Ventilation Systems

Click image for larger size


  • Cold air ducts should be kept outside, and warm air ducts inside the insulated building envelope, unless they are well insulated and not very long.
  • The ducts length should be minimised as much as possible, with smooth inside surfaces and airflow velocities ≤3 m/s (9.8 ft/s).
  • Include sound attenuation, and fire protection measures.


  • Place central unit and air-to-air heat exchanger near the thermal envelope (good locations are in the envelope, or on the lower floor).
  • Place the air heater inside the insulated envelope, and provide additional insulation of the central unit and air heater as appropriate.
  • Heat recovery rate should be ≥75%, system should be air tight (leakage < 3%), with electricity efficiency < 0.4 Wh/m³ (0.04 Btu/ft³), and should be adjustable, with a housing that is well insulated acoustically and thermally.

Ventilation controls:

  • Provide user-operated settings for "low", "normal" and "high", and consider additional controls in kitchen and baths / toilets.

Underground earth-to-air heat exchanger (optional):

  • The system should be airtight, with colder parts away from the house, and a bypass (for periods when heating or cooling air to earth temperature is not desired).