My furnace and AC are both about 15 years old, I think they are on
their last legs, so I am thinking about replacing them. AC struggles
mightilly to keep up in warm weather, leaks the water that it takes
out of the air. Furnace is just old, although no major problems.

I live in a 4 bedroom, 2 story colonial, I think 2000 square feet.
Have 7 kids so doors are never shut. Live in Michigan, cold winters,
humid summers. Don't want the kids growing up soft.. so I don't feel
the need to run AC all the time, just a few weeks a summer when it is
really hot and humid. Forced air/Natural gas.

Have a few questions:

* Is it wise to replace because it it old, or should I wait until a
breakdown? (I happen to have cash on hand now, may or may not have
cash in future when it breaks down)
* Is it likely that a new unit would be more effient and start saving
me significant money? (that is part of my thinking on replacing it
now, instead of waiting, any validity in that avenue of thought)
* I get from a few general conversations that I should avoid the super
efficient models for some reason, what is the thinking there?
* Any general recomendations on considerations when looking at AC?
* Is there any advantage in replacing both AC and Heater together?
* Any good Web sites where I can do general research before I start
looking at specific brands or systems?
* Any general ideas on cost, I realize they probably vary greatly, but
any ballparks.
* Can I save money by hauling out old furnace myself (if it will save
a couple of hundred bucks, I have a saw-z-all and a couple of
brothers, how tough could it be??) obviously I would have to safely
vent refrigerant, which is probably freon, due to age of system.

Any Advice welcome--