Something new to think about (at least new to me.) When replacing older SEER rated heat or ac units, you should replace both not one or the other. For example, I have a furnace and AC unit, both are rated 15 SEER (seasonal efficiency energy rating---google it for a more detailed explanation.) If I decided to change the AC unit to a new 15 SEER one and leave the old 10 SEER furnace installed, I wouldn't really be improving anything. Whatever is the weaker unit will be what the other unit works to. So, even though I've got this great efficient 15 SEER unit, it will only work as a 10 SEER unit (effectivley I would be loosing @ 40% in electricity that I could be saving.)
Food for thought when trying to get by with keeping that old furnace/heater/air handler for a while longer.

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