I've been reading this website for the last two months and need some advise. We are in Jacksonville, FL and own a 1937 two story 3100 sq foot house above grade. We have two 5 yeaer old systems, a packaged Payne 10 seer for downstairs and a split Payne 10 seer upstairs. During a remodeling that added an additional 600 sq. ft to the house, we had problems with rats in the flex duct. I spent two hours underneath the house but couldn't find the entry point (I traced everything back to the return that is not able to be accessed from underneath).

First, we've had some quotes to replace the units with more energy efficient but I've hestitate due to the cost vs. actual savings. I am interested in replacing the downstairs package with a new 12 seer Lennox Split Heat Pump. Does anyone have any opinions on this?

Second, the rats are gone but I hacked through one duct that seemed a little heavy and it was soaked with rat urine and appeared to have been a nest. We have had pieces of duct work that have come up through the vents as well. Would you advise to replace the flex with rigid duct? Also, what would it cost (ball park) to replace the flex with rigid or at least the cost difference between the flex and rigid for a downstairs that has 11 vents and two returns.

Thanks for any advice.