Expert: Howard Livingston - 5/15/2009

Question
Is there a standard for temp differences from outside to inside to determine how well insulated a house is?  Such as it's 90 degrees outside and what temp would it be inside a well insulated home without a/c running?  Just wondering because it's only been in the 80's outside and our a/c already has been running off and on since we have thermostat at 78.  Is that normal?  We do live in old house but have dual pane windows and solar screens and alot of shaded areas.

Answer
Good question. There is a rule of thumb that is surprising. Here it is.  With a good accurate thermometer measure the temp inside the return air grille for 5 min. Go to a supply air grille about 1/2 way out from the furnace & measure the temp INSIDE the grille. The differenc should be 17 degrees. If ONE degree high or more the heat load is too high. ONE deg. low or more its running too cool. Its sensative so read accurately. Then go figger what you need to do !!