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In order to know exactly how big (or small) it should be, the contractor needs to calculate how much cooling and heating capacity it must have to keep the occupants comfortable. This is called the load of the home. The load of the home is partly dependant upon the home’s square footage. However, a true load calculation goes beyond that. An accurate load determination includes building construction; orientation to the sun; “R” value of the insulation; number, size, and placement of rooms; number, size, and placement of windows and doors; types of windows and doors (thermal efficiency); number and arrangement of floors; Residential load calculations make use of mathematical formulas that take all these variables into consideration. They have been computerized, so they’re not as time-consuming as they were in the past. Determining the load by using rules of thumb almost always leads to an over-sized heating and cooling system, resulting in an increased initial cost, increased monthly utility bills, increased maintenance, and shortened equipment life because the equipment cycles off and on too frequently.

Who Does the Load Calculation? The contractor you choose to install your new system should be able to perform these calculations. You may ask him for this service. If he doesn’t want to do it, or says it isn’t necessary, you may want to look for a different contractor. In some areas, the local utility will perform a load calculation – check with your local utility. How Big Is Big? Cooling size is given in tons of cooling; 1 ton = 12,000 Btu/h. 'SEER' (Seasonal Energy Efficiency Ratio) indicates the efficiency of the air conditioning unit, not its capacity. Why it’s Important to Have the Right Sized System Having the wrong-size heating-cooling system can lead to multiple problems. Over-sizing your cooling system is not a good thing. Without getting into too much detail, your cooling load consists of two parts: We’ve all heard the saying, “It’s not the heat; A cooling system that is too big cools down the temperature very quickly, but it does not run long enough to remove sufficient moisture or “humidity” from the air.

The result is you feel cool but clammy. tents made for ac unitsMany people then turn down the thermostat to make the air conditioner run longer, increasing the utility bill. heat pump ac unit not workingIn some cases, the insufficient moisture removal resulting from over-sized cooling equipment can lead to mold growth and other types of moisture-related damage.best 3 ton air conditioner unit A correctly sized cooling system runs long enough to “wring” moisture out of the air. This allows you to be comfortable at a slightly higher thermostat setting and allows you to save money on your utility bill. It also takes care of the “mugginess” without making you feel too cold. Air conditioning systems are sized in “tons,” which is a measure of the rate at which they deliver cooling, not how much they weigh.

One ton of cooling is equal to 12,000 Btu/h (British Thermal Units per hour), the rate of cooling required to freeze one ton of ice at 32°F in one day. It is better to have a system that supplies a little less than the required tonnage of cooling, rather than a system that supplies more than the required tonnage of cooling. Heating and Cooling Equipment Efficiency Ratings The table below shows efficiency ratings for good, better and much better heating and cooling equipment. SEER means Seasonal Energy Efficiency Ratio and provides an annual measure of the efficiency of the air conditioner. Higher numbers use less energy. AFUE means Annual Fuel Utilization Efficiency. HSPF means Heating Seasonal Performance Factor. For existing homes, the contractor should also check the condition of your ducts. Ducts deliver heated or cooled air to your rooms. Ducts that excessively leak air or that do not deliver the right amount of air to each room can increase operational cost from a few percent to over 50%.

Window Air Conditioner Operation A window air conditioner, also known as a window A/C or a room air conditioner, is designed to cool a single room and can be a good, easy-to-install option if a central air conditioning system is not practical or if you want to cool a single room rather than the whole house. Depending on the model, a window air conditioner can operate in different modes. The cooling mode takes in room air, cools it and directs it back into the room. Some models allow you to select from several preset cooling levels; the air conditioner cools at the selected level until you change the setting or turn the unit off. Other models let you set a desired temperature for the unit to maintain. The air conditioner operates until it senses that the air is at the desired temperature and then cycles off, cycling back on when the temperature rises above the specified setting. A fan-only mode uses less energy because it doesn't provide cooling. The appliance simply circulates and filters the room air.

Some window air conditioners have a heating mode. As with the cooling function, you set the desired temperature and the heating system cycles on and off to maintain it. CautionFollow the air conditioner manufacturer's instructions for safety, installation and operation. Choosing a Window Air Conditioner The right air conditioner helps you cool a room efficiently. An undersize unit won't cool adequately while one that's too large will not remove enough humidity, leaving the air feeling damp. To find the proper air conditioner, determine the square footage of the room you want to cool by multiplying the room length by its width. You also need to know the air conditioner's BTU (British Thermal Unit) rating, which indicates the amount of heat it can remove from a room. A higher number means more cooling power for a larger room. Compare your room size to the BTU rating: 150 to 350 sq ft: look for a 5,000- to 8,000-BTU unit 350 to 550 sq ft: look for an 8,000- to 12,000-BTU unit

550 to 1,050 sq ft: look for a 12,000- to 18,500-BTU unit 1,050 to 1,600 sq ft: look for an 18,500- to 25,000-BTU unit Consider conditions that may reduce the cooling need — the room is always shaded, for example — and those that may increase it — the room receives a lot of direct sunlight or regularly has more than a couple of occupants. Keep in mind that as the BTU rating increases, the size and weight of the air conditioner does as well. Good to KnowEER stands for Energy Efficiency Ratio. A higher EER indicates a more efficient air conditioner. Window Air Conditioner Considerations Most window air conditioners are designed to fit double-hung windows, which have a sash you can raise or lower. Measure the inside dimensions of the installation window carefully to make sure you find a model that fits. Don't rely on estimates. Here are some other things to think about: Window air conditioners are heavy. Enlist a helper when carrying and installing the unit.

Installing the air conditioner in a shaded window will help it operate more efficiently. A window facing north will be in shade most of the day The window you select for installation needs a suitable power outlet nearby. The manufacturer may specify that you plug the device directly into the outlet with no extension cord. The circuit the outlet is on must be able handle the electrical load of the air conditioner. Different models have different plug configurations. Make sure the air conditioner you select is compatible with your outlet. Check the product packaging for the plug design. CautionNever alter an electrical plug. Contact a licensed electrician if you have any doubts or questions about the circuit or outlet or if work such as installation of a new circuit or plug is necessary. Window Air Conditioner Features A programmable timer lets you set the unit to turn on and off at specific times, helping you reduce energy consumption by operating the air conditioner only when it's needed.

Mechanical controls allow you to adjust fan speed and cooling level and are simple to operate. Electronic controls give you more flexibility, allowing you to set a specific temperature for the air conditioner to maintain. A sleep setting increases the specified temperature incrementally over a period of time before returning to the original setting several hours later. This feature keeps the air conditioner from maintaining an unnecessarily cool temperature in a room where the occupants are sleeping. It also reduces noise since the unit is running less frequently. An electronic ionizer helps the air conditioner more effectively remove impurities such as pollen from the air. Venting options let you choose between recirculating room air, pulling outside air into the room and exhausting room air to the outside. Air conditioners remove humidity from the air as they cool it. Different models have different dehumidification capabilities. Look for a rating measured in pints and ounces of moisture removed per hour.

A remote control adds convenience — you can adjust settings and turn the air conditioner on and off from across the room. Some remotes can function as temperature sensors, activating the air conditioner when the air around the remote is warmer than the temperature specified in the settings. A filter alert lets you know when the air filter needs cleaning. An extra-long cord helps you reach a power outlet. Window Air Conditioner Operating Tips There are several things you can do to help a window air conditioner cool your home: Make sure the air can flow freely around the air conditioner. Outside of the home, keep the unit clear of obstructions such as shrubbery. Inside, make sure obstructions such as window treatments and furniture are clear of the unit. Help keep the cool air in the room by closing fireplace dampers and floor or wall registers. Reopen them when using the fireplace or home heating or cooling system. Consider closing window treatments when it's sunny outside, but remember to avoid blocking the air flow around the air conditioner.

Keeping the exterior of the room you're cooling shaded will help the air conditioner keep you cool, but make sure that airflow around the exterior of the unit is not restricted by trees, shrubs or other obstructions. Maintain correct insulation and weatherstripping throughout your home. See Install Insulation to learn about insulating your home. Read Weather Strip Your Doors and Weather Strip Your Windows to learn about sealing air leaks in your home. When possible, reduce the workload of the air conditioner by using appliances such as dishwashers, ranges and dryers during the cool hours of the day. Use accessories such as weatherstripping and foam side panels to help you seal and insulate the area around the air conditioner. Window Air Conditioner Maintenance Simple maintenance helps keep an air conditioner operating efficiently and can maximize its lifespan. Unplug the air conditioner before performing maintenance. Here are some common procedures: Check and clean the air filter regularly as specified by the manufacturer.