NHBC raises the standard for MVHR systems

NHBC is setting a new standard for Mechanical Ventilation with Heat Recovery (MVHR) systems following recent research which raises issues about the performance of the technology.

Analysis by the UK’s leading standard-setting body and warranty provider has found that the move to create more energy efficient homes and improve airtightness has led to around a quarter of new homes being fitted with MVHR systems.

MVHR systems provide fresh air ventilation while at the same time recovering heat from exhaust air that would have otherwise been lost, but there is a growing body of evidence that shows that performance of these units is greatly reduced if they are not designed or installed correctly.

With most people in developed countries spending 80% of their time indoors, good indoor air quality is vital for the comfort, health and wellbeing of occupants. Poor indoor air quality can be connected with a wide range of serious health effects – including lung cancer and heart disease.

New research published by the NHBC Foundation monitored ten homes in Slough built to level 6 of the Code for Sustainable Homes over an 18 month period. The report ‘Assessment of MVHR systems and air quality in new homes’ found that nine of the units were recommissioned and one was replaced after approximately one year of occupation. Previous research by the NHBC Foundation and Zero Carbon Hub has also revealed a number of issues with MVHR systems.

In response to this research and following wide consultation with the industry, NHBC is setting a new standard for MVHR which will be included in the 2014 edition of NHBC Standards. This technical guidance, which will be issued to NHBC registered builders in October, will cover issues such as system design, ductwork, location of the fan unit and prevention of condensation.

Paul Cribbens, Standards Manager at NHBC, said:

“MVHR systems can offer significant benefits and increasing numbers of house-builders are using them as a practical and cost effective way of meeting ventilation and energy efficiency requirements.

“But these systems must be correctly designed and installed or design performance can be greatly reduced. NHBC’s ground breaking new standard for MVHR is a significant step forward which will benefit both homeowners and the industry.”