Mechanical ventilation with heat recovery (MVHR)
(cost £1,500 to £3,000)
Making our homes more efficient means more insulation and more air-tightness. As these are increased, so there becomes a necessity for providing fresh air – even trickle vents can then become the largest source of wasted energy.
MVHR is only really suitable for a building that is well wrapped up and airtight – it is essentially a form of air conditioning that extracts stale air to the outside, and intakes fresh air for the inside. On top of this, the outgoing and incoming air pass by each other through a heat exchanger, and up to 95% of the heat of the outgoing air is given up to that coming in, greatly reducing fuel bills. Having MVHR fitted will generally pay for itself within 5 years.
Generally speaking, air is extracted from areas like kitchens and bathrooms, and supplied into living spaces and bedrooms – not only does MVHR extract stale air and supply fresh, it also de-humidifies (but cannot humidify!). MVHR can also be used as a heat distributer, cutting down the amount of heat sources required.
On the downside MVHR units run continuously (unless the windows are open) and they do make a very low-level noise. Filters need to be changed twice a year, and there is a perception of risk of mould growth in the ductwork.
Installation is relatively simple, although access will be required to the ceiling voids for laying the ductwork. The MVHR unit itself is about the size of a small fridge, and is best situated with space all around for maintenance – many people install them into their lofts.