A house with a two-euro monthly heating bill

Thermal image of a Passive House

That won’t work at all. Make sure that you have a chimney built,” concerned neighbors advised the Radons – in the presence of their architect, Rainer Wildmann. He wasn’t surprised about their reservations, “I’ve been building energy-efficient houses for more than 20 years and I’m used to these kinds of comments.” The Radons didn’t allow themselves to be swayed by this well-intentioned advice.

They wanted to build an energy-saving passive house – with airtight insulation, a high-tech heating system without a chimney and a bright and elegant design. The building is not only meant to save energy, but also to be cosy. The family of four have been living in their dream house since November 2005. It stands in Rössing, Lower Saxony, in a group of smart detached houses. Externally, there is almost nothing to distinguish their passive house from the other buildings – except for the photovoltaic installation on the roof.

It is April and warm sunlight is shining onto the dining table through the ceiling-high window. Kea, the 10-year-old daughter, is pushing a piece of pancake into her mouth while her mother is trying to subdue her lively 2-year-old sister Ylva. It is pleasantly cool on the ground floor and the smells of cooking have long since been extracted. You only notice the missing heating panels at second glance. The ample ground floor offers a lot of space for cooking, playing, dining and living.

The Radons spend roughly two euros a month on hot water and heating. In a year, the house of Beat Duddeck-Radons and his wife Frauke consumes no more than 15 kilowatt hours of heating energy per square meter. That corresponds to roughly 1.5 litres of heating oil a year – or 345 litres of oil for the 230 square meters of living space. “That is a very strict requirement of the structural physics and can only be achieved by a combination of high-tech components and skilled craftsmanship,” says Wildmann.

Environmentally friendly materials and state-of-the-art technology

In contrast to a conventional building, a passive house is enclosed in an airtight envelope. No heat can pass through it to the outside. The Radons family decided in favour of environmentally friendly cellulose as insulation material. Accordingly, 24 centimeters of insulation material protect the house against heat loss. High-tech windows with three panes of glass filled with inert gas guarantee optimum sunshine throughput and insulation. “The windows are one of the most important components in energy-saving building, and manufacturers from Germany are world leaders in this field,” explains architect Wildmann.

The passive house uses heat from sunlight and the heat radiated by the occupants and household equipment to keep the inside temperature at a constant level of 17 to 18 degrees Celsius. However, that wasn’t warm enough for the family. “We wanted to have things cosy and thus decided to have additional heating,” says Frauke Radons. A heat pump with hot water system provides supplementary heating in the winter with geothermal energy.

Additionally, it supplies hot water for showers and washing the whole year round. To ensure a warm feeling even during frosty winters, the architect has simply taken the principle of under-floor heating and applied it to the vertical surfaces. The supporting walls contain pipes that transport heated air through the entire wall system. “It even got too hot for us during the cold winter of 2005 so we had to readjust the heat input,” recalls Beat Duddeck-Radons. This year the heating period already ended in March.

Getting fresh air in the house

Thermal energy is distributed through the whole house by what is known as a controlled ventilation system. Approximately 80% of the heat is recovered from the exhaust air and then added to incoming fresh air. Every living space has a supply air valve; the bathroom and kitchen also have exhaust air valves. “We can smell the fresh air in spring, but also the barbecue smells from our neighbors’ gardens,” says Beat Duddeck-Radons with a grin. “Otherwise, we don’t notice the flows of air inside the house at all.” There are no cold walls or floors, but a constant supply of fresh air and a healthy indoor climate.

An investment that pays off

The Radons even gave some thought to electrical energy. They have installed a photovoltaic unit on the south-facing side of the roof. Beat Duddeck-Radons does some calculations, “We receive 400 euros for the electricity we feed into the grid from the photovoltaic panels and consume roughly the same amount of electricity ourselves.” The additional costs for insulation and energy technology also pay off. The passive house was roughly 13% more expensive than a standard house. That is an investment that pays for itself through lower energy costs in a period of seven to twelve years depending on range of equipment installed.

Anyway, the Radons family feel very comfortable in their new surroundings. “In the end, it wasn’t really that expensive at all – all the technology, the large spaces and the design of the facade,” says Frauke Radons, pointing to the bright vermilion front with wooden elements. But there was one thing on which the family didn’t want to compromise under any circumstances: a comfortable home. That’s why it’s also very cosy in their house in winter – even without a chimney.