Specifier Review

MVHR Set to Soar

Housebuilders have been set tough efficiency goals to meet in new build properties. Ian Mitchell, Product Marketing Manager – New Build Residential at Vent-Axia, explains how ventilation is central to improving a home’s DER while improving household comfort and cutting energy bills.

With the Government keen to cut UK carbon emissions, housebuilders have been striving to improve the efficiency of homes in tricky trading conditions. As the efficiency of new homes improves it becomes more difficult to shave off extra points to improve a property’s Dwelling Emission Rate (DER). Meanwhile, as our homes are becoming increasingly air tight and thermally efficient it becomes increasingly important to ventilate effectively and efficiently to ensure good indoor air quality.

Mechanical Ventilation with Heat Recovery (MVHR) is therefore growing its share of the ventilation market with up to a quarter of new homes now featuring MVHR.  According to BEAMA, 24,000 MVHR systems were installed in the UK in 2012, and this increasing trend is expected to continue. The Zero Carbon Hub VIAQ Task Group states MVHR use will continue to grow and become the dominant form of ventilation in most new homes post-2016

Sentinel Kinetic MVHR unit
Sentinel Kinetic MVHR unit

Recent advances in energy efficient MVHR technology, in particular those with high thermal efficiency and low specific fan power, mean these systems can demonstrate a net cost saving over their lifetime. A unit ventilating a three bedroom house may consume 20 Watts which equates to an annual running cost of £22.77 at 13p kW/hr. Energy recovered may be ten or twenty times this figure.

New homeowners will also appreciate the ‘fresh air’ benefits of MVHR and the reduction in excessive moisture in the air, which combats condensation and subsequent mould growth, thus saving households money on maintenance and decoration. The improved indoor air quality also offers the duel health benefits of reducing microscopic fungal growth and eliminating the conditions in which house dust mites thrive.


Another benefit of MVHR is thermal comfort. Low energy, highly insulated modern homes are now causing a new comfort challenge as the homes are at risk of overheating in Summer. This can be a more serious problem than keeping homes warm in winter. One strategy to deal with overheating is to fit MVHR.

An MVHR system seeks to maintain the target temperature of the internal environment (it should really be known as ‘energy recovery’) therefore in summer the unit recovers ‘coolness’. This can prevent dwellings overheating by pushing the internal peak temperature later in the day. If overheat point is reached, a more sophisticated MVHR unit, such as Vent-Axia’s Sentinel Kinetic, can employ a summer-bypass to accelerate cooling by taking advantage of lower external air temperatures.

Dwelling Emission Rate

Selecting a competent person to install an MVHR system not only helps to ensure a system is performing to its optimum efficiency it also offers housebuilders a valuable SAP benefit that reduces a home’s DER.

Currently conservative ratings are applied in SAP calculations to the performance figures of centralised MEV and MVHR because specific fan power (SPF) can increase if a system is not installed correctly, affecting efficiency. The Government therefore applied ‘in use’ performance penalties to the technology’s  laboratory data results in initial SAP calculations to compensate, adding a 40% specific fan power penalty to MVHR and 30% to MEV systems.

Following changes to SAP, since January 2012 a housebuilder can choose to have ventilation installed by a competent person and at the same time reduce these penalties. Under the scheme, a trained contractor, who must be a member of a Competent Person Scheme, ensures an installation is in line with competency requirements and complies with or at least meets the performance laid out in the original system design. The installation details are then captured on a commissioning sheet which is submitted to Building Control and the SAP assessor. This information can reduce MVHR penalties from 40 to 30% and MEV from 30 to 25%, enabling housebuilders to achieve a better value for their spend in SAP.

As efficiency targets rise ventilation becomes central to improving a home’s DER. Currently we believe UK MVHR installations are growing at 20% a year, this is expected to increase as we move towards zero carbon homes targets and it becomes increasingly difficult to meet DER targets. Installing a highly efficient MVHR system can make a significant difference to a DER, saving valuable points, while providing household comfort and reducing energy bills. As a result we believe MVHR systems are set to soar in popularity.


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