Children make up 800,000 of the 1.5 million people who die each year from polluting household fuels, women account for 500,000 deaths and the remaining 200,000 are men.

"Day in day out, and for hours at a time, women and their small children breathe in amounts of smoke equivalent to consuming two packs of cigarettes per day," the WHO said.

Yet in a report entitled "Fuel For Life: Household Energy and Health," the Geneva-based agency said it could cost as little as US$6 per family to install better-insulated and fuel efficient stoves in developing countries.

"Making cleaner fuels and improved stoves available to millions of poor people in developing countries will reduce child mortality and improve women's health," WHO Director General Lee Jong-wook said.

Inhaling indoor smoke doubles a child's risk of pneumonia and makes adults three times as likely to suffer chronic pulmonary disease than those who cook with electricity, gas and other clean-burning fuels, it said.

Halving the 3 billion people worldwide cooking with solid fuels by 2015 would cost between US$13 billion to US$43 billion a year depending on the new energy source used, WHO said. Using liquefied petroleum gas would be cheaper than ethanol.

But it would save up to US$91 billion a year over 10 years due to health care savings, less illness, fewer deaths, and higher productivity due to less time-intensive fuel collection and cooking.

"With more time available, children would do better at school, while their mothers could engage in child care, agriculture or other income-generating activities," it said.