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How to Seal Furnace Gaps to Increase EfficiencyFurnace gaps can be caused by badly fitted sheet metal joints. Modern furnaces are frequently exposed to this problem since they often have separations in between the heat exchanger, the filter housing and the fan housing.

Unfortunately, gaps can create air leaks, reducing the efficiency of your furnace. To achieve optimum operating efficiency from your furnace, you’ll need to seal all furnace gaps. Almost anyone with some do-it-yourself experience can easily accomplish this task.

Regular silicone caulk can be used to seal smaller gaps in your furnace. You can run a bead along the gap, and use your finger to make it smooth. If the gap you’re sealing is located around the heat exchanger, you’ll need to use high temperature silicone caulk that won’t melt, while the furnace is running.

Larger gaps, especially ones around the filter air boxes, can be sealed with a foam type sealant. You can get this spray from any hardware store. Once the foam is sprayed into the gap, it expands and dries, sealing larger gaps that can’t be sealed by silicone caulk. Once the foam is nicely dried, you can use sandpaper and a knife to shape the foam sealant. You can even paint it to match your furnace color.

Aluminum foil duct tape can be used to seal all gaps. This tape has a strong adhesive, which is specially made to stick to sheet metal. Begin by removing all dust around the area with a damp rag. Then, wait until the area is completely dry. Apply the aluminum foil duct tape over the gap and press it firmly into place. The tape can be easily flexed, so it can even seal 90° gaps.

For more expert advice on how to seal furnace gaps to increase efficiency, please feel free to contact Aladdin Heating & Air Conditioning. We’ve been serving Southeast Michigan, and the Detroit Metro area since 1945.

Our goal is to help educate our customers in Warren, Michigan about energy and home comfort issues (specific to HVAC systems). For more information about sealing furnace gaps and other HVAC topics, download our free Home Comfort Resource guide.

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