The ENERGY STAR Web page you are looking for cannot be found in this location. Please try the following: If you typed the page address (URL) in the address bar, make sure that you spelled it correctly. Return to our home page. Use our site map to locate specific topics. Use the Search box above to locate the information you need. Ah, the sweet relief of a cool, dry house after a hot, sweaty afternoon of yard work. Like any mechanical system, AC needs a little TLC to run smoothly, including many tasks you can tackle on your own. We asked This Old House plumbing and heating expert Richard Trethewey to share his know-how for central air and window units. Why and How to Change Filters Dirty filters kill your AC's efficiency, so install a new one every month during the cooling season for central and window units (or clean them if you've got the washable type). Look for the filter's minimum efficiency reporting value, or MERV, which ranges from 1 to 12 for home AC units;

the higher the number, the better filtration it provides (and the more energy needed to pull air through it, so balance air-quality concerns with energy costs). Why and How to Fix Leaks Ducts can lose up to 30 percent of airflow through leaks, and window AC units are notoriously tough to seal properly. Find leaks using the old "smoke trick": For window units, light a stick of incense and hold it where the unit and the window frame meet; for central AC, hold the stick near duct connections. If the smoke blows around, you've got leakage. For ductwork, use foil tape to seal small gaps and duct mastic for larger ones; for window AC units, stuff foam between the device and the window frame, taping as needed. Why and How to Use a Timer There's no need to blast the AC at full tilt while you're at work. For central units, install a programmable thermostat that lets you set higher temps when you're gone and cooler temps when you're home. Newer window units have built-in timers and adjustable thermostats, or you can buy a timer at any home store for $10 to $20;

just make sure it matches your device's voltage. Unless you're going on vacation, don't shut off the system; otherwise, the air compressor will need to work harder to cool your house later. Ducts in hot attics or crawl spaces should be wrapped to keep the air within them cool. You can use spray foam, batt insulation, or rigid-foam insulation. Seal batt and rigid insulation with foil tape (not duct tape). For tight spaces, wraps like Reflectix offer some degree of insulation. Why and How to Service Compressor/Condenser A central AC system's air compressor and condenser are usually located outside the house, close to your foundation. It works best when there's about 24 inches of clear space in all directions, so get rid of nearby shrubs, tall grass, leaves, and hanging branches. TOH Tip"Install condensers or window units on the north or east side of your house, or build a screen to shield them from the sun. Putting them in direct sunlight reduces their efficiency by as much as 10 percent."

—Richard Trethewey, TOH Plumbing and Heating Expert Why and How to Keep Unit Coolac unit insulation Extend the life of your AC system by keeping blinds or shades down during the day; used 40 ton ac unityou can also install awnings to shield south-facing windows from intense sun. what is outdoor ac unit calledConsider running the AC in conjunction with floor or ceiling fans to circulate cooled air more effectively. Why and How to Maintain Unit The dealer who installed your central AC (or one you find locally) should put you on a yearly cleaning schedule that goes beyond just cleaning the filters. Schedule this checkup before the cooling season starts (or do it now if you didn't do it earlier this year), and make sure it includes the following tasks: cleaning and inspecting coils;

cleaning or replacing filters; adjusting and replacing fan belts; lubricating motors and bearings; cleaning and checking blowers and fans; inspecting controls and safeties; checking refrigerant and pressures; and verifying operating temperatures. Why and How to Get Airflow Shutting too many interior doors causes central AC systems to go out of balance, meaning there's less airflow in the entire house. If you want some privacy, keep doors slightly ajar instead. Why and How to Upgrade Federal laws require AC units to be a lot more efficient than they were just 10 years ago. For central AC, look for the seasonal energy-efficiency ratio, or SEER; for window units, the measure is simply called the energy-efficiency ratio, or EER. The standards mandate a SEER of 13 and an EER of 8, but devices with higher numbers will cost less to operate.Jeff Wilson replaced his HVAC system for the same reason most homeowners do: It broke. Five years ago in the heat of summer, his air conditioner died — and this was well before he embarked on an all-out Deep Energy Retrofit (DER) to green his 70-year-old Cape Cod.

Still, he used this opportunity to upgrade the old, standard unit. "We had to keep a little air conditioning on so we didn't have so much mold," Jeff says, describing a major pitfall of the home: high humidity that produced damaging condensation, causing woodwork deterioration and poor air quality. Jeff got three bids for the HVAC project, ranging from $3,500 to trade the old HVAC unit for a comparable model to $12,000 for a state-of-the-art system. (These price estimates are from the time of installation in 2005.) "We expected gas prices to go through the roof, which they did in 2008," Jeff says, weighing the options. "And we expected this new HVAC unit to last." The 26-year-old unit Jeff replaced was 80 percent efficient — not bad for 1979 technology. But we've come a long way since then. The standard option Jeff considered as a replacement would basically restore the system to status quo for $3,500. But Jeff was looking for more. The midrange unit was priced at $4,200 and would boost the furnace efficiency to 90 percent, with a 16-SEER air conditioner.

The lower the Seasonal Energy Efficiency Rating (SEER), the more energy it takes to cool the home. The high-end system would cost Jeff $5,800, but for that $2,300 more, he got more features and optimum, 97 percent efficiency. Because the Wilsons mainly used their air conditioning to defuse the thick humidity typical in southeast Ohio during summer, a variable-speed blower was worth the investment. This mechanism allows Jeff to set the humidity level on his thermostat. "Instead of cooling your house down to get humidity levels low, you can do a bit of dehumidifying [with the blower] to keep the temperatures lower," he explains. Jeff could get this feature plus 7 percent more efficiency on the gas furnace. "We were looking toward the future," he says of the price tag and, when comparing systems, the estimated five-year payback. The choice was relatively easy for Jeff. He chose the highest-end unit and sized the HVAC system exactly to fit his home so no energy would be wasted.

However, he did not figure in extra capacity to supply heat and air to the new home addition, which would come to fruition five years later. Because this addition is built using the latest green technology in new construction — and solar panel energy — he doesn't expect to need the extra power for this part of the house. Immediately after installing the new HVAC, Jeff noticed energy bills that were about 20 percent lower. "That's pretty significant," he remarks, noting that as HVAC systems age they become less efficient. The old system was probably running at 50 percent efficiency by the time it was replaced in 2005. Invest in the best. "This is a long-term decision; it's not an appliance like a microwave," Jeff says. "By buying the highest efficiency rating possible now, you hedge your bets against the high energy prices that will come later."It may sound like a good thing if an HVAC unit kicks on and cools down a house in five minutes. "If you put in a unit that's too big, you'll fry the compressor," Jeff says.