Low Energy House

Low-energy houses are houses whose annual heating requirement is 15–50 kWh/m2. They are slightly less energy-efficient than passive houses, but the initial construction costs are lower, and the investment pays off sooner. However, low-energy houses require both heating and mechanical ventilation systems. Low-energy houses also ensure pleasant thermal comfort and high air quality. In the cold days of the winter, you will not feel discomfort between surfaces with different temperatures, such as between window glazing and ambient temperature, as can happen in traditionally-built houses. The building will be provided with a modern mechanical ventilation system and energy-efficient heating and hot water supply system. A low-energy house is a compromise between energy-efficiency, comfort, and cost of construction.

What ensures the economy of a low-energy house?

Why build a low-energy house? A “regular” contemporary house has an annual heating demand of 120–150 kWh/m2; a low-energy house uses 30–50 kWh/m2 per year. If we choose the prices of natural gas as the standard, the heating of a 150 m2 house after January 1, 2012 costs 2600 m3 × 0.5497 = 1,429 euros. We know that the cost of natural gas for households has increased by 555% over the past ten years, or by an average of 21% per year, and we can assume the price increase in the next ten years will not be smaller. In that case, in ten years the cost of a cubic meter of gas will be 0.5497 × (1+0.21)10 = 3.698 euros, and a total of 48,598 euros will be spent on heating over 10 years.

Let us assume that the construction of a “regular” house today costs 925 EUR/m2, while a low-energy house is 15% more expensive at 1065 EUR/m2. The “regular” version of the aforementioned 150 m2 house will cost 138,750 euros, while building it as a low-energy house will increase the cost to 159,750 euros. The difference between the construction costs of both houses is 21,000 euros. If you build a low-energy house whose annual heating demand is only 40 kWh/m2, you will save 35,639 euros over the course of ten years. Inserting the numbers in formulas allows easily calculating that the additional cost of a low-energy house will pay off in as little as seven or eight years, after which the house will be “making money” for you. If we assume that the house is used for 15 years, the building and heating costs of a “regular” house will be 249,853 euros, while the total cost of a low-energy house will be only 189,707 euros. Thus, you will save 60,146 euros from the 8th to the 15th year of use.

Guntis Gradovskis,
Dipl.-Ing., energy auditor,
designer of passive houses