Had Air Scrubber put in HVAC... fan is on 24/7... but it no longer can maintain the temperature?
I would check if you have a make up air vent, this vent is on the intake side of the furnace and may be on the intake duct in the attic or to an outside location. They are usually not allowed in garages that makes sense CO and rarely put in crawl spaces because of damp musty air.
With cold temps a open make up air duct set up for intermittent use may be cooling things two much for constant use, I put baffles or adjustable dampers on the ones I have installed for this reason.
If you can find the make up air vent reducing the size of the opening may be all you need. For 24 hour operation I will take the opening down to a small opening not much is really needed on a 24/7 system.