Duct Sealing and Insulation (Part 5 Home Energy)

If your ducts are entirely inside the thermal envelope, or conditioned area, this is typically not a problem. You can seal ducts in this situation to help balance your furnace. This becomes critical when you have ducts in a crawl space or attic. Any leaks in the ducts will help to heat that attic or crawl space. This can, of course, waste energy and create discomfort, but it can also lead to condensation issues, as the conditioned warm air hits the cool roof deck or crawl space. A very easy fix for sealing your ducts is to use duct mastic to seal up all the joints and connections on metal ducts. Mastic is good because it does not come off like tape and can expand and contract. It is a paste that can be spread with a brush or just an old glove that you are willing to sacrifice. Approved foil tape, not duct tape, can be used on fiberglass ducts.

Ducts in unconditioned spaces should be insulated to R-11. It is possible to lose 10-30% of a home’s heating and cooling energy through the conduction of un-insulated ducts.

sealing with duct mastic

ROI on duct sealing: AVG 14%

(Varies on fuel type, prices, accessibility, but also offers many residual benefits to the HVAC.)

ROI on duct insulation: AVG 22%

(Varies on fuel, prices, job difficulty.)

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