Health experts are advising caution as people turn up the heat to combat the chill

The Asthma and Respiratory Foundation says there should be a complete ban on all gas heaters that don't have flus.

The cheap and often convenient heaters can harbour poisonous gases that cause lung damage - and even death.

Chief executive Letitia Harding says because of the health risk - they are banned in Canada, parts of Australia, and the US.

She says more than 700 thousand New Zealanders have a respiratory conditions - and unflued gas heaters can exacerbate their symptoms.