Indirect measures recognise that draughts can only enter the equation if the incoming air can escape elsewhere.

Here, there's a clever ventilation system that gets rid of stale air once its heat has been extracted to warm up incoming air.

His argument was that those living in the cold, less humid, north needed longer, tighter, noses to humidify and heat incoming air.

Such systems should purify incoming air but the research found that many filters were ineffective at blocking pollutants.

The design relies on the evaporative process of water to cool the incoming air while simultaneously increasing the relative humidity.