Okay, here goes. Moved from the North East US where I had an oil burner/water baseboard radiator set up (Sounded like a Jet Engine) to the South East US where we now operate dual Heat Pump/AC configuration (brand unknown but purrs like a kitten in comparison). Anyway a couple of questions. My units are about 5 years old, larger one blower unit in crawlspace handles the lower level. Smaller unit blower unit in attic handles upstairs. Both have fanned units side by side outside. 1) Its been cold here lately getting down to about 15 at night and around 35 during the day. About what temp does a unit loose effeciency and auxilary heat is needed? Both units have auxilary heat strips that can supplement heat and dramatically boost the temp at the registers. Both thermostats have dual mercury switches one for normal heat and one for "emergency heat". It seems like the lower unit runs constantly on cold nights blowing air that is only a few degrees warmer than the room air if that much. 2) Sometimes, not always we get strange odors emitting from a few of the registers. The odors seem random sometimes downstairs in the bedroom, sometimes in the kitchen, sometimes here , there, etc. Sometimes upstairs and sometimes downstairs, sometimes not at all for a few days. It smells like the previous owner stuffed dirty laundry into the ductwork. (I hope not) I changed the filters and that seemed to help for about a week is all. Gross!!! Please help if you can.