The health benefits of MVHR
In this article, as part of the 15th anniversary celebrations, our team member Ben looks firsthand at the health benefits of Mechanical Ventilation and Heat Recovery (MVHR). His experience of MVHR is as positve as Dave’s who posted on the subject 8 years ago.
Having lived in a house without an MVHR and then living in a house with MVHR, I’m really shocked about how much of a difference it has made. The first surprise came when opening the machine to change the filters. As you can see from the picture above, they were pretty horrible! The filters are specially designed to minimise impurities like dust and pollen, so just imagine how dirty the house would have been without the MVHR!
Before we examine how an MVHR unit has affected my house, let’s have a look at all of the different types of ventilation.
Background ventilation is a requirement of Building Regulations. Under part-F four basic systems for ventilation have been identified:
- Trickle Ventilation – As the most basic form of ventilation, trickle ventilation is simply a small hole set into window frames around the house, often with a cover to allow the amount of air to be reduced and prevent extreme draughts. If you are spending lots of money on fancy new triple glazed windows though, cutting lots of holes in them doesn’t seem like the best thing to do.
- Passive Stack Ventilation (PSV) – Passive Stack Ventilation, is a slightly more scientific method of ventilation as it relies on the air leakage from holes already in the house. The PSV system then uses the fact that warm air rises, to pull stale air in the house through an exhaust duct through the roof. However, to prevent your house turning into a massive vacuum and getting rid of all that precious breathable air building regulations require that Trickle Vents are still used. These ducts need to be installed vertical and never below 45deg to work.
- Mechanical Extract Ventilation (MEV) – Mechanical Extract Ventilation works in much the same way as the Passive Stack system however it uses a fan to pull air out of the house. Using a fan also means that it can focus on wet rooms such as Bathrooms and toilets. Much like the Passive Stack system it still requires the use of trickle vents throughout the house.
- Mechanical Ventilation with Heat Recovery (MVHR) – Required in all Passivhaus buildings, MVHR is in my opinion the best option on this list as it has no need for holes in all the windows. Instead, fresh air is drawn into the house through intake vents, and at the same time stale air is sucked out of wet rooms and past the fresh air on its way outside. As it passes, without mixing, the stale air transfers it’s heat onto the fresh air keeping heat loss to a minimum. The continuous movement and filtration of the air also means that toxins and harmful chemicals in the building are dramatically reduced.
It is shocking how much warmer it keeps the house, even during the coldest winter months. When it was a chilling 50C outside, the MVHR unit managed to keep the supply air at 200C, just one degree cooler than the air it was extracting! Don’t worry though the heat exchange automatically stops when the outside temperature is hotter, so it even helps to keep the house cool in the summer.
Before the machine was put in, I was nervous that it would be far too loud to allow any real concentration, but I can honestly say that even when it’s on boost mode I can hardly hear it at all. It’s quieter than the fridge. MVHR is a good investment for your new Passivhaus too, because the heat energy saved can be up 15 times required to run the machine.
