hutch,

I don't think I would judge the performance of your heat pump with temps in the 10 degree range. I assume this low temp is a rarity so I would just watch the 1st floor HP closely as the outside temps return to a more normal range. Since your 2nd floor HP is not running and able to maintain a temp of 65, then my observation is your 1st floor system is operating pretty good. There is no way to close off the second floor from the first floor? You might raise the thermostat on the second floor and see if this helps balance out the temps but I doubt this will help since heat rises. At these low temps, does your first floor HP run continuously or does it cycle and shut off occassionally? For now, I would just observe system. A 68 deg inside temp at 10 degree outside temp is darn good in my opinion.

Your current setup has the 1st floor heat pump basically heating the whole house as evidenced by a 7 degree temperature rise on 2nd floor. That 1st foor heat pump was not designed to handle the entire heat load. Unless you can close off (with a doorway) the stairway to seperate the 1st & 2nd floors, keep the upstairs heat pump thermostat setting the same as downstairs.

Thanks for the replies. While I was at work today the outside temp rose to about 31 deg. and the pump brought the inside temp up to 71. I will raise the setting on the upstairs pump. I don't have a door to isolate the floors from each other. Our December electric bill seemed abnormally high even though we had a mild month. Maybe it was due to having the upstairs turned down. Thanks again, Hutch