitched roofs

Main dimensions from İGDAŞ Figures 20–26 [15]:

• a ≥ 0.4 m relative to the ridge.
• Horizontal distance to the roof surface c ≥ 1.5 m.
• If A < 1.5 m then B ≥ 0.6 m; C ≥ 0.6 m; D ≥ 2 m.
• Obstacle rule: if f < 1.5 × g, then e ≥ 1 m (natural draught) or e ≥ 0.4 m (positive pressure).
• A roof pitched at 20° or less counts as flat.

The letters are defined in the figures; check your drawing against them.

Chimney sizing

• TS EN 13384-1 for a single appliance, TS EN 13384-2 for several (cascade, air-flue systems) [16].
• Installation to TS EN 15287-1+A1 and TS EN 15287-2 [16].
• Minimum draught 4 Pa for negative pressure flues; wind pressure PL = 0 may be assumed [16].
• A circular section is preferred [16].

Samgaz states that a software calculation is accepted and lists the inputs: appliance type, fuel, flue gas mass flow, minimum flue gas temperature, draught, CO₂ and outlet size [17].

How to do it with GazPlan

In GazPlan you draw the room with the room tool and enter its ceiling height and vent. The appliance type (A/B/C) and flue pipe length are entered in the appliance panel. "Check" reviews the 12 m³ / 8 m³ / 1 m³/kW rules, the 150 cm² vent, the 35 kW warning, whether a B type appliance is connected to a chimney and the 2.5 m flue pipe. A chimney checklist lets you tick off the specification clauses. GazPlan does not size the chimney; enter the TS EN 13384 result from your chimney software.

• Open the program
• Room volume and vent calculators
• Distribution companies

For how these rules apply when changing a boiler, see is a project required for boiler replacement.

This guide is for information only; projects are prepared by a certified engineer and the distribution company's current specification prevails.

Sources

1. GazPlan specification comparison (13 Turkish gas distribution company specifications), 2026, section 3.
2. İGDAŞ Doğal Gaz İç Tesisat Teknik Esasları (Technical Principles) 2017, pp. 13, 47.
3. İGDAŞ 2017, p. 36.
4. SAMGAZ İç Tesisat Şartnamesi (Internal Installation Specification), Rev. 2019.03, p. 116.
5. İGDAŞ 2017, p. 35.
6. İGDAŞ 2017, pp. 36–37.
7. İGDAŞ 2017, pp. 39–40.
8. İGDAŞ 2017, p. 56.
9. Samgaz Rev. 2019.03, p. 135.
10. İGDAŞ 2017, p. 54.
11. İGDAŞ 2017, pp. 56–57.
12. İGDAŞ 2017, p. 30.
13. Samgaz Rev. 2019.03, p. 131.
14. İGDAŞ 2017, pp. 41–42.
15. İGDAŞ 2017, pp. 37–39 (Figures 20–26).
16. İGDAŞ 2017, pp. 56–58.
17. Samgaz Rev. 2019.03, pp. 198–199.