Energy consumption and cost of a shower in a block of flats

The energy consumption of a shower is roughly 16 kWh per hour, but there are variables too. Besides energy consumption, the cost of a shower depends on the price of energy. A 10-minute shower costs approx. 27 cents if energy costs 10 cents per kilowatt hour. The cost of a shower in a district-heated building varies with the season, as district heating energy charges are often considerably cheaper in summer than in winter. So in a block of flats heated by district heating, taking a shower costs considerably less in midsummer than in the coldest winter months. District heating prices also vary considerably by region, depending on the local district heating company. The energy costs of showers, and of hot water in general, can also be influenced by energy efficiency investments. In many old housing companies (taloyhtiö), considerable savings can be achieved by switching the heating system from district heating to, for example, a ground source heat pump system, or by adding, for example, an exhaust air heat pump alongside district heating. The financial profitability of these and other possible energy saving solutions in a housing company can be examined with an energy efficiency study and energy consulting by our company. Below we have collected estimates of the cost of taking a shower, based on certain assumptions. The costs of individual showers are small, but when the building’s heating costs are also taken into account and the period examined is a year for the whole building, the annual energy saving potential can be as much as tens of thousands of euros with the right energy saving solutions in a large property.

Cost of a shower in a district-heated block of flats
Shower length (min)	Cost, €
	Summer	Winter
5	0.06	0.21
10	0.11	0.42
15	0.17	0.63
20	0.22	0.84
25	0.28	1.05
30	0.34	1.26
40	0.45	1.68
50	0.56	2.10
60	0.67	2.52

*Summer: Energy price 0.04 €/kWh and water temperature 35°C
*Winter: Energy price 0.12 €/kWh and water temperature 35°C

Cost of one shower in a district-heated building (estimate)

Theory and facts about the energy consumption of a shower

The power of a shower (kW) is mass flow (kg/s) x specific heat capacity (kJ/kgK) x temperature change (K). Energy consumption (kWh) is obtained by multiplying the result of the previous calculation by time (h).

Finnish laws and decrees set the flow rate of a shower at 0.2 l/s, i.e. approx. 0.2 kg/s. The specific heat capacity of water, in turn, is approx. 4.2 kJ/kgK. This means that 4.2 kilojoules of energy are needed to heat one kilogram of water by one degree Celsius/kelvin.

Clean domestic water always enters buildings cold, and it is then heated in the heat distribution room, for example with district heating or electricity. The temperature of the domestic water entering the building varies somewhat with the season. In winter, the cold water entering the building may be slightly colder than in summer, in which case slightly more energy is also needed to heat it. If, for example, the domestic water entering the building is 10 °C and you want 35 °C water from the shower, the required temperature change is (35-10) 25 degrees. If the water entering the building is 15 °C and you still want 35 °C water from the shower, the required temperature change is only (35-15) 20 °C degrees.

When calculating the energy consumption of a shower precisely, the efficiencies of production and distribution, for example, should also be taken into account.