Themo Smart Thermostats Optimize the Electricity Consumption of a Detached House


In August 2021, Antti Pesonen had 10 Themo Smart Thermostats installed in his detached house built in the 1990s. Within a year, they have reduced the consumption of electricity by almost 20% by optimizing underfloor and ceiling heating, when compared to actual consumption in previous years under similar outdoor temperatures. Themo Smart Thermostats also play an important role in the development and implementation of smart control at home.

Comparing the Annual Consumption of Electricity Requires Skill


The annual consumption of electricity in an electrically heated detached house can vary quite significantly depending on the year. Outdoor temperatures during the winter months are decisive in terms of consumption.

Antti has monitored the consumption of electricity in his house at an hourly level over the past 10 years. He has also downloaded hourly temperature data from the Finnish Meteorological Institute for the same period.

In 2012–2021, the consumption of electricity in Antti’s house ranged from 29 068 to 34 237 kWh. When the Themo Smart Thermostats were introduced, the annual consumption from the beginning of September 2021 to the end of August 2022 was noticeably lower than ever before at just 24 140 kWh.


Electricity consumption before (black bars) and after (purple charts) installing Themo Smart Thermostats.The vertical line indicates the influence of the outside temperature on the heating demand in an electrically heated detached house.


When the consumption of electricity is compared annually, comparison of the consumption figures alone is not enough, as the outdoor temperatures vary from year to year. The most accurate result is achieved by comparing the amount of electricity consumed previously under the same outdoor temperature. Based on calculations, the amount of electricity consumed at Antti's home within the past year at the same temperature would have been 29 722 kWh on average. This means that the comparable savings amount to 5 582 kWh or 19%.


“The best thing about Themo Smart Thermostats is the fact that in addition to a reduction in electricity consumption, it also allows you to easily monitor and control the consumption and room-specific temperatures. Themo has also provided me excellent service and a valuable sparring partner.”


Antti's calculations show that there is a very high correlation between the outdoor temperature and the amount of electricity consumed by heating. For example, an increase of one degree in the outdoor temperature reduces the electricity consumption by heating as much as lowering the indoor temperature by one degree when heating is on. This also confirms the received wisdom that lowering the indoor temperature has a significant impact on the size of electricity bills.

Taking Advantage of the Electricity Contract Type and Night Electricity


Reduced consumption of electricity is not the only source of savings provided by Themo. Themo Smart Thermostats optimize the consumption based on the lowest rates, which means that the price of the electricity used is lower than average when using exchange electricity.

Another source relates to the transmission price of electricity. Just like in the electricity contract, customers can choose between day and night rates in the transmission contract. At night (22:00–07:00), both electricity and transmission are more affordable. If the consumption of electricity is shifted toward the night-time, more savings can be achieved. When optimizing the consumption of electricity, Themos also takes the transmission price into account. According to Antti, you should also adjust your boiler to only heats up at night. 

Before the installation of the Themo Smart Thermostats, 60% of the electricity consumed at Antti's home was used during the day and 40% at night. With Themos Smart Thermostats, consumption has noticeably shifted toward the more affordable night-time hours. During the first year, consumption has been at a similar level at both night and during the day. It would be difficult to increase the use of night electricity further without washing laundry and using the sauna only after 22:00.

“I recommend Themo Smart Thermostats to anyone who is interested in saving electricity, the environment, and novel technology. While, for example, reducing the consumption of electricity by underfloor heating in the bathroom requires no special skills or dedication, Themo does also provide DIY enthusiasts like me the opportunity to create a smart home based on their needs.”


Turning a Detached House Built in the 1990s into a Smart Home


Antti identified suitable temperatures and appropriate heating times by monitoring the room-specific temperatures. The next step was to create two different schedules: At Home and Away. In the At Home mode, the daily schedule adjusts the target temperature of the Themo Smart Thermostats 4 times per day: slightly cooler at night and during the day, warmer in the mornings and evenings. The temperature in the bathroom is higher than elsewhere to ensure that the floor is properly dried. The temperature is also slightly higher in the bedrooms at night. The Away schedule is the same for each room. Now heating can be controlled with a simple decision between At Home and Away. 

The Themo Smart Thermostats utilize machine learning and are able to reduce the consumption of electricity even if heating is not actively controlled. Antti is particularly interested in novel technology, which is why he has created his own application to monitor and control the consumption of electricity throughout the house from a mobile phone or smart watch. Themo offers an excellent API interface and instructions for just such purposes. This also allows Antti to control and monitor all Themos at once. Themo is also developing its application to include similar features.

Read how Antti took ThemoSmart Thermostats into use

Is your house equipped with underfloor heating? Purchase a Themo Smart Thermostat from our online store and begin saving electricity and conserving the environment!

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