Cosa Smart Room Thermostat 
2015–2016 Energy Saving and Combi Boiler Usage Habits Report

Nuvia Smart Energy Technologies
January 2017

This report was prepared by Nuvia Enerji Teknolojileri San. ve Tic. A.Ş. as a result of analysis and calculations made by anonymization of the data obtained from the houses where the Cosa Smart Room Thermostat developed in İTÜ ARI 6 Energy Technopolis with the support of TÜBİTAK.


This report was prepared by analyzing and calculating the anonymized data obtained from the houses using the Cosa Smart Room Thermostat, which was designed and manufactured in Turkey by Nuvia Enerji Teknolojileri San. ve Tic. A.Ş. and launched in December 2014. Within the scope of the report, the combi boiler use habits were determined according to the information obtained from the research conducted with Cosa users.

Nuvia Energy Technologies was established in 2013 in Istanbul Technical University Energy Technopolis to develop convenient, cost-effective, comfortable and economical control systems. Following its establishment, Nuvia has carried out R & D studies rapidly with the support of TÜBİTAK, developed its first product in December of 2014 with its design and production made 100% in Turkey, and brought Turkey’s first smart room thermostat Cosa to the first group of users. Having reached thousands of users all over Turkey in a short period of time, Cosa has made a reduction in natural gas bills starting from the first months of its use. When the anonymized data set of Cosa users from all of Turkey was examined between November 2015 and February 2015, the average natural gas consumption for heating purposes of Cosa users was found to be 31% lower on average than all other combi boiler users. This saving rate varies depending on the city, combi boiler use habits of the users, physical characteristics of the houses, specifications of the natural gas installations and the climatic conditions.

On the other hand, survey studies with Cosa users have found that more than 80% of users have saved on their bills, and more than 90% are extremely satisfied with the product. Another important point is that although a large majority of Cosa buyers did know what a thermostat was before, only 25% had previously owned a thermostat. This indicates that even users who are aware of thermostats do not prefer to use them because of a lack of legal necessity, therefore natural gas is being consumed inefficiently in the houses with combi boilers.

With this report, it is demonstrated by numerical data that in our country with approximately ten million combi boilers, all of which are fully dependent on natural gas, the use of smart room thermostats can save on the natural gas consumption in houses by rates up to one-third, and that there is a saving potential of about 4 billion TL in case the thermostat use spreads country-wide, whereas 6.3 million tons of CO2 emission could be prevented.


As is well known, Turkey is among the few countries where energy dependency is at its highest. Particularly in terms of import figures of natural gas use, it is ranked as the 5th in the world ranking [1]. According to the data of year 2015, a total of 48.427 million Sm3 of natural gas was imported. In contrast, only 387 million Sm3 of natural gas was produced in 2015. On a sectoral basis, about 40% of the imported gas was consumed in electricity generation processes, 29% in industry sector and about one-fourth in housing [2] (Figure 1).

In housing industry, which holds a very important ratio, about one fourth, of the consumption, it is possible to save natural gas at a higher rate with much lower investment costs than the energy and industry sectors. Considering that using a conventional thermostat in about 10 million houses with combi boilers would achieve a saving by 5% to 15%, it could be seen that the use of thermostats with investment costs between 100 and 1000 TL can significantly save energy for our country, which is dependent on gas of foreign origin, and thus reduce our dependency on foreign sources in natural gas [3]. On the other hand, according to the report published in 2003 by EPA (Environmental Protection Agency) within the scope of the Energy Star program, 10 to 30% energy savings can be achieved with programmable thermostats [4]. In the same report, it is also stated that this theoretical value can yield lower results than the estimated savings potential in the practical works carried out. The main reason for this is the difficulty of using programmable thermostats [5].

According to international standards, the temperature at which the human body feels comfortable can range from 19 to 27°C [6,7]. While changing from country to country, it is recommended that this value range for houses is 20–22°C for winter and 24–26°C for summer. By setting the thermostats to the appropriate temperature, the combi boiler will run until the house temperature reaches the set temperature, and if the temperature of the house is above the set temperature, then the combi boiler will not initiate. While this is the operating logic of a standard thermostat, more savings can be achieved by reducing the set temperature by 2 to 4 degrees for cases when the household sleeps or is outdoors. The US Department of Energy states that programmable thermostats can provide additional savings of between 5% and 15% in scenarios where the thermostats can properly be set for when the users are outdoors and asleep [8]. When the savings reports of smart room thermostat manufacturers in the world are examined, it is stated that Nest saves 20%, Ecobee saves 23%, Tado saves 31% and Netatmo saves 37% [9,10,11,12].

It could be said that there is a significant saving potential even with the use of a conventional thermostat, since it is assumed that the thermostat use rate in houses with combi boilers in Turkey is below 10%, as opposed to many countries where thermostat use is required. In addition, it could be said that there is a potential of savings up to 30% in total with a smart room thermostat, which also provides extra savings for outdoors and sleeping conditions, where temperature is reduced to a lower degree not noticeable while asleep, and to a level low enough to be easily reheated when back to home. On the other hand, due to the low rate of thermostat use in Turkey, users may be hesitant to put wires through their homes or hang thermostats on their walls and thus, products that are cost-effective, wireless, easy to install and user friendly are needed to make thermostat use more widespread.

Cosa Smart Room Thermostat has been developed with the consideration of Turkey’s conditions in order to solve all these problems and to maximize savings by providing efficient thermostat use. In a section that is frequently used in the house, it is possible to control the combi boiler from a mobile phone with its easy interface by placing it at a location where the temperature can be correctly measured without the necessity of wall mounting and cable wirings. Instead of constantly adjusting the temperature, Cosa users can control the temperature in their home by choosing between home, sleep and outdoor modes. user can switch between home, sleep and outdoor modes manually, on weekly schedules or in a location-based way.

Taking into consideration the survey studies and the data of Cosa users, the amount of savings achieved by combi boiler and natural gas use, thermostat awareness and temperature preferences of Cosa users in Turkey were estimated, and the findings are provided in detail in this report.

Combi Boiler and Thermostat Usage in Turkey

Our external dependency, which is about three-quarters of energy supply, and the consequent increase in efficiency while reducing risks and prevention of waste is of great importance. Natural gas consumption in the building sector in our country is generally used for heating purposes. Examining the housing sector, which accounts for 22.9% of natural gas consumption, a survey by ERA in 2011 found that 72% of the approximately 10 million households using combi boilers for individual heating purposes created unnecessary energy consumption due to improper combi boiler use [13]. It is clear that one of the main solutions to avoid this misuse is to use room thermostats, and unlike the USA and most European countries, room thermostat use rates in our country are very low. In fact, while thermostat or control system use rate is over 95% in Europe and America, despite the fact that there is no clear data in our country, when considering the number of sales for combi boilers, it can be stated that this ratio is less than 10%. Due to the fact that thermostat use is not mandatory in many legislations on increasing energy efficiency in housing in Turkey, this rate is very low as opposed to many other countries where thermostat use is mandatory. The rates of control system use in houses with individual heating systems in the United States where the use of any control system is mandatory are given in Figure 1. According to this, 96% of the houses have at least one kind of control system and only 4% of them do not have any.

According to Nuvia’s research results in 2016, 45.4% of the combi boilers were in kitchens, 41.3% were in balconies and the rest were in different places such as bathrooms, basements and outdoors [14] (Figure 3).

When combi boiler use habits are examined, reducing the combi boiler temperatures while asleep or outdoors, so that the house can be kept at a slightly lower temperature during sleeping and the use of lower temperatures to prevent unnecessary consumption when outdoors, account for only 17.5% of the total use habits (Figure 4). In all these situations where a thermostat is not used, unnecessary natural gas consumption occurs at times when the room temperature is above the comfort requirements.

Cosa Usage Statistics

When Cosa user data were examined, it was determined that 93.6% of the users were in Istanbul, Kocaeli, Sakarya, İzmir, Ankara and Bursa. According to this, 39.8% of Cosa users are in Istanbul, 19.3% are in Kocaeli, 12.6% in Sakarya, 8.8% in İzmir, 8.5% in Ankara and 4.7% in Bursa (Figure 5).

When set temperature preferences for home, sleep and outdoor modes of Cosa users across Turkey are examined with the data in question, it is seen that 22.5°C, 20.6°C and 18.3°C set temperatures are respectively preferred in Turkey (Figure 6). According to the preferences in Figure 5, when the average temperatures in the houses using Cosa are examined, it is determined that the average temperature across Turkey is 21.8°C.

In addition to the savings determined by Cosa data and discussed in detail in the next section, Cosa users were also asked within the scope of the study about the changes in their bills and it was determined that 81.3% of Cosa users had saved on their bills (Figure 7).

According to the research results, another important finding is that 76% of those who know what a room thermostat is and have awareness on the subject do not use a room thermostat. This clearly demonstrates the potential for widespread use of room thermostats in our country.

Energy Savings

For any energy system, it is necessary for the system’s before and after conditions to be comparable under the same conditions to make it possible for these conditions to be compared after any modification or improvement. It is quite difficult to accurately calculate the reflection of any improvement in energy savings, especially in thermal systems, in uncontrolled environments, for example in housing. In general, a savings rate is calculated compared to the change in current consumption based on the energy consumption prior to the year in which the improvement is made. However, since the outside weather temperature is variable and the changes differ per year, the savings rate obtained may not be calculated correctly. In addition, changes in the internal dynamics of the system, such as the preferences and habits of users, change in population, growing-up of children in families with children, and coincidence of holidays at different times are also among the parameters affecting energy consumption [9].

Another parameter that affects energy consumption for heating in houses is structural changes in the house, such as replacing the windows, changes in insulation or heating installations. In summary, even in an environment where there are no changes in usage habits or structural changes, weather conditions changing from year to year will affect energy consumption and cause the savings amount to be calculated incorrectly. On the other hand, obtaining the current consumption data of the users and that of the previous year makes it a challenge to carry out such analyzes in our country, where it is difficult to access such data.

Taking into consideration all these challenges in calculating savings according to the consumption analysis, making this calculation based on a reference scenario instead of comparing the consumption of the previous and the following years can be considered as an alternative method. The savings rate calculations in this study were made according to the reference scenario specified for the case where the same conditions were created for all users, instead of comparing the consumption values before and after using Cosa.


In this study, combi boiler use habits of a majority of users were determined with the findings obtained from the research results and the analysis of the big data obtained via Cosa use. According to this, combi boiler use habit was constructed as the reference scenario in which the users continuously operated combi boilers at constant and low temperature before using Cosa and they continuously intervened in combi boiler temperature with regard to changing weather conditions. Therefore, the savings rates are calculated based on the amount of consumption they would make according to the reference scenario specified when the users did not use Cosa.

When thermostats are not used, combi boilers technically work by controlling the temperature difference in inlet-outlet water of the combi boiler core. They continue to run if the difference is above a certain level, regardless of the room temperature. With the use of thermostats, the operation of combi boilers concerns whether the room temperature is below or above the desired temperature. Therefore, considering that the outside weather temperature is variable in a combi boiler controlled by a conventional on/off (open/closed) system, it is necessary to keep the temperature of the core water at the optimum level determined by each manufacturer in order to be able to respond to any kind of heat demand, to heat the house in various weather conditions and to minimize the consumed natural gas to produce unit heat with more efficient combustion. This temperature is roughly 60–65°C, although dependent on the combi boiler. Therefore, in the case of using any thermostat, it is important to bring the temperature of the core water to the economic working range, if there is no control according to the outside weather temperature. In houses using Cosa, users are directed to bring the core water temperature to these levels during Cosa’s installation.

On the other hand, according to the research, a great majority of those who do not use thermostats manually adjust the temperature of the core water on the combi boiler, and in general the users keep the core water temperature at a stable temperature of 40–50°C. The amount of natural gas consumed by the combi boilers at these temperatures is different than it is consumed when the temperature of the core water is about 60°C. Therefore, although the combi boiler does not run continuously in the houses where Cosa is used, since the combi boiler water temperature is higher than before while the combi boiler is running, the amount of natural gas consumed per unit time is relatively higher, and this makes it necessary to make a more proper comparison and calculation by considering these cases separately in the savings calculations.

In this context, the saving rate for each house with Cosa is calculated on a monthly basis by using the method developed by considering combi boiler use periods and outside weather temperatures. According to this, a reference scenario is created by calculating combi boiler running periods on a monthly basis in a situation where the combi boiler runs continuously at constant temperature without Cosa use for average monthly weather temperature, and saving rates are calculated by normalizing the combi boiler operation periods obtained by Cosa use according to the reference scenario. For cases when the temperature of the core water is about 60°C for a certain period of time where the average temperature of the outside air is determined, working time of the combi boiler with Cosa use is obtained from the Cosa database. By normalizing the data obtained from the database and the actual combi boiler operation time according to the situation where Cosa is not used for the same outside weather temperature and when the temperature of the core water is 40°C, it is ensured to be compared with the reference scenario. Therefore, since the amount of natural gas consumed per unit time is higher despite the combi boiler operation time with Cosa use is shorter, this duration has been calculated for 40°C with the developed method and made comparable to those with and without using Cosa.

The steps for the method can be summarized as follows:

  • Calculating the average outside temperature for the calculated time period
  • Determining combi boiler’s operating time for the average outside temperature in the case where Cosa is not used and the combi boiler is kept at a constant temperature (reference scenario)
  • Obtaining the combi boiler operating time from the database in the case where Cosa is used and the core water temperature is 60°C
  • Normalizing the operating time for the case where the core water temperature is 40°C
  • Calculating saving rates by comparing both cases

In summary, the saving ratios obtained according to this approach were calculated according to the reference scenario specified with the assumption where the users run combi boilers continuously at a constant temperature before using Cosa and increase core water temperatures in very cold weather. For the data set, the months November, December, January and February which cover the 2015–2016 winter season, when the combi boilers are running intensively for which a statistically significant data set can be obtained. The average outside weather temperatures for the relevant months were obtained from the General Directorate of Meteorology [15].


When Cosa user statistics are examined, it is determined that 93.6% of the users are in Istanbul, Kocaeli, Sakarya, İzmir, Ankara and Bursa, and in every other city, there is at least one Cosa user. In order to obtain a statistically significant sample set, it is aimed to calculate the city-based savings rates in the cities where Cosa users are concentrated.

According to this, the savings rate calculations for the six cities where Cosa users are concentrated were carried out for the relevant four months according to the reference scenario specified in the method. Accordingly, the average saving rates are calculated as 22% for Istanbul, 34% for Kocaeli, 22% for Sakarya, 14% for İzmir, 43% for Ankara and 36% for Bursa. With the help of these data, the overall savings rate for these four months across Turkey was calculated as 31%.

Evaluation and Conclusion

In our country with approximately ten million combi boilers and which is foreign-dependent for natural gas, the use of thermostats is not mandatory unlike many developed countries. Although there is no clear statistical information, when both the research results and the thermostat sales figures were examined, it was estimated that the thermostat use rate is below 10% in comparison with developed countries. For this reason, it can be stated that a significant amount of natural gas can be saved even by using a conventional thermostat. As could be understood from the literature, it is possible to further increase the saving rates by programming the thermostats according to our daily routines. However, the usability of available programmable thermostats and the variability of our daily routines constitute a major obstacle to the realization of this saving potential.

On the other hand, in our days where technology is rapidly developing and the number of internet-enabled devices is rapidly increasing, the thermostats have started to become internet-enabled and remotely controllable by mobile applications; and thus, a new category called “smart thermostat” has emerged. For all over the world, smart thermostats are often designed to replace the existing thermostats, allowing old thermostats to be disposed and replaced with new generation thermostats. However, due to the low rates of thermostat use in our country, there is a need for a new generation of smart room thermostats that are easy to use with a simple interface and able to maximize savings with intelligent algorithms that can easily be set up without the need for cabling and wall mounting, rather than replacing old thermostats in our country. This report has been prepared within the scope of the data obtained through the extensive use of Cosa developed within this need.

Within the scope of this report, saving calculations were performed according to the specified reference scenario. Accordingly, the saving rate is calculated as 31% on average across Turkey. When considering that natural gas consumption in houses using combi boilers in Turkey is estimated to be 1129 m3 according to the data of year 2015 [2], an annual average of 350 m3 per house with a saving rate of 31%, and a monetary value of around 440 TL has been achieved.

When the aforementioned amount of savings is considered from the environmental point of view, with an annual average of 350 m3 natural gas saving per house, 630 kg CO2 emission per year is prevented. Assuming that a tree absorbs an average of 20 kg CO2 per year [16], an equivalent effect of 32 trees per house was achieved with the savings made.

When this matter is addressed in terms of the amount of potential savings across Turkey and the environmental impacts, it can be stated that with the savings rate in question, there is the potential for a total saving of more than 4 billion TL annually from the bills paid by the users in Turkey and in return, possibility to prevent about 6.3 million tons of CO2 emission. At the same time, this amount of savings is equivalent to the energy generated by all the power plants producing electricity with lignite in our country or about one third of the electricity generated by natural gas power plants.

Considering that the rate of thermostat use in our country is very low, making thermostat use mandatory in the buildings for the sake of efficient energy use through necessary legal regulations would be a very important step to actualize the savings potential presented in this report.


[1] EMO, 2015. Türkiye’nin Enerji Görünümü Raporu.

[2] EPDK, 2015. Doğalgaz Piyasası Sektör Raporu.

[3] Erkin E., Akıllı Termostatlar ile Enerji Tasarrufu ve Talep Tarafı Yönetimi, Ulusal Enerji Verimliliği Forumu, Ocak 2016, Ankara.

[4] U.S. Environmental Protection Agency (EPA), “Summary of Research Findings From the
Programmable Thermostat Market”, 2003.

[5] Peffer, T., M. Pritoni, A. Meier, C. Aragon, D. Perry, “How people use thermostats in homes: A review”, Building and Environment 46 (2011) 2529–2541.

[6] Hartley, A., 2006. Fuel Poverty, West Midlands Public Health Observatory. Birmingham, UK.

[7] ANSI/ASHRAE Standard 55–2013, Thermal Environmental Conditions for Human Occupancy.

[8] U.S. DOE, 2015.

[9] Nest Labs, 2015.

[10] Ecobee, 2015.

[11] Tado, 2015.

[12] Netatmo, 2016.

[13] ERA, 2011. Kombi Kullanım Alışkanlıkları Araştırması.

[14] Nuvia, 2016. Kombi-Termostat Kullanımı Tüketici Araştırması.

[15] Meteoroloji Genel Müdürlüğü, 2016. İl Bazında Sıcaklık Verileri.

[16] Arbor Environmental Alliance, Carco Free Facts, November 2016.