An eco-house with a heat pump and passive solar energy - that was still something exotic in the 80s. Katharina and Anton were ahead of their time back then. They dreamed of a sustainably built house. At an eco-fair, they discovered the design for a passive solar house. At the time, the Federal Ministry for the Environment and Nature Conservation had plans drawn up for sustainably built houses. Anton is an interior designer and planned the interior fittings himself. It was important to him that it should be a wooden house. He used larch and spruce wood for the walls and ceilings. He and Katherina like wood because of the pleasant indoor climate, but also for ecological reasons. Wood is a renewable raw material that they sourced from the North Palatinate mountains. This allowed them to save on transportation costs and also protect the climate. A total of 70 solid cubic meters of larch wood were used inside and out in their house. Anton used the leftover pieces to make built-in cupboards. When building the house, it was important to him to avoid the high levels of waste that are common in the construction industry. At the time, he hired his nephew - a carpenter - to do the woodwork. He and Katharina were under time pressure: in the 1980s, the Fraunhofer Institute was conducting a study on sustainably built houses. The institute also wanted to test the performance of the innovative heat pump in their house as soon as possible. After two years of construction, the pioneering eco-house was finished. Anton and Katharina's wooden house is a passive solar house. It works according to the onion principle. The stairwell and conservatory protect the rooms behind them from the cold. The bathrooms and bedrooms are completely surrounded by the staircase and the gallery, so that they are protected from the cold. The sun's warmth is used via the conservatory in front on the south side. In winter, the rays of the low sun reach the furthest corners of the living room. The entire north side of the house is made of wood, except for small narrow windows. This means it is optimally insulated against heat loss. At night, roller blinds prevent the heat from escaping through the windows. In summer, the high sun only reaches the greenhouse. The heat from the sun's rays still entering is reduced by the plants. The greenhouse acts as a buffer zone so that the temperatures in the house are pleasant even when it is very hot.In the 1980s, heating with a heat pump was something completely new. Anton and Katharina were unsure whether the pump would work. Based on the principle of geothermal energy, three probes were installed 35 meters deep into the ground for the heat pump. The energy obtained is compressed and fed to the underfloor heating system via a heat pump. Anton supports his heat pump with a water-burning stove that transfers heat to his underfloor heating system. This would not be necessary, as his heat pump is sufficient to heat the whole house. But on cool days, Anton likes the cozy warmth of his wood-burning stove. For him, the investment in the heat pump has paid off. It has lasted 25 years. He has now installed a new one. The pump consumes 1000 KW for its operation, but generates 4500 KW of heating energy.Their passive solar house cost around DM 750,000 in total. They paid DM 500,000, and the remaining construction costs of DM 250,000 were paid by themselves. Not a bargain, but Anton and Katharina consistently used organic building materials. These were hard to come by at the time and correspondingly expensive. Katharina and Anton built their house according to ecological criteria out of conviction and would definitely build it again. The large amount of wood in the interior, the Solnhofen lime tiles on the floor and their greenhouse create a pleasant indoor climate - and they can enjoy the warmth of the sun.0:34 Greenhouse2:00 Living room6:15 Kitchen8:03 Gallery8:30 Bedroom8:55 Bathroom10:05 Office10:43 Outdoor area11:57 Workshop