They are no longer a gadget for luxury, but truly a necessity. However, how you do pick the perfect air purifier for your home? Here are some tips to remember.

■ An air purifier has to be the right fit for the space you wish to use it in. The best way of going about it is to match the size of your room and the coverage area of each purifier—this is usually mentioned in square feet (sq. ft).

■ Air purifiers work in the room they are kept. If you keep one in the living room and expect clean air in the bedroom, that will not happen.

■ Placement is important. You should leave space on either side of the purifier and not keep furniture too close to it. Some purifiers have intake vents at the back, and shouldn’t be placed against a wall.

■ Air purifiers have HEPA (high-efficiency particulate arrestance) filters. The thick filter captures airborne particles. Many purifiers have additional filters, such as a pre-filter to capture larger dust particles, and activated carbon filters, to capture allergens that may get through the HEPA filter.

■The quality of filters defines performance. While it’s impossible to judge how efficient one is till you use it, you could try holding up the filters to understand their thickness and the materials used. If it feels flimsy, it is probably best to avoid it.

■If there is a pre-filter to collect the larger particles of dust, this will significantly improve the life of the HEPA and activated carbon filters by preventing dust from getting lodged in them. Pre-filters are easily washable, while HEPA filters cannot be washed and need to be replaced. Depending on the brand and air purifier model, replacement HEPA filters can cost from Rs3,000-9,000.

■ Filter life will also depend on how polluted the air inside your home is. On an average, HEPA filters that don’t have a pre-filter to protect them last around six months, and those that have pre-filters, around 12-15 months.