is it possible that your HP is going into defrost mode when you do that? go outside and see if the HP is running, in defrost the outside fan does not run but hte compressor does. to defrost, a HP actually switches back to AC mode and turns on the inside strips so that it is still blowing heat. this means a little cooler air.

also, if needed my HP will run both the strips and the HP unless i switch it to emergency, then it runs only the strips. it has not been cold enough yet that my HP has cut off and run only on the strips.

I would guess that the 107 degree air is a combination of the heat pump running, doing all it can and the auxilliary strips . . . . no?

If you subtract the 85 degrees that the heat stips give you, you can see why the heat pump can't go it alone

Don

David is correct (Kasie is always correct - right David?).

The heat pump is in defrost (a/c is on) plus the heat strips. Next time you mesure this temp, take a quick run outside. The heat punmp should be buzzing and the condenser fan off.

The heat strips will give you about 13 degrees for every 5 kw (based on a blower fan volume of 1200 cfm).

So, if the heat pump is putting out 85 degree air when its frigid out and you have 10kw of strips, you should measure about 111 degrees after the air handler.

If the heat pump is not running, but the 10kw strips are (emergency heat), you should have about 96 degrees (70 supply air temp plus 26 from strips).

I just checked my system, *without* the auxiliary running. 39°F outdoors (which I know isn't to be considered frigid, LOL), 69°F to 70°F indoors, the output measured at 90°F.