Well, Ill tell you right now your heat pump is probably "Locked out" on low temp and youre stuck with emergency or back up heat until the temps get up a little bit. Heat pumps usually lock out around 20* because they cant create enough heat ransfer below that to keep up with a homes heat loss. the call it the balance bubble and it depends on the pumps efficiency.....SO until it warms up you might be stuck with emergency heat. Its hard to explain this all to guys who don't do this kind of work, but I hope this makes some sense.