The best air conditioner is the one you don’t have to think about. It comes on the moment the indoor temperature rises above the level you have set on the thermostat, and then runs quietly and efficiently when needed. But no system lasts forever and, when it’s time to perform routine maintenance, make repairs or replace your system, it’s helpful to understand how an air conditioning system works and what other options are available to cool your home.

A typical central air conditioning system is a two-part or split system that includes:

• An outdoor unit containing a condenser coil, compressor and a fan.

• An evaporator coil, usually installed on top of the gas furnace inside home.

• A series of pipes, or refrigeration lines, connecting the outside and inside units.

• Refrigerant, the substance in the refrigeration lines that cools the air circulating through the units.

• Ducts that transport the conditioned air to the various rooms inside your home.

• A thermostat or control system to set your desired temperatures.

A cooling system works much like the circulatory system in the human body. Warm air from inside your home is pulled into ducts by a motorized fan through a return vent in the wall. Using electricity as its power source, refrigerant is pumped from the compressor coil in the outside unit to the evaporator coil inside your home, where it absorbs the heat from the air. The cooled air is then pushed through the ducts to vents throughout your home, lowering the interior temperature. This system creates a continuous loop that cools your home.

A good quality, high efficiency central air conditioner delivers a number of benefits:

• Helps keep your home cool in warmer months, while reducing humidity levels.

• Provides cleaner air inside your home;

• As your central air conditioning system draws air out of the rooms through return air ducts, the air is pulled through an air filter, removing airborne particles such as dust and lint. The filtered air is carried back to the rooms via supply ducts.

In the winter, cold air inside the home is pulled into the “return” duct and transported via ducts through the blower system and into the heat exchanger. The air is heated as it passes through the heat exchanger and is then returned to the various rooms through the supply ducts.

The efficiency of a gas furnace is measured by the AFUE rating, which stands for Annual Fuel Utilization Efficiency. AFUE measures the efficiency with which a system uses fuel to generate heat. A high AFUE rating indicates that your system    is minimizing waste when heating your home, resulting in a more efficient system. The more efficient your system, the less fuel it takes to heat your home. And that translates into lower heating bills during the winter.

For example, a furnace with an AFUE rating of 80% means that 80% of the fossil fuel used is being converted to heat, while 20% escapes and is wasted. Many older furnaces have AFUE ratings of as low as 56%, which means that almost half of the energy used to generate heat is lost in the process. The most efficient gas furnaces exhibit AFUE ratings as high as 98%, meaning that only 2% of the fuel is lost when producing the heat. That’s why switching to a newer, more energy efficient gas furnace can result in meaningful cost savings over time.

There are basically two types of gas furnaces: condensing and non-condensing.

Condensing Gas Furnaces

• Use a second heat exchanger to heat the air from condensed exhaust gases in order to reach higher efficiencies.

• Can achieve AFUE ratings as high as 98%, with only 2% energy loss when producing heat.

A modulating gas furnace is a type of condensing furnace that runs at a slower pace, allowing the system to maintain a set temperature with fewer variations in temperature throughout the day. This type of furnace is more expensive, but maximum comfort has a price.

Non-Condensing Gas Furnaces

• Are less efficient, typically around an 80% AFUE rating.

• The gases are vented out of the home, rather than used to produce more heat.

In some gas furnace models, you can choose between a single stage and two stage option. A single stage furnace runs at full speed and then turns off when the system recognizes that it has achieved the desired temperature. Conversely, it turns on when the air falls below the desired temperature. This type of system tends to be less efficient because of the energy required to turn the system on and off and because the temperature needs to rise above or below the desired temperature before the system will turn off or on, respectively. With a two stage system, the furnace runs at high speed only if the air is more than 2 degrees off the set temperature. Once it is within that range, it switches to slow speed, which uses less energy. A modulating gas furnace, described above, is the most efficient model because it runs continuously, does not go above or below the desired temperature and is quieter.

A heat pump switches from cooling mode to heating mode by“reversing” the refrigeration cycle. As described above, in cooling mode, the system pulls hot air from the rooms inside the home and passes the air over an evaporator coil filled with a refrigerant that absorbs the heat. In heating mode, the system pulls air from outside the home into the condenser, where the coil uses refrigerant to absorb the ambient heat from the air.  That’s right, even cold air contains ambient heat. Cold air from the rooms is then passed over the coil, heated and returned to the rooms via the supply ducts. The refrigeration cycle continues until the temperature reaches the desired level, as set on the thermostat.

Heat pumps are most effective in warm and moderate climates, where heating is  not a priority. That’s because, when temperatures fall below freezing, the amount of ambient heat in the air is not sufficient to heat your home. That’s why furnaces are more popular in northern climates. You can, however, supplement a heat pump with a heat strip. A heat strip is an electric coil that operates like a small space heater. It will produce additional heat when needed. Heat strips can also be added to air conditioners.

Another advantage of a heat pump is that it can work with a ducted system or as a “ductless” system. If your home does not have ductwork, or if you are adding on a room and don’t want to spend the money to install ducting, a heat pump can work with an air handler installed in each room to be conditioned. While this may not be the most attractive option, it can save you a lot of money.

The efficiency of heat pumps is measured by HSPF, which stands for Heating Seasonal Performance Factor. A higher rating indicates greater efficiency in heating your home and thus greater savings on monthly energy bills.

Packaged Units are heating and/or cooling systems in which all of the components are housed in a single “box”, located outside the home. This makes packaged units ideal for situations in which indoor space is tight. However, while they meet minimum efficiency standards, packaged units can not match the performance of high efficiency split-systems (where there are separate components inside and outside your home).

Packaged units are available in a variety of combinations:

• Packaged air conditioners, which can be combined with heat strips to  produce limited heat (meeting the needs of homeowners in warmer climates who need heating only on rare occasions.)

• Packaged heat pumps.

• Packaged Gas-Electric.

• Packaged Dual-Fuel units that combine a gas furnace with a heat pump. The Dual-Fuel unit is particularly popular in regions that experience both mild and cold winters. When temperatures are mild, the heat is produced by the heat pump. When temperatures drop below freezing, the gas furnace takes over.

While component systems tend to be more cost efficient over the long term, if you are replacing an existing packaged unit, the cost of converting to a component system can far outweigh the monthly cost savings. Of course, this will depend on various factors such as the cost of utilities in your area and how long you intend to stay in your home.

An HVAC system works much like the circulatory system that pumps blood though the body from the heart. An HVAC system does this through the use of ducts. Supply ducts are rigid or flexible metal tubes that run from the air handler into as many rooms of the home as necessary. There is a separate “return” duct that returns the air from the rooms to the air handler. The condition of the ducts can impact the effectiveness of your HVAC system. If there are leaks, or if your existing ducts are filled with dust and debris, they may need to be cleaned or replaced, at an additional cost.

Vents control how the air is dispersed from the ducts into each room. Vents typically are located in the walls, floor or ceiling and have louvers that allow you to control the direction and amount of the air flow. The location of the ducts and vents is critical to their functionality. It is based largely on the construction of your home (where can ducts be installed), but can have a significant impact on the efficiency of your system. The wrong size duct, or placing ducts in the wrong location, will significantly reduce the efficiency of your system, and more importantly affect your comfort. That is why it is so important to have your system specified and installed by a certified professional.

Filters are used to prevent dust and debris from getting inside the HVAC system, as well as to improve the air quality in your home. Filters are typically located next to the Air Handler or inside the “return” vent. Filters help to keep your HVAC system functioning more efficiently by catching debris that would otherwise flow into the system. That is why filters need to be changed on a periodic basis. As debris builds up, it restricts the air flow into the system, reducing the systems’ efficiency.
Changing your filters at least twice a year is recommended to keep your system running smoothly (although the need to change filters is impacted by the number  of people in your home and other factors, so having them checked regularly won’t hurt). There are many different types of filters in the marketplace, some of which can significantly improve indoor air quality, which is important if you have allergies or other illnesses. A certified HVAC technician can help you determine what filters are right for your home.

• Thermostats allow you to control your HVAC system. 

• You can set specific temperatures by day, or time of day.

• Can result in lower energy costs because your system will turn off when it isn’t needed.

A thermostat works by reading the temperature in the room in which it is installed. It recognizes when the temperature drops below (in winter) or rises above (in summer) the desired temperature for your home. The thermostat then triggers the HVAC system to turn on and bring your home back to the desired temperature. For these reasons, the location of the thermostat is very important. For example, if it is located on a wall that gets a lot of sunlight, it might assume that the temperature is warmer in the home that it actually is.

Today, with advanced technology, you can purchase thermostats that can be controlled wirelessly from your cell phone or tablet, making controlling your home environment very convenient. No more getting out of bed to turn the heat down in your kids’ room or worrying about forgetting to turn the system off when you leave for vacation. You can control your HVAC system from anywhere that has internet access.

Zones allow you to customize the temperature in different rooms in your home using a single HVAC system. Zones are created by installing a “baffle” inside the duct, which controls air flow into that duct. A separate thermostat is required for each zone. However, this eliminates the need to install multiple systems. For example, you could create one zone for your upstairs bedrooms and another for your downstairs living quarters. This will allow you to set different temperatures for each zone, using the same system. This also makes your system more efficient, because you can control the temperature settings by room. For example, it takes more heat to heat a wide open area, like a family room, than it does to heat an office. You would want to create a separate zone for each so that, for example, you can heat your office without having to heat your family room.

Indoor air quality can be greatly improved with a good heating and cooling system. A study by the Environmental Protection Agency found that the level of air pollutants “indoors” is often higher than the level outdoors. Most homes are riddled with some or all of the following: mold, mildew, bacteria, pet dander, dust mites, pollen, viruses, skin flakes, and chemicals. A ducted air conditioning and/or heating system uses filters to remove some of the pollutants. There are also air purifying systems that can be added to your HVAC system to provide additional air purification.

It is important to have the “right” size unit in your home. Furnaces and Condensers come in different sizes. Larger units are needed to heat homes with larger rooms and higher ceilings. Units that are too small will need to stay on longer to keep your home at the desired temperature, or may not be able to achieve the desired temperature at all. Systems that are too large will turn off too fast, stopping air circulation, which can reduce your indoor air quality and lead to potential issues like mold. Only certified HVAC professionals are qualified to properly size equipment.

Like any mechanical system, an HVAC system will require maintenance over time. For example, Refrigerant charge must be maintained at a specified pressure level. Over time, if there is a leak in the system, the pressure level will drop (even if Tom Brady isn’t playing). If not reset, your system may not function properly. The pressure levels need to be checked on some regular basis and adjusted as necessary. In addition, to ensure that the system operates efficiently, filters should be replaced on a regular basis. Consequently, homeowners are strongly encouraged to schedule semi-annual maintenance calls at which time a Technician will evaluate all of the components, change out the filters and make any necessary resets.

Because an HVAC system is comprised of multiple components, the changes of one or more component needing to be repaired or replaced over time is very high. The good news is that you can replace the component without having to replace the entire system. During the semi-annual maintenance visit, the Technician will evaluate whether any of your components are in need of repair and/or replacement.

With advances in technology, the efficiency of HVAC systems has increased substantially over the years. Thus, even if your existing system is functioning, you may be able to increase your comfort levels and decrease your monthly energy bills by upgrading to a newer system. Most importantly, you can do this without having to replace the existing ducts, substantially reducing the cost of installing a new system.