[zennmotion]

I'm not an HVAC expert, but nobody has mentioned the role or importance of the return vents that allow circulation through the system. Forced air in but no escape makes for a very inefficient system with cold rooms. People often park furniture against or near the returns thinking that's no big deal since they're not "heating" vents. Make sure that the return vents 1) exist in the cold rooms and 2) are not blocked by furniture or dust bunnies. If they're old and gross with dust restricting airflow, vent covers are often more easily replaced than cleaned