February 2013 By Rick Odell, NATE Certified TechnicianThere has always been a need to routinely change your furnace air filter, but with new furnaces now it's an absolute necessity.Older furnaces (pre 1995) could tolerate running hotter with lower air flow. The heavier heat exchangers could handle the extra heat when air flow was restriced due to plugged air filters. However, as efficiency demands increased, heat exchangers became thinner and are at greater risk of cracking due to overheating. In addition, new furnaces monitor the heat exchanger tempurature through a control that will shut the furnace down before it gets too hot. That's a nice feature to save the furnace, but very inconvenient when it leaves you without heat.If you have a heat pump, the need to change the filter even increases. As a filter becomes plugged, the heat pump will run at higher and higher pressure, using more energy before ultimately shutting down. Once the heat pump locks out the auxiliary, or back up heat, will automatically switch on. Typically, backup heat is much more costly to run. Adding to the cost, a techinician is usually needed to reset and repair a locked out heat pump.So, change your filter every two to three months and you'll keep yourself more comfortable in your house and in your wallet. Set a reminder on your computer calendar.