Right, dual fuel system. Backup is a natural gas furnace.
Originally posted by wyounger
Keep an eye on it when you're close to your balance point in humid or rainy conditions to make sure that it's not getting so frosty that it restricts the airflow. You might also monitor your discharge air temperature to make sure it stays in the normal range when the frost does start to build up. I have a cheap digital "indoor-outdoor" thermometer with a wired probe; I put the probe in one of the registers to measure the temperature and have just left it there since. Then whenever I want to know the discharge temp I can just look at the display.
It seems like this particular unit can handle a lot of frost, though, because it has a huge single-row coil instead of something more moderately sized in two rows.
This is a dual fuel system we're talking about, isn't it?