Hi,
My home is 12 years old and I am looking to save on home heating costs.

I read somewhere that an old furnace loses its efficiency and if its 10
years old, it is only 55% efficient. Is this true? My furnace is a gas
furnace and is 12 years old.

1) If so, I am thinking of replacing it with a new one. What's the best
one out there that is 95% efficient?
How much should I expect to pay for it and also for installation?

I live in Chicago.

2) Also, is it a good idea to replace my water heaters (also gas)? Is
it better to replace them (I have 2) with "tankless water heaters". Are
tankless water heaters installed in the bathrooms or can they go in the
basement?

3) I am thinking of adding a few more inches of insulation in the attic
but concerned that too much of it may lead to condensation which could
result in mold. Any ideas on this?

Thanks.