What you could do is make the filter so that they can be install inside the vents already installed in each home with central air system. As air is distributed to each room the air would pass through a charcoal type filter. You could even make the filters scented so as the air passed through them you could have the benefit of "fresh" or "scented" air. I would like mine Pine scented for that fresh smell in the bath room.

HVAC systems typically have filters, from simple to fairly elaborate, albeith they are centally installed. A per room filtered air circulator for houses without an HVAC would be good though, if they can be made quiet enough.

If you want to purchase a more effective air filter for your HVAC system you can (Lowes or Home Depot), but it will cost you both at the store (up to about $20 every 2 weeks) and in utilities (at least 10% more per month).<p>If you don't change your air filter every month it could cost you anywhere from $5 to $100 or more per month for heating and cooling. The cheapest air filters are about $0.50 each and use the least utilities (my personal choice).</p><p>Just a light coating of dust reduces air flow so your system has to work harder to provide the same level of comfort. The same effect can happen with HEAPA (High Efficiency Air Particulate) filters that trap pollens and tiny dust particles, they reduce the air flow.</p><p>Also, if the dust accumulates enough on any air filter it will often collapse. This will allow dust and debris to build up directly on your cooling coils in your HVAC system. This will cost hundreds of dollars for a proffesional to clean.</p><p>If you are considering filtering the air in a space, the small portable fans with HEAPA filters are generally more cost effective, and place the inlet near the supply vent of your central HVAC system, but don't block the vent.</p><p>More expensive HEAPA Systems for your HVAC system may provide greater overall savings over time since they are often electrical in nature and do not require filter changes beyond the 50 cent pre-filter.</p>

Most people don't have allergies and the $2500 additional cost of a HEAPA filter system doesn't apply to everyone. Many people prefer to sleep with their windows open at night.