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Doing a little investigating before you start a ductwork project, can save you money now and for years to come.
Before we expose duct problems, we need a crash course on how your duct system works. Your air conditioner or heat pump works to cool and dehumidify the air, which is then sent through an air handler (fan). Ductwork extends out from your air handler, transferring the air down one or more main supply “trunks” with smaller “branches” coming off of them that are connected to your home’s registers. Return ducts extend from one or more large vents in the center of your home, or smaller ducts in each room, into the air handler to supply air for the fan to work. Think of it as your home’s circulation system with a heart, arteries, veins and capillaries.
Sounds pretty basic right? But a lot of things can go wrong that can make your home uncomfortable and expensive to cool.
“People just don’t think about their ductwork,” says energy efficiency expert Doug Rye. “And leaky ductwork can be a big energy waster.”
Proper sealing, insulating and airflow are the primary elements to consider as you investigate your duct system.
Investigating: Ductwork Leaks
Ready to expose your duct problems? Start with leaks. You might be surprised what a quick look at your ductwork tells you. After all, how often do you look at your ducts? The register of one room may have a duct only partially connected, or some of the duct may look crushed or contain holes, or the connections between the branches and trunk of your system may need to be re-sealed. If your ducts are covered with insulation, you may see a collection of soot on the insulation where it covers a loose connection, indicating a leak.
You can look and listen for small air leaks yourself, but it could get tricky. You might want to have a professional complete a blower door test. Though usually done to find air leaks throughout your home, the test could be modified to also estimate air leakage in ducts.
Eastern Illini Electric Cooperative recently added Duct Blaster service to its blower door testing. “We know that ductwork can be a serious problem,” says the co-op’s Manager of Marketing and Economic Development Bob Dickey.
If a home’s ductwork is located inside the conditioned space, in a heated and cooled area, then an ordinary blower door test is all that is needed. “Just because the ductwork is inside the building envelope, doesn’t mean that if it leaks it’s not a problem,” warns Dickey. He says that air flows to the path of least resistance and if you have leaks in supply or return ducts, the air will stay there, making some rooms colder than others. “And you wouldn’t know the reason for this unless you checked the ducts,” he says.
“One out of every three houses where the duct work is located in the attic has major leakage problems,” says Rye. Why? Well, for one thing, you probably don’t frequent the area much to see growing problems, and for another, the heat of an attic can speed up the deterioration of certain types of duct and sealant.
Speaking of sealant, duct tape, despite it’s name and though good for thousands of uses, doesn’t last long when used for ducts. Mastic sealant should be used for all seams and to repair leaks. You should also caulk all the points where your ductwork passes through your ceiling or floor. Make sure all connections are tight and well sealed. And don’t forget to check your return air ducts; it’s just as important they be airtight.
Investigating: Too Little Insulation
If your duct is located in an unconditioned space like your attic or un-insulated crawl space or basement, you’re going to need to insulate all of the ductwork to an R-6 level. Keep in mind, if you have metal duct, the insulation could be on the inside of the ductwork.
Rye says, “The hottest place in the United States in the summer is in your attic. Why would anyone put a cooling system in an attic? It beats me. And sometimes you can’t do anything about it.” He suggests that if your duct is located on the ceiling joists, you can have cellulose insulation blown over the whole system to save energy costs. But make sure your ductwork is well sealed and doesn’t have any problems first. It will be harder to access once it’s covered.
Check out your insulation to make sure there aren’t any gaps. Be diligent in your detective work, even small areas can lead to big energy losses.
Investigating: Bad Air Flow
If your house has uneven temperatures or uncomfortable humidity levels it could be a poorly designed duct system, something Dave Weidner, owner of Weidner Refrigeration in Divernon, says he often sees, even on new homes. “What’s happening is, people are buying these nice houses and can’t even live in them,” he says. He says airflow is very important, and to get the right air movement, you need to have the right sized duct, the right returns and the right dampers installed.
“It’s not rocket science, you just need to do the calculations. We will take a home and divide it up to determine the airflow for each room. We design the system so the air flow stays the same through that duct through the whole house,” Weidner says. He does this by properly sizing and locating supply and return ducts, adding dampers, and sealing the system well. He says a lot of people like the comfort level of radiant heat, and that’s because there is no airflow. But with a properly designed duct system, Weidner says you shouldn’t feel much air movement, or even know your unit is working.
One common mistake in many homes is a lack of return air ducts. Though ideally every room should have a return air duct, that isn’t the case in most existing homes. Many homes have just one return air register in the center of the home.
Rye says, “Ninety percent of all the return air systems I see are undersized and leaking.” He says one of the biggest failures of an air conditioning unit is the compressor, and undersized return air ducts that restrict airflow to that compressor. “You need about two square feet of return air grill space per ton of cooling. And most houses I see have exactly half of what they need,” says Rye.
One thing Weidner advises that you don’t want to do is adjust the damper on your register. “If you shut off the register damper you will slow down the airflow and affect the whole system, and the air won’t come out evenly in the rooms. You will also get a whistling noise effect.”
Dickey warns that flex duct can cause restricted airflow as well. “It’s a short cut, it’s easy and it costs less,” he says. “But you can either pay me now or pay me later, forever and ever.” Sometimes flex duct must be used in a duct system, but Dickey says it shouldn’t be more than 10 feet long. “It creates a lot of resistance and you’ll pay more for energy because it will take more work from your heating and air system to move the air,” he says.
The air needs to be flowing well through your filter as well, which won’t happen if you don’t change it frequently. Your filter may be located on your furnace or air handler, or in the return ducts. Check it each month during the winter and summer and change it when dirty, at least every three months. A dirty filter can cause compressor problems and shorten the life of your system, as well as damage air flow and air quality.
Your duct detective work may easily determine you have a problem, but to fix it, you will probably need to contact a qualified contractor in your area. Some technicians, like Weidner, are certified experts in duct design and installation. Your local co-op may be able to help you find someone in your area.
|Now that you’ve completed your ductwork detective work, it’s time to consider how your air conditioner’s efficiency affects your energy bills and comfort.
If your system isn’t very old, you may be able to improve its efficiency by simply keeping it clean and in the right location. Dickey says, “People let too much stuff grow around their air conditioning unit. And that does not allow the heat to dissipate as easily. Also, if the unit is exposed to the sun, you’re going to lose about 10 percent efficiency.”
Also, your system could be improperly sized. Bigger is definitely not better. “The biggest problem we see happening,” says Dickey, “is that our members just put in a bigger air conditioner. And the result of that is your system will cycle too frequently. You’re going to be cold when it’s on, the humidity control is going to be lousy and you’re not going to be comfortable.”
Weidner uses a car analogy to explain it to his customers, saying, “The unit has to run long enough to get the moisture out of the air. On a hot summer day it should run all the time. It’s like a car on the highway. You put it on cruise at 65 miles an hour and you get better gas mileage than stopping and starting and stopping and starting in town.”
Older air conditioners and heat pumps also have just one speed, making them less efficient and harder to size properly. Dickey says, “With the new two-stage geothermal and air source heat pumps, they run at the lower speed most of the time and it’s much more efficient. You’re going to hear it run more often, but it’s going to be more uniform and it’s definitely going to be more comfortable and less expensive to operate.”
You’ve probably heard on the news and read in this magazine that geothermal heat pumps are the most efficient heating and cooling systems. And when building a new home, it is definitely the best choice because you can stretch the initial costs out over the course of the mortgage. But in existing homes with air conditioner problems, it can be a costly renovation that some people feel they can’t afford.
“We’re highly recommending high-efficiency air source heat pumps to our members,” says Dickey. “Energy costs are not coming down. If they do, it’s very temporary,” he says.
Dickey recommends members buy a 15 SEER (Seasonal Efficiency Energy Ratio) or better air-source heat pump if replacing their air conditioning. “This is the year to get it done because of the tax credit. You can get up to $300 off your taxes but it’s over Dec. 31, 2007.”
For every SEER that you go up, it’s 10 percent better. So if you replace a 10 SEER air conditioner with a 15 SEER one, it will run 50 percent more efficiently. All new air conditioners must now be manufactured to a 13 SEER minimum, but make sure you are getting the most efficient model, as older, less efficient models are still available for sale. New geothermal heat pumps can be up to 22 SEER.
“If you have an air conditioner that is eight years old or older,” says Dickey, “it is likely between a 8 and 10 SEER. If you put in a high-efficiency 15 SEER air source heat pump, it will be 50 percent more efficient.”
The advantage of an air-source heat pump versus a standard air conditioner is also that you can use the system as your primary heating source this winter, keeping your existing furnace as backup for when temperatures drop below 15 degrees, or enabling you to switch from electric to gas heat depending on energy prices.
Again, sizing an air conditioner or heat pump correctly is key to comfort levels and efficiency. Just because you had a three-ton air conditioner before, doesn’t mean you should replace it with one the same size. Dickey recommends anyone replacing their system have a heat loss and heat gain analysis completed by the contractor. “We cannot stress this enough,” says Dickey. “The analysis determines how many BTUs of heating and cooling you really need.”
Contact your local electric co-op for more energy saving advice.