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Archive for the ‘Health’ Category

Furnace filter + box fan = cheap air filter for allergies

02 Sep

Allergy fan anteriorIf you are allergic to dust, pollen, cat dander, or other respiratory irritants, you may benefit from an air filter to remove these particles from the air you breathe. These can be expensive.

You also may be cheap and/or skeptical like me. Before buying an expensive piece of hardware, I often try out a cheaper version first, both to make sure the technology is worthwhile and to check if the cost of the fancy version is really justified. If the cheap option works, I say stick with it!

If you need an air filter temporarily (such as while visiting a house with a cat) or just like finding the cheapest solution to your problem, you may want to try the simple contraption you see here. In combination with regular doses of Claritin, this slapdash-looking filter has kept the wife happy on trips to dusty or cat-friendly places. My air-filtration system requires only three materials:

  • A common 20″ electric fan (often called a “box fan”): These are available for $20 or less at all kinds of stores.
  • A standard 20″ x 20″ pleated air filter (usually used for household HVAC systems): These can be $3 to $20 apiece depending on the size of the particles it removes. If you have severe allergies, you may want the expensive ones that remove the tiniest particles.
  • Duct tape: Any kind will do.

The construction is simple, but it is not quite as simple as just taping the filter to the fan. Follow these steps for best results:

  1. Place the filter in front of the fan and make sure they are are aligned properly. The filter will have an arrow printed on the edge pointing in the desired direction of airflow. Make sure the fan will blow air against the back of the filter in the direction of the arrow.
  2. Tape every edge of the filter to the fan. You want all of the air blown forward by the fan to go through the filter, so don’t leave any gaps. Multiple layers of tape may help.
  3. On the back of the fan, tape over all four corners of the rear grate to reduce blowback. The filter is square, while the fan’s blades trace a circular pattern. When the fan is running, some of the air pressure will leak out the back of the filter, especially at the corners farthest from the thrust of the fan blades.Covering these areas will increase the fan’s effectiveness by reducing the flow of air back out of the fan and increasing pressure against the filter.
  4. Set the fan to its highest speed to maximize the pressure against the filter. Lower speeds may not result in much airflow due to resistance from the filter. The medium and high speeds are best for providing an effective breeze through the filter.

Allergy fan posterior

If you want to clean the air in a closed bedroom to help you sleep, leave the fan running in the room with the door closed. If you want to avoid allergies in a larger space, aim the fan at yourself for a continuous stream of filtered air.

There are a few maintenance issues. Over time, the filter will become clogged with all the dust it has collected; cut or peel off the tape and install a new filter. Check the taped edges occasionally for tearing or peeling. You should also expect the fan to wear out faster because of the additional stress put on the motor from the pressures generated by blocking the air with a big filter. I suspect this would be seen by a decrease in fan speed, airflow, and electrical efficiency; I’ll have to study that part in the years to come.