How do I connect a 24v air purifier to hvac?
From the Owner's manual.

Hardwiring Requirements (24V and 230V Operation)
For 24V models: Connect black and white wires to a dedicated 40Va transformer.
(Not Provided.)

Notice that it says &quot;to a dedicated 40Va transformer&quot;. This means that you'll have to install a 40VA transformer to power the device, not use the transformer in the HVAC unit.