What it’s like to live with… mechanical ventilation with heat recovery
In the second of this new series, experienced self-builder Mark Brinkley reflects on life with MVHR — otherwise known as mechanical ventilation with heat recovery
Mark Brinkley details his own experience of living with an MVHR system in his self-build
New houses are rather airtight. Or at least, they are compared to older, draughty ones. As a result, they are required to have some form of ventilation; the standard way of doing this is to fit extractor fans in the kitchen and bathrooms and to have small slots cut into the heads of the windows to let air in.these slots, known as trickle vents, are a peculiarly British way of building, and are renowned for not being particularly effective. When the wind is blowing in the right direction, they can work well, but when there is no wind, they do little beyond leaking heat.what’s more, given that all new homes are now expensively double or triple glazed, it seems bizarre to then put a hole in the window frame above.
There must be a better way. And indeed there is.you can opt for a whole-house ventilation solution that uses a large fan to blow air in and out of the home. Whole-house systems draw in fresh air from outside, while simultaneously expelling the same amount of stale internal air. They introduce control into the air quality rather than leaving it to chance, which is what happens with trickle vents. What’s more, these whole-house systems are usually designed to take the heat from the outgoing air and use it to pre-heat the fresh air being pumped into the house.
These systems are known as mechanical ventilation with heat recovery or MVHR, a somewhat ugly four-letter acronym that many people have difficulty remembering and frequently get wrong.you sometimes hear people asking for HMRV or MVRH, and the confusion creates an unearned mystique. One disclaimer: for such a system to work effectively, it needs to be installed in an airtight home — the air leakage per square metre of the building envelope should be at or below 3m3/h.m2 @ 50 Pa.
Living with our MVHR system
So what are these systems like to live with? My wife and I have had a Paul Novus 300 system in place for over a year now (in our latest self-build), designed by the Green Building Store. Just as you would hope, we are barely even aware that it’s there, let alone on. It’s so quiet that you have to strain to hear it when standing next to the main unit and it is completely silent in the other rooms.
Five ceiling registers deliver fresh air to bedrooms and living spaces while six suck out the stale air from the bathrooms and kitchen.the internal air is never stale and the house is never stuffy.you can open as many windows as you like, but you don’t have to because the air quality is always good…
Actually, that’s not entirely true. MVHR is not to be confused with heating systems or cooling systems (although there are systems which can deliver on both fronts — see page 21). In heat waves, the heat transfer mechanism