MNRebecca wrote:
The extra elbows and extenders...they're not going to make it too hard
for the furnace to get air through the intake pipe, are they?

A couple elbows shouldn't matter unless you have a lot of piping getting there.

On my house, the intake pipe comes out of the wall , with a downward facing
elbow to prevent water/dirt entry. The exhaust pipe has 2 elbows so it jogs
down, then points straight out from the wall so the exhaust is directed away
from the house and intake. A short length of pipe on the downward jog can be
used to keep it from hitting plants that might be damaged.

CO should not be an issue. If some exhaust gets drawn into the intake, it will
just go through the burner and right back out. It won't stay in the house.