Attic Central Air Conditioning: Energy Efficiency Information

A thermal image of an attic air handling unit for a central air conditioning system.
A thermal image of an attic air handling unit for a central air conditioning system. | Source

Using thermal imaging is a very useful tool to find moisture, insulation, and even electrical issues. While it is not a perfect technology, it does offer the ability to accurately show another party that there is an issue and where the issues are along with the advice of how to correct these issues. This article will focus on attic air handling units and the energy efficiency of these units from an air leakage and distribution standpoint.

Air Handling Unit

The air handling unit is composed of a blower motor that turns on by a signal sent from a thermostat or a relay switch. The fan then blows air across a coil that either gets hot or cold. In this case, the coil is an evaporator coil that an exterior condenser unit cools using freon gas. The illustration below demonstrates the cooling cycle of a standard central air conditioning system.


Air conditioning - schematic of system
Air conditioning - schematic of system | Source

As you can see from the thermal image of the air handling unit, there is a significant amount of heat escaping from the connections of the unit to the duct work. This is a concern in areas where the climate changes drastically from season to season. In hot climates, this type of leakage could reduce the efficiency of a cooling system by mixing in hot air that is pulled from the attic into the duct work through these leak points.

Solutions

The simplest solutions involve checking all of the duct work connections to the air handler and making sure that they are properly sealed with metal HVAC tape or closed cell spray foam.

The duct lines should also be insulated with a water resistant vapor barrier over the insulation that encapsulates the duct work. If none exists, using close cell spray foam to cover the ducts and seal the joints is the easiest way to achieve proper R-value and duct sealing, but is also the most costly. Duct wraps can be purchased for a fraction of the price, but take a lot of work to properly install on an existing system.

If you live in an area where the temperature changes drastically, you should replace the filter of the air handler with a piece of foam board insulation in the wintertime. Simply taking the filter out and putting in a same sized piece of foam board prevents heat from escaping into the attic.

Warnings

Do not run your air handling unit without a filter or with a piece of foam board in the filter spot. This could not only damage your air handler unit, but cause a build up of dust and allergens.

Attic air handlers should be inspected every year but no less than every 3 years to make sure that no freon leaks or ice buildup is occurring. Always consult a licensed HVAC technician before tampering or attempting to work on an air handling unit.

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