Ventilation sounds expensive. Do I need it?

Yes. Without mechanical ventilation, indoor air quality is very bad for human health. Moisture, VOCs and high CO2 are major contributors to respiratory disease. In fact, the CO2 levels from sleeping in a closed bedroom can be higher than 2000 parts per million (ppm), and this level of exposure can reduce cognitive decision-making performance by 50%! No matter how thermally efficient your home is, your home needs ventilation to be healthy. When considering ventilation systems, avoid the DVS/HRV positive pressure systems that require gaps in the building envelope where moisture and heat are forced out.  These use more energy to pre-warm the air with heating elements when the weather is too cold to heat the air in the roof space. In contrast, a balanced energy-recovery system removes stale air and replaces it with clean, fresh air at the same rate. It is also fitted with a heat exchanger that actively recovers heat energy from the outgoing stale indoor air to pre-warm incoming fresh air. As such, the need for additional heating of fresh air is reduced. There are many different models to choose from, some are just as inexpensive as a positive pressure system or a small heat pump.