That’s a very good thought. However, most newer and safer HVAC systems will shut down on low intake pressure due to flow restriction in the return air duct. If your system doesn’t shut down, operating at low inlet pressure and flow will significantly reduce performance and energy efficiency of your system.. The HVAC system in your home and office is designed to condition air temperature and humidity, Therefore, flow rate and air density across the heat exchangers within your systems is critical to operating efficiency. The higher the retention rating of a filter, the more restrictive to air flow it becomes. Reference the water/screen analogy we used above. Therefore by restricting the air flow through your HVAC system, you reduce the air density and actual total mass air flow across the heat exchangers. The net result is your AC runs longer and your electric bills get bigger. Most purpose built Air Purifiers are designed with efficiency in mind. The technically advanced RadiCal impeller and energy efficient motor used in AIRBOX™ is perhaps the most efficient integrated fan module in use today. In conjunction with the AIRBOX™ flow dynamics the total package may be the most energy efficient Air Purifier available. Over 15,000 Cubic feet per hour (CFH) of clean air using less than 60 Watts of power…you be the judge…