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Here’s Reasons Why You Shouldn’t Block Cold Air Returns

odour coming from furnaceYou’re probably committing one of the cardinal sins of HVAC efficiency without realizing it. While it can be tempting to block the cold air returns for rooms you’re not using to save energy or place furniture against them to arrange a room, blocking these registers is one of the most common ways to undermine your cooling and heating system.

What It Does

Blocking the return air supply to the air handler or blower compartment reduces the amount of air that flows easily into the system. The fan’s speed won’t slow any more when you close off the returns, and it creates positive air pressure.

Instead of easily pulling air from the closed-off return, it will suction it through any cracks and gaps it can around windows, exterior walls and doors. This brings in fresh, unconditioned air that will take more time to cool or heat, raising your energy bills.


Restricting the airflow in the air handler or blower contributes to premature system problems, which can be serious. When the system is set for cooling, too little air flows over the evaporator coil, the part that absorbs the heat from the air.

The refrigerant inside it will stay cold longer than it should, and the coil may freeze over. Besides losing the comfort the A/C provides, a frozen coil can cause water damage to the area around the air handler. If the system doesn’t shut off in time, the outdoor compressor may become damaged, leading to a replacement of this expensive part.

In the heating cycle, blocked cold air returns can cause the heat exchanger inside the blower compartment to store too much heat and eventually crack. If the cracks are too large, the furnace can emit carbon monoxide into your home’s air. Such a condition normally requires a complete system replacement. The discovery of any cracks in the heat exchanger is a serious issue and should prompt its immediate replacement.

The cold air returns are an essential part of an efficient and dependable HVAC system. It’s a good idea to check them periodically to make sure they’re not blocked and they’re clean. For more information, contact Arpi’s Industries, providing HVAC services for Calgary-area homeowners.

Our goal is to help educate our customers in Calgary, Alberta about energy and home comfort issues (specific to HVAC systems). For more information about cold air returns and other HVAC topics, talk to an Arpi’s technician today.

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