Penny Jones, product manager at Domus Venlaon looks at the benefits oered by Mechanical Venlaon with Heat Recovery (MVHR) systems to the domesc and residenal market

M echanical

Ventilation with Heat Recovery (MVHR) systems have never been so popular. Look at

any of the property shows on TV these days and you can bet a mechanical ventilation system will be part of the house spec in one form or another. For house builders, MVHR systems have become an important means of addressing the issues borne out of making homes more air tight and are even considered a useful marketing tool; a value add. For homeowners, up to 50 per cent savings on energy bills can be achieved due to the reduced heating demand, but more importantly, there’s a considerable benefit from improved indoor air quality (IAQ). Poor IAQ not only makes for an uncomfortable home environment, but has known links to allergies, asthma, lung cancer, chronic obstructive pulmonary disease, cardiovascular disease and even dementia.

With IAQ now making it on to the national news agenda and organisations such as BEAMA (British Electrotechnical and Allied Manufacturers Association) lobbying the government to introduce policies in relation to ventilation and IAQ (see the BEAMA White Paper, Better Ventilation, Better Homes, Better Health), the uptake of MVHR systems is on an upward trajectory.

uA welldesigned and correctly installed MVHR system shouldn’t cause unnecessary noise during everyday acvies

Potentially all new homes can benefit from MVHR, including smaller properties and especially those in inner-cities where air pollution is a major problem. Some people associate MVHR systems with larger houses due to the size of the unit and the amount of ducting needed, but that isn’t the case. There are, however, certain criteria that you do need to


MVHR systems in small homes: Three key criteria for success

take into account for a successful MVHR installation in a smaller property.

Size matters

It might sound obvious, but the smaller the property, the smaller the spaces available to fit an MVHR system. Installation of the main MVHR unit in the loft used to be common practice, but with access issues and potential problems caused by lower temperatures in the loft, most units are now wall mounted within the envelope of the property; most commonly in a cupboard. The size of the MVHR unit therefore needs to be compact, especially when it comes to height; the Domus HRXE, for example, is just 507mm in height. Where installation in a cupboard is not an option, then a ceiling void should be a consideration. Here the depth of the unit and weight are key factors. The Domus HRX-aQ is the shallowest in the market place, measuring down to 199mm in depth and weighing from just 7.9kg, making it compact and light enough to be easily installed in the most restrictive of ceiling voids.

Silence is Golden

A well-designed and correctly installed MVHR system shouldn’t cause unnecessary noise during everyday activities. Look for a system that generates less than 24dBA (typically whisper quiet) at a distance of more than one meter away from the air valve.

To avoid any chance of disturbing residents, it’s still advisable to locate the MVHR unit well away from bedrooms and main living spaces. In a larger property there is greater scope for this, but with smaller dwellings this isn’t always possible. Consider the use of an anti-vibration tray, which isolates the unit from the wall to reduce any low levels of vibration induced noise which can be distracting to residents. There remains potential for sound to travel down the ducting from the fan, or from traffic noise or room-to-room- cross talk. It would therefore be sensible to include duct sound attenuators, which effectively absorb sound over a range of audible frequencies.

On the run

An MVHR system is only as good as its ducting. Poor ducting (and that relates to the product quality, the duct run design and installation) impacts the airflow, sound and overall effectiveness of an MVHR system.

uDucng for MVHR systems is normally Ø125 or 150mm (or the equivalent size in rectangular ducng)


Ducting for MVHR systems is normally Ø125 or 150mm (or the equivalent in rectangular). To maximise airflow and reduce air leakage, sharp bends need to be avoided. This has an impact on where the duct runs go. In smaller properties this can be a real issue. If this is the case, then opt instead for a Radial semi-rigid ducting system. Unlike traditional branch based ducting systems, Radial systems allow each room vent to be served by single or twin duct runs which connect directly to the central distribution system, evenly splitting the air from the MVHR unit. This can work better in small spaces. It’s also much easier to install!

improving indoor air quality by extracting stale air. In the case of Mechanical Ventilation with Heat Recovery (MVHR) systems, these go one step further by combining supply and extract ventilation in one system. They work on the principle of extracting and re- using waste heat from wet rooms. MVHR systems efficiently tempers the fresh air drawn into the building with waste stale air using a heat exchanger; up to 94 per cent of waste heat can be recovered when using a Domus MVHR system. The filtered, tempered air is then distributed around the home, effectively meeting part of the heating load in energy efficient dwellings.

M Read the latest at:

echanical ventilation systems are a cost- effective method of

Whatever the size of a new build property, there’s more than likely an MVHR system that will be suitable. You must be able to extract @13L/s from the kitchen, 8L/s from each bathroom/utility area and supply at the same rate. This is easily achievable in a modern home built for air tightness, as long as you take into account the three main points above: size, audibility and ducting. Domus Ventilation provides customers with a complete sustainable ventilation package to meet the most demanding of energy efficiency targets. It has a complete range of MVHR systems for all domestic properties, big and small.

uTo maximise airflow and reduce air leakage, sharp bends in the ducng need to be avoided

MVHR – a reminder ‘

To avoid any chance of disturbing residents, it’s sll advisable to locate the MVHR unit well away from bedrooms and main living spaces

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