Why ventilating in winter is essential

As soon as it gets cold outside, we see the same pattern: vents close, windows stay shut and the ventilation goes down a notch. It feels logical — keep the heat in — but in practice it backfires. An average household produces 10 to 15 litres of moisture per day: showering, cooking, laundry and simply breathing.

That moisture has to go somewhere. In a sealed home it condenses on the coldest spots: window frames, outer walls and behind cupboards. The result: fogged-up windows in the morning, a musty bedroom and, over time, mould.

Humid air costs more to heat

Few people know this: heating humid air takes more energy than heating dry air. Poor ventilation raises humidity, so you pay extra to heat that same clammy air. Not ventilating "to save energy" is a misconception.

Ventilating well in winter does not mean opening windows. An open window in January really does throw heat away. The answer is controlled ventilation: supplying fresh air and extracting stale air without losing the warmth.

How an HRV system solves this

A heat recovery ventilation system (HRV, also called balanced or type D ventilation) continuously supplies fresh outdoor air and extracts stale indoor air. The clever part is the heat exchanger: the warm extract air transfers up to ~90% of its heat to the cold supply air — without the two air streams ever touching.

The result: continuous fresh air at near room temperature, humidity neatly between 40 and 60%, no fogged windows and considerably lower heating costs than with trickle vents or a window ajar.

Already have an HRV unit? Do not forget the filters. In winter the system works hard and filters clog faster. Clogged filters mean less airflow, more noise and higher energy use. Our advice: replace filters every 3 to 6 months.