Is a Gas Project Required for Boiler Replacement?

Updated: 2026-10-27

Short answer: none of the specifications we reviewed has a clause titled "boiler replacement" that says a project is or is not required. The clauses we found deal with alteration, additional and supplementary projects. So for a definite decision, ask the gas distribution company in your region.

This guide sets out what the sources say explicitly and which rules a boiler replacement may affect. It does not give a ruling; it shows what to look at.

What do the specifications say explicitly?

These clauses use the idea of "altering the installation". Whether fitting an appliance of the same type and output in the same place counts as an alteration is not defined in the documents. That line is drawn by the distribution company.

The 0.8 mbar limit for additional projects is the same in the Esgaz, Palen, Palgaz, Torosgaz, Doğugaz and Kırgaz documents [5].

Which changes affect the installation?

Whether or not a project is required, the existing installation should be checked against the new boiler in the following cases.

1. Higher output and flow

• The minimum flow for a combi boiler is 2.5 m³/h; a larger boiler's flow is calculated [6].
• Flow = capacity (kcal/h) / 8250. Below 70 kW, efficiency is ignored [6].
• Example: 24 kW ≈ 2.5 m³/h; 30 kW ≈ 3.1 m³/h (30 × 860 / 8250).
• The meter-to-appliance loss must not exceed 0.8 mbar [2].
• If the flat's total flow exceeds 5 m³/h, the excess is added to the flat and riser flows [7]. The riser calculation may then be affected.
• Check the meter too: a G4 meter's upper limit at 21 mbar is 6 m³/h [8].

For the method, see the natural gas pipe sizing calculation guide.

2. Change of appliance type (flued to room-sealed)

• B type (flued) appliance: at least 1 m³ of room volume per kW, a net volume of at least 8 m³, a permanently open vent of at least 150 cm² and a CO detector [9].
• C type (room-sealed) appliance: no volume or ventilation limit [10].
• A C type flue must not discharge into passages, corridors, light wells, balconies, lift shafts or under projections [10].
• There must be at least 3 m to the opposite building in the discharge direction [10].
• In Samgaz, a C type appliance above 35 kW discharges through a chimney; discharge through an outside wall needs company approval [11].

3. Switching to a condensing boiler

• The flue connection rises at least 3° from horizontal; 90° elbows are not used [12].
• Stainless steel is at least AISI 316L [12].
• Condensate up to 200 kW may be discharged without neutralisation [12].
• A condensing appliance above 50 kW goes only in a dedicated appliance room [12].

4. Moving the boiler

• A B type appliance cannot go in a bedroom, bathroom, toilet, open balcony, stairwell or light well [9].
• A C type appliance cannot go in a stairwell, common corridor, on a chimney wall or in a light well [10].
• A new location means a new pipe length and new elbows. The pressure drop has to be recalculated.

5. Connected to a shared air-flue system

• Each appliance on such a system may be at most 30 kW, with at most 2 appliances per floor [13].
• A more powerful boiler may exceed this limit.

6. Connection details

• There is a shut-off valve at the appliance inlet [14].
• A combi boiler's flexible connection hose is at most 60 cm [14].
• For a flued boiler, the horizontal flue length is at most 2.5 m; a 90° elbow counts as 60 cm [15].

Differences between companies

• The 0.8 mbar meter-to-appliance limit at 21 mbar is the same in all sources reviewed [5].
• The efficiency rule differs: İGDAŞ and Torosgaz say "no efficiency below 70 kW", while some companies apply 90% to appliances not in the catalogue [5].
• Some appliance and room details (vent heights, cabinet sizes) are illegible in certain documents. These values may vary by distribution company.

A practical approach

1. Write down the output, type (B / C / condensing) and location of the old and new boilers.
2. Mark which of the items above change.
3. Ask the distribution company or a certified installation firm, with this information to hand.
4. If a project is required, photograph the existing installation; the remote site survey with photos guide covers this step.

How to do it with GazPlan

In GazPlan you can draw the existing flat and pick the new boiler from the product list or by its kW rating. The program calculates the appliance flow, checks the meter-to-appliance loss and velocity, and suggests the meter size. The "Check" button reviews appliance type, room volume, vent and flue length rules. You get a concrete calculation to bring to your distribution company.

• Open the program
• Boiler flow and pressure drop calculators
• Find your distribution company

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

Sources

1. İGDAŞ Doğal Gaz İç Tesisat Teknik Esasları (Technical Principles) 2017, p. 58.
2. İGDAŞ 2017, p. 20.
3. SAMGAZ İç Tesisat Şartnamesi (Internal Installation Specification), Rev. 2019.03, p. 225.
4. Samgaz Rev. 2019.03, p. 199.
5. GazPlan specification comparison (13 Turkish gas distribution company specifications), 2026, sections 2–4.
6. İGDAŞ 2017, pp. 17–18 (Table 4).
7. İGDAŞ 2017, p. 20.
8. İGDAŞ 2017, p. 33 (Table 17).
9. İGDAŞ 2017, pp. 36–37.
10. İGDAŞ 2017, pp. 39–40.
11. Samgaz Rev. 2019.03, p. 131.
12. İGDAŞ 2017, pp. 41–42.
13. İGDAŞ 2017, p. 56.
14. İGDAŞ 2017, p. 35.
15. İGDAŞ 2017, pp. 37, 56.