This is precisely why i did what I did. I purchased different size “vent miser” vents from ebay. they range from 10-30/vent. there’s a little timer/controller in it that powers a small motor. I use esp8266s of varying makes (mostly nodemcu v3 but i’d probably do all wemos d1 minis if i was starting over).
I had a controller for each vent for a while but after a time started to consolidate them by running 22awg 2 conductor wire back to central spots. 3 rooms are above our garage so it was easy to pass the wire straight down into the garage and have a controller there for 3 of the bedrooms and a family type room on the other side of the garage and then another controller in the utility room handling another 5 vents.
A couple rooms still have their own controller but eventually I’ll eliminate those, too.
Temperature in each room is sensed by another esp8266 with a single 18650 lithium-ion cell strapped to it. it checks in every 4-5 minutes from deep sleep. it lasts about 5-6 weeks on a charge. i’d like to hardwire temp probes back to the central controllers eventually but i havent decided on a discrete enough way to handle that, yet.
I also take some control over the furnace with a handful of relays. The Nest runs things during the day, but at night i’m only interested in the nursery and master bed. I can use the relays to cut the 2nd stage of my furnace and lower the fan speed. if more rooms (guests staying the night?) need heat i can re-up the fan speed and gas flow. if one room heats up and closes vents before the other then i have rules that open vents to heat/cool rooms that need it most overnight.
If i want to balance temps a little but I can run the fan while closing upper vents and opening lower vents to redistribute the heat.
ive gone through a few different iterations of temp sensors. the last one is very minimal, the other is a 3d printed enclosure i made and added little solar panels on top. various pictures of the vent misers so you can see what they’re about. the black plastic part can be removed and grafted onto another vent of your choosing if you desire or you can spray paint it.
the custom designed board i designed and ordered from easyeda.com and it was way easier than i ever thought it could be and the boards come out to like 3$ a piece.
The ESP8266s all run easyesp (www.letscontrolit.com). I could have eventually programmed them to do most of what i want but easyesp makes things…easy. i can focus on the openhab rules and then set up the esps to do what i want with very minimal fuss. there’s a mini rule engine on esp easy that can make basic decisions based on what openhab sends to it. it can also answer back when commands are sent so that i can detect if there’s an error. i’m happy to share rules and more if you’d like.
there’s absolutely no reason why you couldn’t get the cost to 20-30 PER vent all in