hammy
not good at conversion from C to F but if my calculation is correct, you are about -15 deg fah outside temp and your supply temp at register is about 77 deg fah which is low. Please confirm.
what area do you live?
what is your stat set at? is home's inside temp being maintained?
is your air handler running continuously or cycling at all?
do you know the size of your heat strip? I am just guessing from the number which looks like a 15 KW which is about 50 KBTUs.
I will offer an opinion. either your heat strip is defective and needs replacing or it is undersized for the weather you are experiencing.
post back.
TD
