必须更换，在北京如果一直开的话不可能半年更换。
滤网分初滤和hepa滤网，初滤最好每周都能清理一下，不然非常恶心。
hepa的寿命我是不知道，但是看到黑黑的滤网就不放心。

hepa有对应的级别的，但是商户说自己是E10，谁知道呢。。。
下文转自wiki
HEPA filters, as defined by the DOE standard adopted by most American industries, remove at least 99.97% of airborne particles 0.3 micrometers (µm) in diameter. The filter's minimal resistance to airflow, or pressure drop, is usually specified around 300 Pa at its nominal flow rate.

The specification usually used in the European Union is the European Norm EN 1822:2009. It defines several classes of HEPA filters by their retention at the given most penetrating particle size (MPPS):

HEPA class     retention (total)     retention (local)
E10     > 85%     ---
E11     > 95%     ---
E12     > 99.5%     ---
H13     > 99.95%     > 99.75%
H14     > 99.995%     > 99.975%
U15     > 99.9995%     > 99.9975%
U16     > 99.99995%     > 99.99975%
U17     > 99.999995%     > 99.9999%

【 在 daguaibing (绒猫~大乖饼) 的大作中提到: 】
: 好像是换，半年一换
: 还很便宜，大概几十块钱
: 所以我觉得这么便宜一定不能除pm2.5
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