Hi,
I’m not from Keen Home, but I’ve worked with them to develop my smartapps.
I’ve implemented many safeguards to avoid closing too many vents at once as stated here:
And, you can refer to their website about your questions:
Look under Smart Vents> Smart Vent Basics.
Will closing vents harm my heating and cooling system?
Closing off a couple vents in your home won’t harm your system, but we don’t recommend closing all of them at the same time. Rule of thumb: always leave at least one vent open at all times.
EDIT: I’ve had 16 vents for more than a year now with no issues… With my smartapps, you can configure the “closing” level which should be at least 10-20% outside of your active zone(s).
If you have few smart vents with a lot of dumb vents, of course, the “closing” level could be closer to 0…