Our air conditioner died this summer. It was 30+ years old. While the repair guy was out there, he replaced the air, heater, added a return, etc and told us it would significantly lower our heating and cooling bills. What timing. So glad I did it. Our bills are actually about 1/3 lower. Adding the extra return really helped a lot too and was not very expensive to do. In all it was $6,000 to do everything but I think in a few years, we will break even and then make $$$.