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Mon November 30 2020

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NHBC acts on MVHR failures

24 Sep 13 Widespread problems installing mechanical ventilation with heat recovery (MVHR) systems has prompted the National House Building Council (NHBC) to re-write its technical guidance.

MVHR systems seem like a good idea but have been prone to failure
MVHR systems seem like a good idea but have been prone to failure

An estimated 25% of all new homes are now fitted with MVHR systems in a bid to make them more energy efficient.

However, a study by NHBC found has revealed widespread problems with these systems that recycle airflow within air-tight homes.

“With MVHR already being installed in around one-quarter of new homes, it is clearly essential that the concerns identified are dealt with urgently,” NHBC said.

The NHBC Foundation monitored 10 homes in Slough that were 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 had to be recommissioned and one replaced after approximately one year of occupation.

The study was prompted by previous research by the NHBC Foundation and Zero Carbon Hub that had also revealed a number of issues with MVHR systems.

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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. Poor indoor air quality can be connected with a wide range of serious health effects – including lung cancer and heart disease.

NHBC is now working on a new standard for MVHR systems. This will be included in the 2014 edition of NHBC Standards and issued to NHBC registered builders next month.

It will cover issues such as system design, ductwork, location of the fan unit and prevention of condensation.

NHBC standards manager Paul Cribbens, 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.”  

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