HVAC cleaning/replacement help needed
I'm moving from CT to Ohio, back into the house I grew up in. The house has been full of furniture and rugs, but empty of people for the last two years. I have kept the furnace at 50 over the winter, and turned everything off in summer, opening windows upstairs for ventilation.
The house is dusty. I'm having the rugs removed and cleaned, and I'll be dusting the floors and walls myself. I won't use the AC until the cleaning is completed.
Here are my questions:
1. Should I bother with duct cleaning? I think I want it, but don't have mold or pests that I know about, so is it a waste of money?
2. Energy audit - is it just going to tell me what I already know (windows are single pane, furnace is old) or is there something to be gained by this?
3. It's expensive to heat that house above 50, and I am planning to eventually replace HVAC. Any efficient recommendations that won't cause and arm and both legs?
4. How do I pick an HVAC contractor? I know who my parents used, and his son now runs the company.
5. Are HVAC systems like other appliances (i.e. go with name brands, but everyone has had good and bad experiences with every system) or are there brands known for reliability that are really better than others?
House and climate details:
The average high temp in OH in July is 83, and low in January is 22 (with extremes of 104 and -20). We get just under 4" precipitation per month and are near Lake Erie, so it's pretty humid all year round.
The house was built in 1964, is around 2500 sf, basement, two living floors, and attic, and has central air (electric) and a forced air gas furnace (Lennox) that are 25 -30 yrs old and still work. The humidifier died about 5 years ago and hasn't been replaced (but I need one for sure - very dry in the house in winter). I change the air filter every year and have had yearly professional maintenance - except for last year.
Thanks for your recommendations. I feel a huge responsibility taking care of this house, and I'm not sure what I'm doing.