How much runtime increase is normal as a system ages?

There's no fixed figure worth quoting, since it depends heavily on maintenance, climate, and system design. What matters is comparing runtime on similarly hot days over time rather than assuming any change is abnormal.

Can duct leaks really get worse over the years?

Yes. Duct connections sealed with mastic or tape are exposed to repeated attic heat cycling, and flex duct can sag or separate slightly at boots and collars over time, gradually increasing leakage.

Should I get the refrigerant checked first or the ducts?

Either is reasonable, but they answer different questions. A refrigerant and coil check by an HVAC contractor addresses capacity; a duct leakage test addresses delivery. Doing both gives the clearest picture.

High Energy Bills & Long Runtime

Why Is My AC Running Longer Than It Used To?

A gradual increase in AC runtime usually reflects a gradual loss of capacity or delivery rather than a sudden failure. Common causes include a dirty condenser or evaporator coil, aging refrigerant charge, a duct system that has developed leaks or separations over time, and rising heat load from attic insulation settling or added heat sources. Comparing runtime on similar-temperature days helps separate real decline from normal weather variation.

Key takeaways

Compare runtime on similarly hot days across years, not just week to week.
Gradual decline points to gradual wear: coil fouling, aging charge, duct seams working loose.
Duct connections and mastic can degrade with attic heat cycling over years.
A sudden jump is more often mechanical; a slow creep is more often cumulative.
Measurement separates equipment decline from duct loss more reliably than guessing.

Most likely causes

Gradual coil fouling

Both indoor and outdoor coils accumulate dust, pollen, and grime over seasons of operation. This is a slow process that quietly reduces heat transfer and increases runtime year over year.

Refrigerant charge drifting low

A small, slow leak can reduce charge gradually rather than all at once, producing a creeping decline in capacity rather than a sudden failure.

Ductwork loosening or separating with age

Mastic, tape, and mechanical fasteners on duct joints are exposed to attic heat cycling year after year. Connections that were tight at installation can loosen or crack over several summers, gradually increasing leakage.

Insulation settling or being disturbed

Blown attic insulation compresses and shifts over time, and can be pushed aside during other attic work, gradually raising the heat load the system has to fight.

Blower or fan performance declining

Bearing wear, belt slippage (on older systems), or a fan motor running below spec reduces airflow gradually, which shows up as longer cycles for the same result.

Filter or airflow habits changing

A switch to a higher-restriction filter, or simply longer intervals between changes, can produce a slow airflow decline that mimics equipment aging.

Added heat sources in the home

New electronics, an added room, or changes to window coverings and landscaping shade can raise the load the system has to meet without any equipment or duct change at all.

What you can safely check yourself

Check your filter-change interval and confirm it hasn't lengthened over time.
Compare recent runtime to the same month in a prior year, on similarly hot days.
Look at supply registers to confirm none have drifted closed.
Visually check the outdoor coil for a buildup of dust, pollen, or grass clippings.
Note whether the decline was gradual over seasons or a step change after a specific event.
If you can safely view attic ductwork, look for visible gaps, disconnected sections, or sagging insulation near duct runs.

Stick to what you can see, feel and hear. Leave electrical panels, refrigerant, combustion appliances and equipment internals to a licensed professional.

What a professional should measure

Refrigerant charge verification against manufacturer specification.
Coil cleanliness inspection, indoor and outdoor.
Static pressure and airflow measurement at the air handler.
A duct leakage test to establish whether leakage has increased since installation.
Blower motor and fan performance check.
Temperature split across the evaporator coil.

When duct leakage could be involved

Duct connections are not permanent by nature — mastic and tape are materials that age, and mechanical strapping can loosen as flex duct sags over years of attic heat cycling. A system that was well-sealed at installation can develop measurable leakage several years later without anyone touching it.

Because this happens slowly, homeowners often notice the runtime creep before they notice any single dramatic symptom. The bill or the runtime rises a little each summer rather than jumping all at once.

A duct leakage test at this stage establishes a number you can compare to what a healthy system should be losing, rather than guessing whether age has caught up with the ducts.

When this probably isn't a duct-sealing problem

The change happened abruptly rather than gradually, which is more consistent with a mechanical fault or refrigerant leak than duct aging.
Airflow is uniformly weak at every register rather than uneven, pointing toward the coil, filter, or blower.
You hear new or unusual noise from the outdoor or indoor unit.
The system is well past its typical service life and multiple components are aging together.

When to call an HVAC contractor

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:

Runtime jumped suddenly rather than gradually.
You suspect a refrigerant leak or notice reduced cooling alongside longer runtime.
The outdoor coil or fan shows signs of mechanical wear.
The system is old enough that several components could be failing at once.

Why this matters in Southeast Louisiana

Attics in Southeast Louisiana cycle through some of the widest temperature swings a duct system will see anywhere, which accelerates the aging of mastic and tape joints over multiple summers.

Because the cooling season here is long, a slow decline that might take years to notice in a milder climate can show up within a couple of summers locally.

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Frequently asked questions

How much runtime increase is normal as a system ages?: There's no fixed figure worth quoting, since it depends heavily on maintenance, climate, and system design. What matters is comparing runtime on similarly hot days over time rather than assuming any change is abnormal.
Can duct leaks really get worse over the years?: Yes. Duct connections sealed with mastic or tape are exposed to repeated attic heat cycling, and flex duct can sag or separate slightly at boots and collars over time, gradually increasing leakage.
Should I get the refrigerant checked first or the ducts?: Either is reasonable, but they answer different questions. A refrigerant and coil check by an HVAC contractor addresses capacity; a duct leakage test addresses delivery. Doing both gives the clearest picture.

Establish a current duct leakage number

A duct leakage test tells you whether your ducts have loosened over the years, giving you a measured baseline instead of a guess.

Schedule a Duct Leakage Test

Find out what your duct system is actually doing.

Schedule a duct leakage evaluation and get measured numbers for your home — not a guess.

Schedule a Duct Leakage Evaluation