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Could restricted ductwork be causing uneven temperatures and short cycling?
I’m trying to determine whether my heat pump is actually oversized or whether the duct system is restricting airflow.
The house is approximately 1,600 square feet on one level, with a 3-ton heat pump serving three bedrooms, two bathrooms, a living room, kitchen, and hallway. The living room and hallway reach the thermostat temperature fairly quickly, but the two far bedrooms remain several degrees cooler in heating mode. In cooling mode, those rooms also seem to lag behind the rest of the house.
The system sometimes runs for only about 5–10 minutes before shutting off, then starts again later. However, on colder days it can run much longer. I’m wondering whether the short cycling could be related to low airflow across the indoor coil or poor return-air circulation rather than simply an oversized heat pump.
Some details that may help:
- The filter is a 1-inch pleated filter; I’m not sure of its exact MERV rating.
- There is one central return grille near the hallway, approximately 20 by 20 inches.
- The bedrooms have supply registers but no return grilles.
- Closing the bedroom doors makes the temperature difference
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1 reply
One caveat before blaming the heat pump: a closed bedroom door can pressurize the room if there’s no return path. That backpressure can reduce supply airflow, leaving the room cold while the central area satisfies the thermostat.
Check the door undercut and look for a transfer grille or jumper duct. As a practical test, compare temperatures with the doors open versus closed, or measure room-to-hall pressure with a manometer; a noticeable pressure difference indicates restricted return airflow. Also verify filter condition, total external static pressure, and airflow at the air handler. Only after those checks would I conclude the unit is oversized or short-cycling because of capacity.