This place is gorgeous

I bought my first house all by myself and I was very proud of being able to afford it. I was only in my early twenties at the time and most of my friends could barely afford rent let alone a mortgage payment but I had worked very hard all the way through high school to put money in savings and it had paid off. Now, some 15 years later, I am getting ready to sell that same house and I need to make sure that everything is ready before I put it on the market. I had all the major stuff checked like, the roof, windows, foundation, things like that, but when it came to my HVAC system I ran into a problem. I never really put much thought into my heating and air conditioning unit and had failed to have annual inspections done for the past several years.  I guess my life was busy and I felt that as long as when I turned it on it worked, there wasn’t a problem. I called my local HVAC company to have them send out a technician to look it over assuming that everything would come up just fine. After a thorough inspection he came up to me with some very bad news and I knew it was going to cost me a lot of money. The system was only working at about 60% efficiency and needed some serious attention as well as the ductwork needed to be cleaned out. Even with everything that they were able to do it would only improve its in efficiency by about 15 to 20% and I would have to disclose that on my sellers agreement. Armed with this information I talked to my realtor and decided whether I should sell the house at  the lower price to compensate for the HVAC system or replace it. Either way it will cost me money.