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Learn about heating control algorithms


From the text you will learn how heating control algorithms work. Also, you will find out which algorithm works best for which type of heating. Moreover, we will present selected models of SALUS Controls thermostats.

Temperature thermostats – what controls the heating?

Heating control algorithms is nothing more than a heating scheme built in the temperature thermostat. It is responsible for maintaining the desired temperature in the room. It decides about effectiveness and functionality of the device. Accuracy of the algorithm results in precise heating control and consequently in lower bills and user’s satisfaction.

How to control heating economically? What is the difference between a simple and a technologically advanced control algorithm? Which one will work best to control radiators and which one to control underfloor heating?

Heating control algorithms are mathematics

Radiator (convection) heating is characterized by fast heating of radiators to high temperatures. Also by consequently fast warming up of rooms (from several to several dozen minutes). Similarly in the opposite direction – fast cooling of radiators and rooms. On the other hand, floor heating is characterized by low heating surface temperature. Also, it is characterized by high thermal inertia (long heating up and cooling down time – up to several hours).

Not every control program is suitable for every type of heating. In order to choose the most suitable control system for your home, it is worth to be aware of that.

CH hysteresis

This is the simplest two-position algorithm (on/off). The thermostat, after reaching the temperature set by the user, sends the heating demand signal to the boiler again. It causes constant temperature oscillation – heating up, cooling down, heating up, cooling down, etc. If the hysteresis is set at ± 0.5 degrees Celsius, and the demand value is 23 degrees, the thermostat will start the boiler. When the temperature drops to 22.5 degrees, and turn it off when it rises to 23.5. This scheme is based on slight overdriving, and does not guarantee precision. Due to the high inertia of underfloor heating, hysteresis is not recommended in thermostats designed for underfloor heating. It gives more satisfactory results in radiator heating.


A more stable solution is pulse-width modulation control, or Pulse-Width Modulation. This is also a two-position mechanism (on/off), but it includes heating time as an additional parameter. In PWM, the difference between the set temperature and the current temperature determines how long the heating device will run. This is done based on a set table of formulas. For better understanding, let’s transfer this mechanism into a rule. To maintain the set temperature, if the temperature difference is X degrees – the heating device will turn on for Y minutes.. A small difference means short heating, a big difference – long (different rooms heat up in different time). This algorithm is used to control the underfloor heating system with good results.


For TPI (Time Proporcional and Integral), a self-learning time-proportional integral algorithm, the situation is similar to PWM. However, this program does not work based on formulas. It is more efficient because it calculates the furnace run time on the fly, based on mathematical integrals. It „learns” instead of using templates. The thermostat „knows” how long the furnace has to be turned on to reach the desired temperature at the appointed time. The thermostat „predicts”: when the temperature is about to drop, it starts heating early enough. Faster response time in steady states and reduced override result in better control results.

Diagram of Hysteresis, TPI and PWM according to temperature


Internal Temperature Load Compensation is a high-tech precision temperature maintenance algorithm that can be described as the new TPI. It is more accurate and provides even better control over heating.

Heating control with SALUS Controls thermostats

SALUS Controls company offers temperature thermostats suitable for all types of heating. In comparison with other brands it comes out better in terms of matching the control algorithm to the type of heating. For example, models dedicated to floor heating are equipped with ITLC / TPI or PWM algorithms (not limited to hysteresis). So, SALUS Controls company has developed and proved in operation also more precise algorithms than PWM.

Each system should be considered individually. Although, let’s assume that radiator installations can be handled by standard models. As well as those from SALUS Smart Home wireless series. For underfloor heating – the best choice are products from the Expert HTR, Expert NSB and Expert lines.


Digital, wired temperature thermostat (flush mounted model – installation in φ 60 mm box). It has PWM system and ability to create schedules. It is used to control surface heating or cooling (e.g. underfloor heating). Through a wiring centre, the thermostat influences the economical operation of daytime thermostats (night-time temperature reduction – NSB). It cooperates with KL08NSB or KL06-M (230V) and NC or NO type actuators.


Digital battery-powered thermostat with TPI heating algorithm and an input for an additional sensor of floor/air temperature. It is used for wireless control of SALUS Smart Home devices (KL08RF wiring centre , TRV head, RX10RF control module). Device can be controlled offline (with the CO10RF coordinator – then it works as a weekly controller) and online (using the Internet gateway UGE600 and SALUS Smart Home application). It provides the ability to create your own schedules.


Digital temperature thermostat with TPI heating algorithm. Device has an input for an additional temperature sensor (floor/air) or occupancy sensor (hotel card). Device is used for wireless control of SALUS Smart Home devices (KL08RF wiring centre, TRV head, RX10RF control module). It can be controlled offline with CO10RF coordinator (or with RX10RF) and online (using UGE600 gateway and SALUS Smart Home application). It gives you the ability to create your own schedules.

Quantum SQ610

Multifunctional temperature thermostat controlling SALUS Smart Home series products. Provides an option to control offline (via CO10RF), online (via UGE600 and mobile app) and wired (with direct connection to the devices like wired wiring centre, boiler). Among the many advantages of Quantum SQ610 the most noteworthy are:

VS30W, SQ610, VS20BRF, HTRP-RF(50)

Finally, Quantum model is equipped also with an optimization feature based on the ITLC algorithm – OPTIMUM START / OPTIMUM STOP.

What are heating control algorithms about?

Better control precision and increased scheduling accuracy. When the OPTIMUM START function is enabled, the thermostat sends a heating signal to the heat source well in advance. As a result, the temperature set for the room is reached at the set time. On the other hand, when the OPTIMUM STOP function is enabled, the thermostat will act in the opposite way. It will calculate the system inertia (cooling down time). Then it switches off the heat source in advance in order to lower the temperature in the room . As a result, without sacrificing comfort and while maintaining the temperature set in the schedule, we avoid overdriving. It is convenient and economical.

OPTIMUM START and OPTIMUM STOP are optional. They can be switched on or off. Energy-saving additions make the temperature thermostat even more effective.

As you can see, modern thermostats SALUS Controls give the option to choose the control algorithm. The range of products is rich. Depending on the budget and user needs, everyone will find something for themselves.

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