Ducts are a critical part of making your home energy efficient, and a typical American home has 180 feet of ducts. If they're leaking air--which they almost always do--or if they're losing heat because they're uninsulated, they're contributing as much to global warming as they are to keeping you warm.
What You Should Know
- If you seal your leaky ducts, your furnace will heat your house more quickly and distribute the warm or cool air more evenly, and you'll greatly improve your indoor air quality by reducing the chances of dust, humidity, or harmful gases from gas appliances (such as a furnace, stove, or water heater) from entering your heating system and circulating to the rest of your house.
- A leaky duct system can also cause the air pressure in your home to decrease, sucking unwanted hot or cold air from the outside in.
- Even if the air isn't actually escaping from an uninsulated duct, you lose a lot of heat through its thin metal walls.
Easy Things You Can Do
First, check your ducts for air leaks. Hop into that crawl space or attic, or bring a flashlight to your heating vents, and start looking for disconnected, kinked, or crushed ducts as well as any gaping holes. If there's a room in your house that never gets warm or cold enough, lift off the vents in that room and use a flashlight to look for a disconnected duct. To detect small leaks, turn your furnace on and run your hand along the duct and ducts joints to feel for escaping air. Also, look for dirt streaks near the ducts' seams or on the insulation covering the ducts. Dirt indicates an air leak where dusty air has been escaping for years. You may also find peeling duct tape, exposed metal, or ripped outer covers, all of which could indicate a leak. Lastly, the most important place to check for leaks is where your ducts connect to your furnace.
Seal your leaky ducts. You can seal your leaky ducts on your own as long as you can get at the ducts easily, know how to use the sealing materials safely (read all directions!) and are aware of your local building codes (which tell you what kind of sealant you can use, etc.). How to seal your ducts if they aren't insulated:
- First, clean around the duct or duct joint
- Rejoin any disconnected ducts using duct ties, drawbands, or mechanical fasteners
- Seal the seams with water-soluble mastic sealant approved by Underwriters Laboratories or approved tape
- Last, insulate the ducts with 2-inch thick fiberglass
Caution: Don't use duct tape! Believe it or not, regular old duct tape should not be used to seal ducts, since its adhesive will dry out over time, causing it to peel or fall off. Even UL-181 (approved by Underwriters Laboratories, Inc.) or foil-faced duct tape is just a temporary fix. Also, simply insulating your ducts will not fix air leaks since insulation stops only heat flow, not airflow.
...Or hire a professional to deal with your ducts. Hiring a heating contractor or energy auditor may be more efficient to find and repair leaking air ducts than doing it yourself.
- Consider a duct blaster test. Although disconnected ducts are easy to spot on your own, it's best to locate small duct leaks using professional testing equipment. A professional will pressurize your duct system to tell you exactly which ducts are leaking and by how much.
- Consider sealing ducts with Aeroseal. A professional contractor can seal your air leaks quickly by closing all your vents then blowing high-tech adhesive particles, called Aeroseal, into your duct system. The particles stick to and fill up your leaks and is faster and more effective than sealing with mastic caulking or tape, and costs about the same as having a professional seal your ducts with mastic caulking.
Sources: 51 Easy Ways You Can Prevent Global Warming and Save Money, by Jeffrey Langholz, PhD, and Kelly Turner, and 30 Simple Energy Things You Can Do To Save the Earth, by PG&E