We ventilate our homes for many reasons, not least because we want to comply with building regulations, but mainly because we wish to maintain a healthy and comfortable indoor environment. We could adopt a seemingly simpler and cheaper approach, such as holes in the walls and simple bathroom fans to take out the warm moist air, but as we know cheap and easy options are not always best in the long run.
We are very familiar with moisture in the air outside. It is an integral part of our maritime climate in Ireland and the UK. The relative humidity is high. Indeed for a lot of the time it is in excess of 88%. For a comfortable environment it should ideally be between 40% and 60%. A heat recovery ventilation system will help achieve a reduction.
With the price of fossil fuels only going in one direction we as home-owners need to consider all options and methods of minimising our energy requirement. We do this by ensuring that our homes are not just highly insulated but are also draught free. Draughts aren’t just a matter of cold air coming in and warm air leaking out; they also have negative effects on the insulation and don’t allow it to perform to its rated maximum. Draught proofing is classed as being so important that there is now a provision in the Building Regulations (Part L) for measuring the level of draught proofing or air tightness as it is commonly referred to. See Air Tightness FAQs.
This combination of high quality insulation and air tightness measures will produce a suitably low energy solution, but only if combined with a strategy for energy-efficient ventilation.
It is important that any fresh air entering the house is inducted in a totally controlled fashion and that exhaust air has had its heat taken from it first and goes out at low temperature. In other words, the heat is recovered from the exhaust air and then used to warm the fresh air going in.
In this way, fresh air from outside, no matter how cold it gets, will always enter your house at a comfortable 18 degrees or so. This formula of Insulation + air-tightness + Heat Recovery Ventilation = comfort + health + energy efficiency, forms the basis for the ultra-low-energy strategy used in building passive houses. The video below looks at MVHR systems in passive houses.