What Is the 15 °C Minimum Heating Limit in Central Heating Systems?

Where Does the 15 °C Limit Come From?

The provision is part of the Turkish Regulation on the Allocation of Heating and Domestic Hot Water Costs in Central Heating and Domestic Hot Water Systems, published in the Official Gazette of 14 April 2008 (No. 26847, repeated issue). Under Article 5, paragraph 6 of the regulation, room temperatures in apartments heated by central systems are set to at least 15 °C.

The preceding paragraph of the same article requires thermostatic radiator valves conforming to TS EN 215 in centrally heated buildings so that energy consumption can be limited. In other words, users can turn their rooms down as they wish with thermostatic valves, but the regulation requires that an apartment’s temperature not be set below 15 °C.

What 15 °C Means and What It Does Not

• It is a lower limit, not a comfort temperature. 15 °C does not mean the apartment must be kept at a comfortable living temperature; it is the lowest value that should not be undercut even in rooms where heating is turned down or not used at all.
• It is not a penalty. Its purpose is not to punish the user but to prevent damage to the building, the heating system and neighboring apartments.
• Meters do not enforce this limit. Heat meters and heat cost allocators do not regulate room temperature; they measure the heat consumed or the share of heat. 15 °C is a rule about how the system and the valves are set.

Why Heat Balance Between Neighbors Matters

In a centrally heated building, apartments are connected to each other by walls, floors and ceilings. An apartment whose heating is shut off completely keeps drawing heat from the neighbors below, above and beside it as it cools down. The extra heat the neighbors use to make up for this loss is recorded on their meters, while the user of the cold apartment benefits from that heat without contributing to its cost. The result is an unbalanced and unfair distribution of costs.

Here the 15 °C limit acts as a buffer temperature between neighbors. The aim is not to restrict individual freedom of use but to protect the operation of the central system as a whole.

Why the 15 °C Limit Matters

• Protecting the building: Reduces the risk of condensation, damp and mold on cold surfaces.
• System safety: Reduces the risk of pipes and radiators freezing in cold weather.
• Neighboring apartments: Limits how much one apartment’s heat loss adds to the load of the others.
• System balance: Helps the central heating system run more steadily.

How It Affects Heating Cost Allocation

Under Article 8 of the same regulation, the total heating cost in central heating systems is allocated as follows:

• 70% according to the measured heat consumption of the apartments,
• 30% as the heat cost arising from common areas, system losses, minimum heating and operating costs, according to the floor area of the apartments

is shared out. In district heating systems this common share is 20%. The regulation does not define a separate item or formula for minimum heating; this cost is counted within the common share that each apartment pays in proportion to its area. That is why an apartment that does not use heating at all still pays the common share: it benefits from the building’s common heat and from the heat coming from neighboring apartments.

For all steps of the allocation, see our How Are Central Heating Costs Allocated? guide.

Minimum consumption calculation in practice

Some buildings add an extra step to their allocation rules: apartments whose measured consumption is far below the heat needed to keep the apartment at around 15 °C are charged a minimum consumption. In one such method, the building’s average consumption per square meter is multiplied by a factor set according to the climate zone and the month; the result is multiplied by the apartment’s area to give the minimum consumption. If the apartment’s measured consumption is below this value, the minimum consumption is used in the calculation.

This calculation is not set out as a formula in the regulation; whether it is applied and what factors are used are determined by the building’s allocation rules. Since the factors vary by region and month, 15 °C on its own is not a quantity of consumption but the lower-limit reference on which this calculation is based. Whether units such as shops, empty apartments or commercial units are excluded from the calculation is also determined by the same rules. In our heat cost allocation service, minimum heating is applied building by building, as the management prefers. You can find out how it is applied in your building from your cost allocation statement or from your building management.

How the 15 °C Limit Is Maintained in the System

Heat meters and heat cost allocators measure consumption; they do not regulate temperature. Maintaining the limit depends on the system being installed and balanced correctly:

• Hydraulic balance: Manifolds with flow meters and balancing valves make sure each apartment and circuit receives its design flow. In an unbalanced system some apartments do not heat enough even when the boiler is running. For details, see our What Does a Manifold with Flow Meters Do? page.
• Thermostatic radiator valves: Valves conforming to TS EN 215, as required by the regulation, limit consumption by controlling the room temperature.
• Metering: In apartments supplied by a single line at the apartment inlet, consumption is measured with a heat meter (What Is a Heat Meter?). In buildings where radiators are fed from separate risers, a heat cost allocator is fitted to each radiator (How to Read a Heat Cost Allocator). Without accurate metering, neither the 70% consumption share nor the minimum heating calculation can be done properly.