An open question. What is the correct temperature differential between the supply and return on a central A/C system. I have read or heard anywhere from (11 to 15 degrees) to (14 to 20 degrees). Using an infrared thermometer I seldom register above 14 degrees. I have replaced batteries and made sure I’m not more than 2 ft away from a register thinking it was the thermometer. I had one instance on a new house where I could not get more than a 9 degree differential. I ran the A/C for more than 45 minutes and could not get the room temperature below 76 degrees (according to the thermostat the temperature started at 78 degrees). I reported this as needing to be checked by an A/C contractor. I later heard through the realtor that they found no problem and I probably didn’t know how to work the thermostat. The system was 42,000 BTU for a 1800 sq ft (under air) house. Should I be using a different type of thermometer? Any comments?
Craig…1st read all 117 posts in this thread: http://www.nachi.org/forum/showthread.php?t=3809&highlight=differential . If you’re still confused come back to this one…
Craig,
there has just been a big discussion on this topic in the HVAC section
Regards
Gerry
:roll: 
:roll: