Heating systems come in all sizes, types and fuels. You can check out a brief history of heating. In residential systems there are basically two different distribution systems, forced air (ductwork) and radiation (baseboards). These systems can be fueled by one or more of electricity, natural gas, LP propane, oil, hot water, steam, geothermal, heat pump or wood.
For most purposes you can categorize home heating systems into two broad categories, furnaces and boilers. Generally speaking furnaces heat air and use a system of fans and ductwork to move that air around the house. Boilers heat water and use a circulator pump and piping to move the water through radiators, thus heating the home.
Furnaces come in all shapes, sizes, efficiencies and fuels. The most common furnace in urban areas is a forced air, natural gas unit. In rural areas, or areas that do not have access to natural gas pipelines, furnaces often use propane or electricity to produce heat. Regardless of the fuel all residential furnaces work on the same principle. A fuel is burnt in a heat exchanger to produce heat. Air is then passed over the heat exchanger where it picks up heat, the air is then delivered to the house through a ductwork system.

YES! Your heating system is a finely tuned piece of machinery that is designed to squeeze the most heat from your energy dollars. Your heating system operates for months on end and if one of the components of that system is not working in harmony with the rest of the furnace, you are losing efficiency and money.
Annual maintenance inspections often spot small problems before they become large, and very expensive repairs.

DISPOSABLE FILTERS - Disposable filters should be changed every 6 to 8 weeks. A lot of people try cleaning these filters but they are not really meant to be cleaned and may actually become even less efficient. Disposable filters are not very efficient and provide only a basic amount of air cleaning. If you run your furnace fan continuously, cleaning should be performed every 3 to 4 weeks.

WASHABLE FILTERS - Washable filters should be cleaned every 6 to 8 weeks for normal use. If you run your furnace fan continuously, wash filters every 3 to 4 weeks. When you wash your filter be sure to inspect it for wear and tear.

HAMMOCK - Hammock filters are not meant to be washed and should be replaced every 8 to 10 weeks. When you purchase a replacement hammock filter it may be a little larger than the metal frame it’s attached to. Install the filter on the frame and then trim off the excess.

ELECTROSTATIC AIR CLEANER - Electrostatic air cleaners must be cleaned monthly. To clean them first vacuum the nylon media and then rinse the filter with water. Be sure to rise the filter in the opposite direction from the air flow. Electrostatic air cleaners are very difficult to get very clean so as your filter gets older, clean it even more often. When cleaning inspect it for damage and wear and tear.

ELECTRONIC AIR CLEANER (EAC) - The most important thing to remember about electronic air cleaners is to keep them clean. EACs are very efficient until the cells get dirty and then lose a lot of their efficiency. When cleaning the cells be careful not to break any of the thin wires that run along the outside of the cells. If one of these wires break, the cell current will be broken and will not work. Do not forget to clean the small prescreens as well.

CENTRAL Air Conditioners: - Central air conditioning units will cool a large area by using an air distribution system. The most common application is to add a central air conditioning unit to an existing forced air furnace. The air conditioner unit (condenser) is placed outside and is connected to the evaporator coil, inside the furnace's ductwork.
VARIATIONS: - Attic installations. In some warmer areas central air units may be installed with their own ductwork. In these cases a blower coil is used to circulate air through the ductwork. The ductwork can be installed in the basement or attic.

Anything is possible, but if you do not have a centralized air distribution system, or ductwork, in your home, installing air conditioning may be difficult.
If your home is a bungalow and the basement is not finished, then the situation is not so bad. Ductwork and a new furnace or blower coil can be installed in the basement and your new air conditioner installed outside.
If your home is two story, or the basement is completely finished, it becomes more difficult. Ductwork can still be installed in a finished basement, but you will probably have to tear down some walls and ceilings, and have to build bulkheads to hide the new ductwork.

NO!
There is sometimes a tendency to believe that BIGGER is BETTER. Sometimes that maybe so, but not in air conditioning units. Actually with central air conditioners, SMALLER is SMARTER. The first thing an air conditioner has to do to cool your home is to remove humidity from your home. If the air conditioner is too large, the air is super cooled before the humidity is removed. This will make you feel cool and clammy, much like a rainy fall day.

The most important thing to look for when purchasing a central air conditioner has nothing to do with the actual air conditioner and everything to do with the contractor you choose.
The best piece of equipment, if installed incorrectly, will not give you the comfort you deserve.

Turn your air conditioner OFF.
Call your service contractor immediately.

This will depend on the type and make of your central air conditioner, however all central air units require some clearance from trees and shrubs to allow for air flow around the condensing coil. Generally speaking you should try and keep any items that may interfere with air flow at least 30" from your unit.