But China could arguably benefit more from them, considering its extreme air pollution.

So Chen decided to revamp his three-bedroom apartment near the Shanghai Railway Station when he moved in.

Workers followed his design to build four air outlets and intakes in the ceiling and furniture in the dining hall and three bedrooms. The main opening is in the southwestern bedroom.

The ducts are dotted with small holes and filters at their ends. Two motors over the bathroom expel air every two hours, using a timer in the shoe cabinet in the doorway.

Chen also installed PVC windows over the original windows, cutting down not only air pollution but also noise.

The materials cost 2,000 yuan. That's for 20 meters of PVC piping ranging from 10 to 15 cm in diameter, a timer, two silent motors and filter traps.

The rest went to paying laborers to install the system.

The facilities aren't visible. They're concealed in the interior design well enough that a visitor wouldn't know they were there unless told so.

Chen demonstrates the system by placing tissue on one of the intakes. It sticks.

"If someone smokes in here, the odor will disappear very quickly," Chen says.

Chen's system has inspired others to revamp their homes, including not only his friends but also a European who read media reports about it. The man contacted Chen for instructions.

"I told him how to install the system, and he hired workers to do it," Chen says.

Chen is among a growing number of grassroots designers in China who are creating innovative and DIY solutions to smog. But he stands out in that many tinkers are focusing on filtration - i.e., high-efficiency absorption filters taped to the fronts of fans - rather than ventilation.

Some environmental experts have expressed doubts Chen's system could filter out PM2.5 - particles with diameters smaller than 2.5 microns that the respiratory system can't block.

The World Health Organization recently named air pollution, and especially PM2.5, as a leading environmental cause of cancer deaths.

Chen says more tests need to be done to answer the small particle question.

But he points out his system is cost-effective.

"Only purifiers used by the semiconductor industry can completely filter PM2.5," he explains.

"But they're very expensive. Installing those in homes would be like using a cannon to blast a mosquito. We need more research on which filters effectively fight PM2.5 so we can clear these particles from our homes."