Ventilation systems' home heating roasted

17:00, May 13 2011

A new study has "well and truly busted" the idea that home ventilation systems alone can adequately warm up a house, according to Consumer Magazine.

An Otago University study has found that "positive pressure" ventilation systems did not draw down enough heat from the roof cavity to significantly alter the temperature of a typical pre-1940s wooden house in winter. It found that at best, the system averaged the heating power of five 100-watt light bulbs.

Project leader Inga Smith recommended that such ventilation systems should not be marketed as "heating/cooling" systems.

Consumer Magazine's research and testing manager, Hamish Wilson, said he was "absolutely delighted" to see the study's results.

He said the systems were effective at tackling condensation. However, "we have for a long time maintained that there won't be warm air up in the roof space on frosty nights and cold grey winter days".

He said it was misleading to claim ventilation that used roof space air could heat or cool houses, and it was also untrue that it controlled dust mites.


Ventilation systems are big business in New Zealand, and 10 per cent of homes are estimated to have one. The cost of a positive pressure system ranges from $1000 for a DIY job, to $5000 for an installed, top-of-the-line version.

But installers said the study failed to consider the wider benefits of ventilation.

Bob Batenburg, of Healthy Home Group, which markets DVS systems, said his firm was careful in its claims.

"We don't say it is a heater. There are some businesses in the market that are much more aggressive in their claims of heating up a house."

However, he said the systems could still assist heating by drying houses out and warming rooms on the cold side of a house on sunny days.

Iain Hosie, a spokesman for HRV, said the study was too narrow.

"The study focused on the heating and cooling benefit which is not the primary purpose of ventilation – which is to regularly change the air to maintain good indoor air quality."

He said better ventilation alone would not fix New Zealand's cold home problem, it also required better heating and insulation.

Dr Smith said the study was based on temperatures in a typical weatherboard house with a pitched iron roof and ceiling insulation in Dunedin, then applied to other cities through computer modelling.

It did not cover the effects of the ventilation systems on condensation, or in newer houses.

The Dominion Post