Just turned on my HVAC system

With programmable thermostats I can have the heat come on downstairs when I'm down there, and the heat come on upstairs when I head up to bed.

 

Same here ... yet the AC industry seem to suggest vents closed put a strain on AC systems ... even on the heating side;

5 Issues Caused by Closed Air Vents - The AC Hero

still - and even tho it bugs the better half, the vents in all 5 rooms of the walk out basement remained closed. It uses less energy just to maintain temps in 1,800sq feet compared to double that volume.
.

 

There's a little bit less black magic about it these days, when so many residential units use an ECM blower that can detect its own airflow (every now and then, while blowing, it cuts back the power for a moment to see how much its RPM drops, and converts that into how much air it is moving), and adjust its own speed to produce the airflow selected in the setup. If you close off some ducts, it may just speed up a little to deliver the right amount of air through the ones you left open.

You just have to make sure the static pressure in the system never goes above the specified limit, so the blower can do its job.

It's easy enough to build a rough-n-ready incline manometer out of some clear tubing and hose clips, I just mounted one permanently as part of the furnace installation, one static-pressure probe just downstream of the air filter and the other just upstream of the evaporator coil. So, if I ever want to see if the pressure's in spec, I just look.

 

... looks like mostly scare FUD from "Josh" in North Richland Hills ...

I'm not the least bit concerned about my heat pump system causing carbon monoxide poisoning.

 

It could be a legit concern especially with older blowers that weren't actively speed controlled.

I had to be careful replacing my old furnace with a higher-efficiency one, because it discharges lower-temperature air so it needs to move a higher volume. I was able to keep the old ducts, but that was after carefully checking the static pressures with the new system to see the limits weren't exceeded.