We just moved to Mid-Michigan from Northern California. Just about the
only thing we miss about our old house was the ability to grow herbs
year-round, particularly rosemary. We would like to find a way to keep
rosemary bushes alive through the winters here (zone 5b). I've read
that it is sometimes possible with the hardiest varieties in sheltered
areas.

We just replaced the original furnace in our 50 year old house and as
part of the installation, a new exhaust pipe was routed to our
foundation in the backyard. The result is a lot of warm, steamy air
comes out of the house near the ground in a particularly sunny spot.
I'm wondering how I could take advantage of this situation for the
rosemary. One idea I had was to make some sort of cold frame near the
vent to capture the heat without shocking the plants too much. Any
suggestions?