Tom Hull, frequent NEWS' contributing writer and vice president of service for Rosenberg Indoor Comfort, San Antonio, recently published an e-mail newsletter regarding properly installed HVAC systems.

In the e-newsletter, Hull said, "Most residential heating and air conditioning systems, when they are sized and installed, are calculated on an ‘average' outdoor summer temperature of approximately 95 degrees with an average indoor temperature of 75 degrees. So, for every degree over 95 outside, your system is operating ‘outside' its rated area, so to speak. When it's 100 degrees outside, the temperature differential (the difference between the outside and inside temperature) goes up. Guess what else goes up? We call it infiltration and induction."

To see the full text of the newsletter, e-mail Hull at mrosen3565@aol.com.