Twenty terrace houses without a traditional heating system has been built in Lindås, Sweden. The houses are extremely well insulated and very airtight. They are equipped with a high efficiency ventilation heat recovery system. Each house also has a 5 m2 solar collector that is designed to cover 50% of the energy supply for hot water use. The total electricity consumption and the air temperature have on an hourly base been monitored in two positions for each of the houses. Further has the environmental conditions, i.e. outdoor temperature, wind, sun etc been monitored. In six of the houses separate measurements of electricity consumption for ventilation and hot water has also been performed. In these six houses also the temperature and humidity in the bathrooms has been measured. One of the houses has been used for more extensive measurements. In this house the presence of inhabitants has been simulated by the use of electrically heated manikins. Humidity gain is achieved by remote controlled showering in the bathroom. During the summer of 2003 an automatic window airing system was also introduced. The results show that the mean value of the indoor air temperatures in most cases is equivalent to or higher than those expected in houses with a traditional heating system. The fluctuations are however sometimes a little bit larger. The total energy use is on an average much lower than for a traditional house with a heating system, but still higher than estimated when designing the houses. The heat from household electricity consumption is in most cases more than sufficient to keep the indoor climate within acceptable limits. However, some additional heat source is required for some periods during wintertime. For these houses most of the heat required can be supplied through a small reheater in the air-handling unit. In the actual case, the reheaters in the gable houses should have been larger and some additional heater in the upper bathroom would have increased the thermal comfort. The air-handling unit control system did initially not work properly. In spring, summer, autumn and sometimes even in the wintertime, window airing is necessary to keep the indoor air temperature down to a reasonable level. The automatic window airing system showed promising results. The conclusion is that it is possible to build well-insulated and very airtight houses without a traditional heating system in a Nordic climate.