Air Quality and Heating
As a Passivhaus requires very little additional space heating, the heating system can be
very small and simple. On very cold days, the air in the ventilation system can be heated or a small heating system with a few very small radiators can be used. Extensive heating systems with large radiators, underfloor heating or heat pumps are not necessary. In some cases gas boilers are not needed.
For most days, heat from sunlight, occupants and equipment within the building is sufficient to keep it warm.
Once fully commissioned, the ventilation system should only require regular filter changes. The number of filter changes per year depends on the air quality inside and outside, and could be required between 1 and 4 times a year. Good quality ventilation systems will include an automatic alert when the filters need changing, and will also allow warm air to be expelled during hot weather to prevent overheating.
When heat recovery ventilation systems are properly installed, the ratio of electricity required to heat loss prevented is 1:10 or better. This means that the ventilation system saves more than 10 times the energy it requires for operation.
Windows can of course be opened in a Passivhaus. It's just that in winter it's no longer necessary to worry about airing on a regular basis. When windows are opened frequently, energy consumption will be higher than for the average Passivhaus, but it will still be much lower than any conventional new building. Outside winter it is obviously reasonable and sometimes even necessary to open the windows more often, in order to get rid of any excessive heat. External shading attachments are particularly important at this time of year. When it is really hot outside, it is best to keep the windows closed and rely upon the ventilation system.