As winter approaches and Kiwis gear up to combat the cold, health experts are sounding the alarm on a silent killer lurking in many New Zealand homes.

Unflued gas heaters, commonly purchased due to their affordability and convenience, harbour poisonous gases that can cause serious lung problems and - in severe cases - death.

As such, Asthma and Respiratory Foundation NZ is calling for a complete ban on all unflued gas heaters in New Zealand.

Unlike vented gas heaters, unflued gas heaters lack proper ventilation systems leading to the build-up of poisonous gases in homes.

Dr Lucy Telfar-Barnard, a member of the Foundation’s Scientific Advisory Board and a researcher at the Department of Public Health at the University of Otago in Wellington, says there is overwhelming evidence that unflued gas heaters pose serious health risks.

"Unflued gas heaters have no redeeming qualities - they pose multiple health hazards.

"Whether you suffer from respiratory conditions or not, use of these heaters remains detrimental."

Foundation Chief Executive Letitia Harding says we always see a spike in hospitalisations in winter, and unflued gas heaters can only worsen the situation.

"It's time for New Zealand to follow the lead of other nations and ban these dangerous appliances."

The heaters have been banned in Canada, some US States and parts of Australia due to health and safety concerns.

In response to mounting pressure, many retailers have ceased selling unflued gas heaters, however, the second-hand market remains a significant issue, Letitia says.

"While it's encouraging to see some retailers taking responsible action by discontinuing sales of unflued heaters, we cannot overlook the persistent threat posed by the second-hand market."

"Addressing this is crucial to our efforts in safeguarding the well-being of our communities," she says.

"While these heaters might be cheap to buy, the cost to your respiratory health could be high."