What should I know before buying a air filter?

One of those stand-alone types, that say HEPA and what not. I have terrible allergies and was told to buy one, what should I buy? What should I look for? What does HEPA mean?

HEPA stands for High Efficiency Particulate Arrestance. They catch the really small stuff which includes mold spores, a common problem for allergy sufferers. For something to be called HEPA it must pass a minimum standard.

I can’t tell you which one would work best but I’m guessing that most filters are more or less alike. The big difference would be in the different air conditioning systems that would move the air through the filters.

Haj

No, no, not air conditioner, this would be a standalone type.

One of those little stand alone filters that kind of look like a stereo speaker is next to worthless. You just can’t move enough air through them to make a difference. You would need to put filters into your air conditioning/heating system to really help.

Haj

Having worked in a Precisionaire Air Filter factory, I can tell you a bit about the filters:
HEPA Filters are much harder to find and have much more material and surface area than a standard A/C or Heater Filter. They have a tendency to be pleated. You should look for thickness, and durability. In particular, you want to examine around the edges of the filter where it attaches to the paperboard/cardboard backing - if it looks like its not attached all the way around, the glue probably didn’t seal right when manufacturing and the filter will likely pull away after some use. You definitely want DISPOSABLE, NOT washable filters for severe allergies.
Make sure the device you are using to push around the air has the power to move enough air through a hepa filter- the resistance can be pretty high versus a standard A/C Heater filter. If you’re buying a stand-alone unit designed for HEPA filtration you are probably OK, but If you think you can just throw one in your existing heater or air conditioner, you may not be able to without more powerful fans in the system.

Before spending a lot of money you might want to see if you can find any solid evidence (advertising copy is not evidence) that running a HEPA filter unit in the bedroom helps reduce allergy symptoms. The last time I looked through the medical literature there were quite a few well done studies documenting no effect and a few suggesting that there might be a small benefit for some people. Caveat emptor.

Also if you are thinking of a whole house filter but the fan you have is not strong enough consider an electrostatic filter. The holes to let air through are bigger and easier on your fan. The electrostatic filter will attract particales to the filter instead of blocking them.