You only have 2 choices.....Lennox & the rest of them.......Most heat pumps I know of call for backup at around 28 degrees...My Lennox Hp26 will keep heating way below 28 degrees...My neighbor has gone thru a Trane 900 and 2 1200s while this Lennox keeps on ticking..

If I had to replace it and couldn't with a Lennox I would choose a York..