Hi @jah,
Both Ecovent and Keen Home have pressure sensors and monitor them to avoid too much pressure on your HVAC. To my knowledge, the z-wave Econet vents don’t have this feature…
(1) Here is what Keen Home says about this issue:
Can I replace all of the vents in my home with Smart Vents?
Yes you can. We recommend replacing at least 1/3 of the vents in your home with Smart Vents, but if you do replace every vent, be sure to leave at least one Smart Vent open to keep air flowing through your heating and cooling system. If you don’t replace every vent in your home with Smart Vents, we suggest leaving your standard vents open at all times.
Will closing vents harm my heating and cooling system?
Our Smart Vents have built-in pressure sensors to give you insight into the health of your system and ensure completely safe operation. As a general rule, we recommend never closing more than 50% of your total vents (smart or otherwise).
(2) And, what Ecovent says about it:
https://www.ecoventsystems.com/faq
Can’t closing vents hurt my system?
Yes, when vents are blindly closed off in a home, air pressure and temperature can rise and definitely break a furnace or an A/C. Ecovent is different. Our vents are smart and they monitor the pressure and airflow conditions in the ducts. The system will optimize your comfort, but will not put your home in a position where your furnace or A/C will get damaged. The system knows your home’s limits and will not put it in an unsafe operating condition.
In brief, the idea is not necessarily to replace all your vents, only those in rooms that are warmer or colder than other rooms, and leave the others open.
On top of it, if you look at my smartapps’ code, they will not close all the smart vents at any time during a schedule run. The smartapps will leave them open at a minimum level.
Regards.