Uneven Cooling Between Rooms

Rooms with shorter, larger ducts get most of the airflow. Rooms with long, narrow, or restrictive duct runs get less. Single-stage system can't compensate. Most common in homes 15+ years old without zoning.

Measure airflow at each supply vent (anemometer or hold tissue paper). Compare CFM by room. Rooms with much less airflow have restrictive ducts.

Bedrooms without return air grilles can't allow cooled air to leave when doors are closed. Room pressurizes, supply air stalls. Most homes don't have bedroom returns.

Close the door to the problem room. Does it cool less with door closed than open? Feel under door — air should flow out easily.

Multi-story or large homes need zoning — separate thermostats and dampers for different areas. Single-zone with one thermostat creates unavoidable imbalance, especially upstairs vs downstairs.

Single thermostat for entire home. Significant differences between floors (especially upstairs hotter in summer). System works fine in some rooms, poorly in others.

Some rooms have much more heat gain than others — west-facing rooms (afternoon sun), rooms with vaulted ceilings, rooms above garages, rooms with poor attic insulation. Single duct sizing can't compensate.

Touch ceilings and walls during peak heat — hot to touch indicates poor insulation or solar gain. Compare problem rooms to comfortable rooms.

Specific duct runs have major leaks or disconnections, losing 30-70% of conditioned air to the attic/crawlspace/wall cavities. Only rooms served by those leaky ducts are affected.

Inspect accessible ductwork. Look for disconnected sections, holes, hanging insulation, dust streaks around joints.

Equipment too large = short cycles, doesn't run long enough to distribute air evenly. Equipment too small = can't keep up at peak load. Both cause unevenness.

Manual J load calculation determines actual heat load. Compare to equipment capacity. Most homes have oversized equipment from "rule of thumb" sizing.