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 betweenbuy used air conditioning units the device and the window frame, taping as needed.small window unit air conditioner reviews Why and How to Use a Timercost to replace air handling unit 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 Cool Extend the life of your AC system by keeping blinds or shades down during the day; you can also install awnings to shield south-facing windows from intense sun. Consider 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.Ductless split systems provide targeted heating and cooling comfort when conventional central HVAC equipment is too costly or impractical to install. Widely adopted in Europe and Southeast Asia, ductless technology continues to gain popularity in the U.S. as consumers and businesses look for cost-effective alternatives to window units, PTACs (packaged terminal air conditioners) and inefficient ducted systems. So, how does ductless air conditioning work?

In many respects, a ductless mini split operates in a similar manner to its ducted counterpart. In the refrigeration cycle, low-pressure gas is transformed into high-pressure gas by the action of a compressor. The heat is dissipated into the outdoors by the action of a forced air fan. The refrigerant then becomes a high-pressure liquid, and it is again changed into a low-pressure liquid by a metering device at the evaporator coil. Heat energy from the indoor air is absorbed by the refrigerant, and the resulting cooler air is pushed into the living area by the internal blower. The resulting low-pressure gas is moved through the suction line back to compressor, and the cycle is repeated again. There are two main elements in a ductless split system installation: The outdoor condensing unit houses three primary components including: How do ductless air conditioners work? It is important to recognize the distinct advantages of spilt system indoor fan coil units. Conventional central air conditioners employ a single air handler, blower and evaporator coil, which is usually installed in a garage or equipment closet.

A complex air distribution network provides an avenue for the delivery of conditioned air into each room of the building from a single point of origin. Unfortunately, ductwork is often inefficient, restrictive, dirty, leaky and noisy. Ductless indoor units include a fan and evaporator coil in the same enclosure. Each unit provides point of use air conditioning wherever it is installed. Stylish cabinets are available in wall mount, duct mount and ceiling cassette varieties. Whether used in single or multiple zone configurations, the indoor units can be strategically positioned to heat and cool one room or an entire building. The versatility and convenience of ductless technology completely eliminates the need for inefficient ductwork. When comparing ductless ac vs. central ac vs. window unit, ductless split systems are quieter, more efficient and offer greater levels of comfort. In multi-room applications, does ductless AC work? In fact, ductless air conditioners are an excellent choice for both single and multi-zone areas.

Systems can be installed in a variety of different configurations based on the following two platforms: Mini-Split: A mini split includes a single indoor fan coil and outdoor condenser. This combination is especially effective for cooling an individual room that has limited load requirements. If there is sufficient space to set multiple condensing units outdoors, several systems can be used in tandem to provide cooling for an entire building. This type of installation provides a separate temperature control for each unit. If there is a malfunction in one system, the rest will continue to provide conditioned air to the unaffected areas. Multi-Split: A multi-split system employs one condensing unit that is connected to several indoor air handlers. In this configuration, an indoor unit is selected and equipped with a thermostat. When there is a call for cooling, all of the units are activated simultaneously. This configuration is cost effective but should only be used in buildings where each room has a similar cooling load.

For true zoning in a multi-split application, a single condensing unit must be equipped with separate compressor circuits that are piped to each individual air handler. Every zone is controlled by a different thermostat, so the occupants can tailor the temperature to their individual preference. A Mitsubishi air conditioner designed for multi-split operation can include up to eight different zones. In the cooling mode, a ductless heat pump operates in essentially the same way as an air conditioner. The inclusion of a reversing valve allows the refrigerant to flow in either direction, which provides both heating and cooling from a single ductless system. When considering the installation of a ductless heat pump, it is important to understand the relationship between heating efficiency and the outdoor ambient temperature. In general, a heat pump operates most effectively in mild climates that rarely reach the freezing point. An electric heat strip can be installed to provide supplemental heat when necessary.