AC Losses Due to Duct Seals and Insulation Leaks in Your Heating and Cooling System

We’re rolling towards spring, which is followed by that certain hot weather season: summer in California. Two key points affecting AC efficiency can lead to a loss of your energy dollars and affect home comfort. Fortunately, they are relatively easy to remedy.

The First Common Cause of AC Efficiency Loss

Picture this: you’ve had an AC system in place for a number of years. At the time of installation, it was state of the art. You have had the system recharged when necessary; its output has been checked and seems to be up to par. It has worked well for you, and yet in recent years, you find that operation costs have definitely gone up and you’re at a loss to explain the recent loss of adequate home comfort. Before you blame it on global warming, read on. It could be something as simple as the trouble with older duct tape.


Traditional duct tape – The older, gray cloth-backed duct tape has been found deficient in standing up to normal use over a long period of years. It tends to break down and begin leaking. These leaks can be pouring your hard-earned energy dollars into attic spaces or other areas that are of no benefit. Modern techniques using a form of hand-applied mastic are proving to be very effective and more reliable. The mastic results in a 50 to 60% loss reduction. Even if you recently updated your AC unit, check with your HVAC specialist to see if they recommend a similar update of the ductwork.

A Second Predictable Problem Causing AC Efficiency Loss

As much as 30-40% of energy can be lost in poorly or non-insulated ducting. This is especially true when the ducting runs through un-insulated attics. Note that this is a loss through radiation, and not a leakage in joints.

Blown in insulation can compact, eventually losing efficiency, and can be moved around by air currents, animal activity, or human activity. Insulation wrapping can become dislodged or damaged from various sources, including that of animals chewing on it or making nests.

Other Points of AC Efficiency Loss Due to Insulation

Insulation is used for other areas besides ducting. In heat pumps for instance, key transfers of energy occur between the external heat pump and the internally placed cooling unit. Lines carrying the coolant are insulated to assure efficiency. Some of these lines may be exposed to sun and weather, or areas where mechanical damage, animal activity, rot or other degradation can occur.


Non-AC points of loss can be found around light fixtures, outlets, and poorly insulated walls, ceilings, floors, windows, doors and other parts of the house. Losses from these can cause your AC system to seem inefficient, though these areas are not directly a part of the home’s heating and cooling system in general.

Is Your Heating and Cooling System Delivering Full AC Efficiency?

Early systems used no sealing or insulation on ducts. Chances are this is not the issue, since taping of ducts has been ongoing for many years now, but in an older home, it is still a possibility. This is especially true if the system was installed or upgraded by a non HVAC professional with no training or experience in proper duct sealing and insulating.

Before the full heat of summer hits, arrange for an energy audit and testing of your ducts to assure you are getting full use of your AC system.

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