Thanks for taking the time to reply.

I only have two bedrooms that I can close off, and even then, a little
air gets through the vents.

I always open them if I am gone, to avoid any freezing problems.

And, I also open cabinets where sinks are underneath.

Many thanks.

Corinne

wrote:
To the list of considerations, I would add:

Keep in mind you have these closed off registers if you set back the
temp for an extended period when you are away. A room with some water
pipes may be fine if the rest of the house is at 70 but freeze if you
turn the heat down to 45 while you are away on vacation. If you have
any concerns about anything freezing in that room, I'd leave the door
open when you turn the heat down for an extended period. It's also a
good idea to open the doors to cabinets under sinks with water pipes in
the exterior wall with the heat set low, for the same reason.