Pollution indoors could be three times more harmful than the outdoor environment because of our energy use, according to a new study.

Researchers at the University of Sheffield’s Faculty of Engineering measured the quality of air inside and outside three residential buildings in a city centre compared with different types of energy use like gas and electric cookers. They found the levels of nitrogen dioxide (NO2) in the kitchen using a gas cooker was three times higher than the air outside the property.

Professor Vida Sharifi, who led the research said: “We spend 90% of our time indoors and work hard to make our homes warm, secure and comfortable but we rarely think about the pollution we might be breathing in.

“Energy is just one source of indoor pollution, but it is a significant one. And as we make our homes more airtight to reduce heating costs, we are likely to be exposed to higher levels of indoor pollution, with potential impacts on our health.”

The research also found the NO2 levels in the flat kitchens with gas cookers were much higher than the levels set by the Government for outdoor air quality.