Bringing in the Air
In order for a forced air system to work, air must be drawn in. This happens in a couple of different ways. Throughout any building are returns, or vents which draw air in to the ventilation system. Air conditioning systems work under the same premise, but draw in from outside. Due to their size and noise, air conditioning condensers are usually stationed outside, either on the roof or on the ground, adjacent to the building.
Heating the Air
The air is drawn through a filter and passed over heating elements, which increase the temperature of the air. Forced air heating systems utilize a gas -- propane, natural gas or heating oil -- which is incinerated to create the heat. A fan at the end of the heating venue, draws the air through the HVAC System and pushes it out through the building.
Cooling the Air
A large fan on the unit draws air into the condenser. A liquid coolant inside of the condenser is used to take air of any temperature and make it cold. The cooling agent is similar to that used in home refrigerators and freezers. The air is then drawn through the furnace filter and through the house by the main fan in the furnace.
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