Uneven heating or cooling between rooms
easy 1–2 h
Tools: thermometer, flashlight, screwdriver, tissue or incense stick · Materials: HVAC filter, foil-backed duct tape (not cloth duct tape)
Steps
- Open every supply register and move furniture, rugs and curtains off them; a closed register in one room starves the rooms downstream.
- Replace the filter and note the airflow at each register with a tissue — weak flow in the far rooms with strong flow near the unit points at leaky or crushed ducts.
- Find the damper handles on the ducts near the furnace or air handler and turn the far rooms' dampers fully open and the nearest rooms' partly closed.
- In summer, run the fan on 'on' rather than 'auto' for a week to mix air between floors; in winter, set ceiling fans to spin clockwise on low.
- Inspect exposed ducts in the attic or basement for gaps at joints and boots, and seal them with foil tape or mastic — not cloth duct tape, which dries out.
- Measure the temperature in each room at the same time of day for three days to see whether the balance has improved.
Stop and call a pro if
- the temperature gap is more than 5 °C (9 °F) after balancing — the system may be undersized or a zone is not working
- a room over a garage or with a vaulted ceiling never reaches temperature — that is an insulation problem
- the ducts are crushed, disconnected or show mould inside
What a pro does that you can't
An HVAC technician measures airflow at every register, seals and rebalances the duct system, and can add a zoning damper or a mini-split for the room the ducts cannot reach.
DIY cost: $10–30 in a filter and foil tape