I just read an advertisment for a replacement HEPA filter which said "never needs replacing"
Why would you buy a replacement filter if the filter didn't need replacing????
The truth is all HEPA filters need replacing eventually. The questions are when & why?
Let's answer the "Why" question first.
HEPA filter media is made up of fine glass fibers produced in such a way that 99.97% of all particles 0.3 microns and larger are trapped on and within the fibers as air passes through it. In addition, a very high percentage of particles as small as 0.01 micron are also trapped. What are these particles?
Along with common household dust, HEPA filters trap molds, bacteria, smoke, dust mites, pollen & airborn virus. Exactally what you want your filter to do. BUT... over a period of time the molds and bacteria will grow on the filter media and within 1-2 years will grow through to the clean side of the filter media. Thats when the air flow sends the contaminants back into the room. Increased heat and humidity will speed up this process. I have seen a HEPA filter that sat idle in a Florida vacation home all summer long that lasted only 1 year.
This brings us to the next question, "when do I change the HEPA filter"
First, you should always have a prefilter prior to the HEPA filter. The prefilter will stop the larger particles and keep the HEPA filter from clogging prematurally. You should vacuum the prefilter every 3-4 months. With the use of a prefilter, you should change the HEPA filter every 1-2 years. One of the tell tale signs is a musty smell when you turn on your air purifier.
Some air purifier manufacturers advertize a 5 year life of their filter. It is true the filter will keep filtering for 5+ years but what is released back into your house from an old filter may not be what you expect. If you look closely at their limited warantee, you will find after 2 years it's probably more cost effective to buy a new filter.