Problems After AC Replacement
A new unit's efficiency rating describes what the equipment does with the electricity it uses, not what actually reaches the house. If ducts leak conditioned air into an attic, airflow is restricted, or the home's cooling load is higher than expected, the system runs longer to compensate, and the expected bill reduction from a more efficient unit gets offset or erased entirely.
If a meaningful share of conditioned air escapes through leaky ductwork before reaching the rooms, the system has to run longer to deliver the same comfort, consuming more electricity than the unit's rating would suggest.
A dirty filter, undersized return, or restrictive ductwork reduces the air the equipment can move per cycle, requiring extended runtime to reach setpoint and increasing energy use accordingly.
If insulation, windows, or occupancy patterns were not part of the sizing decision, the equipment may be working against the same (or a larger) load than the unit it replaced, regardless of its efficiency rating.
New equipment that is undercharged, overcharged, or has an incorrectly configured blower profile can run well below its rated efficiency, even though the equipment itself is capable of much better performance.
A lower setpoint, extended occupancy, or added humidity control settings can increase energy use independent of the equipment change, and are worth ruling out before assuming a system fault.
Comparing bills across different months or after a utility rate change can create the appearance of a problem where usage patterns are actually similar.
Stick to what you can see, feel and hear. Leave electrical panels, refrigerant, combustion appliances and equipment internals to a licensed professional.
A unit's SEER2 rating is measured under controlled conditions at the equipment itself. It says nothing about what happens between the equipment and the register. Duct leakage subtracts delivered cooling without subtracting energy use, since the equipment still runs and still consumes electricity to produce air that never gets used.
In homes with ductwork routed through hot attics, leaked conditioned air is also frequently replaced by hot attic air pulled in through return-side leaks, adding load on top of the loss, both of which increase runtime and cost.
Duct Daddy specialises in duct leakage testing and duct sealing. We do not perform mechanical HVAC repair, refrigerant work or equipment replacement. Contact a qualified HVAC contractor if any of the following apply:
Long, humid cooling seasons in this region mean any efficiency loss from duct leakage or airflow restriction compounds over many months rather than a few, making the gap between rated and actual performance more visible on the bill.
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A duct leakage test measures how much of your new system's output is being lost before it can do any cooling — a direct answer, not a guess.
New equipment fixes what's inside the cabinet — it does not automatically fix distribution, sizing, or envelope issues elsewhere in the house.
Long runtime after a replacement can be normal variable-speed behaviour, or a sign the equipment is fighting a load or duct problem.
Yes, leaking supply and return ducts can raise energy use — but the size of the effect depends on where the leaks are and how the ducts are routed.
A gradual increase in runtime usually points to a gradual loss somewhere — capacity, delivery, or load — not a single sudden failure.
What sealing can and cannot fix, and how to know if your duct system is a good candidate.
New equipment doesn't change the ducts, the load, or the envelope — and any of those can leave a house hot.
Browse every symptom in the troubleshooting center.
Schedule a duct leakage evaluation and get measured numbers for your home — not a guess.
