Purifiers that are Energy Star-rated by the EPA save money and power, and WiFi purifiers can be controlled from your phone. If you get just one, put it in the bedroom since you’ll probably be spending the most time in there. Full-house purifiers can be connected to the HVAC system, and as with heating, ventilation and cooling units, their filters need to be replaced regularly. HEPA filters typically last around one year, while carbon filters can go for six months before needing to be replaced and pre-filters last three months. Purifiers that use heat and ultraviolet light to clear the air don’t require filter replacement.