> Air purifiers can be expensive and you've probably seen articles recommending to just put a 20" x 20" x 1" furnace filter on a cheap 20" box fan and POOF! instant cleaner air for not a lot of money. It really does clean the air pretty cheap.
> There's a problem with this though. These fans weren't designed to be run with a filter. The filter will restrict air flow which will put a higher strain on the motor causing it to use more electricity and in worse cases could be a fire hazard. The higher the MERV rating (cleaning efficiency) of the filter the more stress it will put on the fan.
> Don't worry! You can still have your cheap air purifier as long as the filter area is increased to decrease the effect of air resistance. Instead of using one 20x20x1 filter we'll use two 20x25x1 filters which increases the filter surface area over 250%. It's a little more expensive because you're using two filters instead of one but the increased filter surface area also helps the filter last longer before it gets clogged up and we're saving on energy use compared to a single filter.
> There's a problem with this though. These fans weren't designed to be run with a filter. The filter will restrict air flow which will put a higher strain on the motor causing it to use more electricity and in worse cases could be a fire hazard. The higher the MERV rating (cleaning efficiency) of the filter the more stress it will put on the fan.
I'm fairly certain the opposite is true. In fact, most rowing machines work on this principle. The easiest setting is the one where the fan is as closed off as possible because it's pulling a vacuum. Less air, less resistance, easier to row / less power required to spin the fan. If anything, fans should draw less current with air flow on the inlet side restricted.
A. Putting two [larger] filters in a 'V' with cardboard to fill the top and bottom pulls the same amount of air through a larger area of filters
B. pulling the same volume of air through greater surface area results in greater pressure between the filter and fan than one filter directly affixed to the fan
C. The lower air pressure / "suction" due to an obstructed intake causes an electric fan motor to fail more quickly.
D. Increasing the air pressure that the motor is in reduces the failure rate?
But more difficult, yes? Stacking filters is very different from getting a thicker filter. The former increases air resistance, the latter decreases it. So to get the equivalent behavior from two 20x20 filters, you'd have to device some way of routing air through both of them in parallel.
I used a 25x20x4 which was easy to find. Even though I didn't do anything to stop air from flowing around the backside of the filter to the fan it still gets noticeably black fast.
> Air purifiers can be expensive and you've probably seen articles recommending to just put a 20" x 20" x 1" furnace filter on a cheap 20" box fan and POOF! instant cleaner air for not a lot of money. It really does clean the air pretty cheap.
> There's a problem with this though. These fans weren't designed to be run with a filter. The filter will restrict air flow which will put a higher strain on the motor causing it to use more electricity and in worse cases could be a fire hazard. The higher the MERV rating (cleaning efficiency) of the filter the more stress it will put on the fan.
> Don't worry! You can still have your cheap air purifier as long as the filter area is increased to decrease the effect of air resistance. Instead of using one 20x20x1 filter we'll use two 20x25x1 filters which increases the filter surface area over 250%. It's a little more expensive because you're using two filters instead of one but the increased filter surface area also helps the filter last longer before it gets clogged up and we're saving on energy use compared to a single filter.