How to make a DIY air cleaner that can filter wildfire smoke indoors

• New York City has the worst air quality in the world right now due to smoke from Canadian wildfires.
• The NYC Department of Health told residents to use an air purifier indoors if possible.

Smoke from intense wildfires in Canada has clouded North American cities in recent days, with New York City's air quality ranking as the worst in the world on Thursday.

In a statement posted to Twitter on Wednesday, the NYC Department of Health and Mental Hygiene said "conditions will continue to worsen this evening and we expect more of the same tomorrow."

New Yorkers were "strongly recommended" to stay inside when possible and to wear a high quality N95 mask when outdoors. Those with heart or breathing problems, children, and older adults are particularly vulnerable outdoors, it said, and anyone struggling to breathe should call 911.

People with concerns about poor indoor air quality should keep their windows closed and shut the fresh air intake on air conditioning units to prevent outdoor air from entering the home. Wearing a high quality N95 mask "will further protect you from exposure," it said, adding those with an air purifier should set it at the highest level.

How to make a DIY air cleaner using a box fan

On its website offering general guidance about indoor air quality, the US Environmental Protection Agency details how to make a temporary air cleaner if a conventional one is unavailable or unaffordable, to reduce exposure to wildfire smoke. An air cleaner is slightly different to an air purifier, which sanitizes as well as cleans air.

Exposure to fine-particle air pollution from wildfire smoke can cause health problems ranging from coughing and trouble breathing, stinging eyes and a scratchy throat, to inflammation in the lungs and a reduction of heart function with lasting effects similar to smoking cigarettes, Insider previously reported.

To create a DIY air cleaner, the EPA said to attach a furnace filter to the back of a box fan using clamps, duct tape, or bungee cords.

It said to make sure the airflow of the filter is pointed in the right direction — towards the fan.

Be sure to change the filters when they appear dirty or smell of smoke, the EPA said. When it is particularly smoky out, filters might need to be changed every few weeks or days.

These DIY air cleaners are probably most effective in a small room where you spend a significant amount of time, like a bedroom, it said.

While some air purifiers can cost hundreds — or even thousands — of dollars, a DIY cleaner can be much cheaper — filters can be bought for $25, duct tape for around $5, and a box fan for less than $20.

However, the EPA said there's limited data on how well DIY air cleaners work on smoke particles and said it doesn't recommend using them as a permanent alternative to products that are known to be effective.

How to set up a 'clean room' in your home to reduce exposure to smoke

The EPA says DIY air cleaners can be used to set up what's known as a "clean room" in the home to prevent smoke exposure during a wildfire.

Choose a room that is big enough to fit the household in, and prevent smoke entering by keeping all windows and doors closed — but don't block any exits, it said.

You should keep cool using air conditioners and fans but turn off the "fresh air" option that pulls air in from outside.

Those with a HVAC can install a high-efficiency filter to increase air filtration.

The EPA said to spend as much time as possible in the clean room to get the most benefit from it while air quality is poor.