Duct Sealing for Energy Savings and Improved Comfort

Jun 17, 2010 | Energy Efficiency, Air Quality

Snapshot | About Your Ducts | Duct Testing | Rebates | Take action!

Snapshot

Although we don't think about our ducts much (out of sight, out of mind), pay attention to your ducts when considering home improvements. Duct performance has a big impact on energy savings and on comfort. Ducts should be a top priority when making your home green.

Ducts are the long "tubes" that deliver hot air from your furnace, and cold air from your air conditioner, to your living spaces. Ducts leaks cause three major problems. First, not enough air arrives in a room, leaving it too hot, or too cold. Second, the leaks introduce air with moisture and particulate, lowering indoor air quality. Third, the air leaking through the ducts -- that air you just spent money to heat or cool -- becomes waste as it flows into your attic, crawlspace or walls.

Duct sealing can be a straightforward - although dirty - job when you have access to the ducts. But don't use duct tape to seal your ducts! Duct tape bakes as heat flows through the system, and will dry out and flake off within a year or two. A better sealant is mastic, an adhesive paste. But, because sealing ducts is such a messy job, most homeowners will want to call in a pro. That's a great idea, because they can also test the systems and use the data to improve performance.

About Your Ducts

Duct systems are divided into a supply run, the tubes that take heated air from your furnace to the individual rooms in your home, and a return, a smaller set of tubes that suck in air from your indoor area through a few large grates and deliver it back to the furnace for re-use. Typically there are one or two large ducts for the returns. Ducts can be located in attics, crawlspaces and inside walls, and the supply and return runs can be split between locations.

Here are two significant air leaks that are not uncommon in Bay Area homes:

If your ducts are in the attic and you run central air conditioning, then any duct leak will significantly increase your energy bills. Attics get very hot in the summer (up to 140° F), so when your return duct goes through the attic and leaks in that hot attic air, your air conditioner is working much harder. When supply runs are in the attic, air leaks waste your cooled air. The result? Your air conditioner stays on much longer. If your return duct has an air leak, indoor air quality suffers. Return air ducts are larger, so with an air leak in the return your heating and cooling system is efficiently spreading around the moisture, particulates and other grime that is in your attic or crawlspace into the rest of the home. If your ducts or furnace are in the garage, air leaks can introduce car exhaust into your home.

Leaky return duct in garage evidenced by discolored insulation. Photo: WattzOn

Another area of common air leaks is around the furnace. Often the ducts are attached to the furnace via wall cavities lined with sheet metal, or specially constructed metal/plywood boxes. Both of these are big sources of air leaks.

As you get ready to seal your ducts, also consider duct insulation. If your ducts are in the attic, in the summer they'll get too hot from the surrounding air. Duct insulation will make your house cooler. If your ducts are in your crawlspace, they'll get too cold in the winter. If you are replacing your ducts, your installer may use duct tubes that are pre-insulated by the manufacturer.

Your installer may also want to talk to you about moving your ducts or replacing them. Often duct systems have not been correctly sized for energy efficiency or comfort. Rather than seal a system that doesn't perform well, the installer may suggest you simply replace your ducts. The labor for install can be cheaper in some cases. (If you are considering replacing your ducts, also take a look at your insulation and performance of your furnace and air conditioner. They work as a system and you'll want more information on how your system is performing. A home performance contractor can help.)

Want to talk over your options? Have questions? Speak with a WattzOn Green Home Expert for free. Call 1-800-314-5997. Duct Testing

Energy auditor performing duct test. Photo: WattzOn

Duct testing is standard in energy audits. There are several types of tests to get an estimate of how well your ducts are performing and how any air leak affect your comfort.

Duct Blaster™ tests. This test is based on sealing off all air exits in your ducts, gently pressurizing the system, and then measuring the amount of air leakage. You'll see your energy auditor taping over all your duct grates and registers to seal off the system. Then they'll attach a large measuring device to your return grate. The Duct Blaster™ test result can tell you 5% of the air heated by your furnace leaks out of your ducts, 25% or more. 15% leakage or less is considered very low for existing California homes.

Flow hood tests. This test can also be done by your energy auditor. A simple hood with a measuring device is placed over a furnace register while the furnace is on. The flow hood measure the rate of air flow coming out of the register. This data can help to identify duct areas with large leaks or obstructions, or design problems in the original duct layout.

General flow and pressure testing. Some heating and cooling professionals prefer to test your duct system under normal operating conditions. They'll measure air pressure at various points and air flow while the furnace is operating. These test results help to determine if the system can send the proper rate of air flow to each room.

The test results, plus your installer's expertise, can help you get an overall picture of the status of your ducts. How much air is leaking? Where? Is sufficient air being delivered to each room? Is too much air being delivered to some rooms? Will repairs and minor adjustments improve air quality?

Duct sealing is a great way to get more years of service out of your duct system. It is relatively cheap and can be an effective way to improve home performance.

Rebates

Incentive Source

Rebate Summary

Getting Started

Federal Tax Credit None

Alameda Municipal Power

None

City of Palo Alto Utilities

None

Pacific Gas & Electric

up to $200

Details

Silicon Valley Power

None

Take action!

Repair, seal up, or replace ducts

Want to talk over your options? Still have questions or concerns? Want to find a quality contractor?

Speak with a WattzOn Green Home Expert for free. 1-800-314-5997

We are your free, independent, qualified, green home energy experts. We don't sell windows, furnaces or insulation or anything else for that matter, and while we can recommend products, we don't get paid by manufacturers. What we do provide is informed, expert and unbiased guidance on your best and most-effective opportunities to save energy, save money and make your home more green. WattzOn can also connect you to our network of qualified and verified local green home energy auditors and green home contractors who do great work.

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