Any forced air system in your home - whether it is powered through electric or gas-generated energy - requires a blower motor. This component consists of an electric motor and fan, and is responsible for pushing air evenly through the furnace. As points out, you can easily identify the blower motor in your furnace as the part that looks similar to a hamster wheel at the bottom of the unit. If it stops working, the air needed to heat your home will no longer be pushed through the furnace to be heated and distributed evenly. In that case, you need to inquire about potential repairs. Blower motor repair typically costs between $150 for a simple fix, and $450 for complete replacement and installation of the part. Where you land on that range depends on the exact damage.
Your HVAC professional can also help you verify that your system is properly matched by providing you with an AHRI Certificate of Certified Product Performance upon request. The certificate verifies that the outdoor unit (condenser) and the indoor unit (evaporator) combination has been certified as a matched system by the Air Conditioning, Heating and Refrigeration Institute (AHRI). For higher efficiency systems, this certification may help you obtain a rebate from your utility or local municipality if you have to replace your unit in whole or in part. Not all areas offer a rebate, but your technician will likely be able to provide information about the certification process. Fees for performing this certification vary, but generally are relatively inexpensive.
If your air conditioning is blowing warm air—or not working at all—it's time to call in the experts. After all, we're not just talking about an uncomfortable afternoon on a hot day: we're talking about your happiness at home, and a problem that may cause extensive damage to your system if not addressed quickly. That's why it's smart to catch problems early before they become expensive to address.

Absorption refrigerator Air barrier Air conditioning Antifreeze Automobile air conditioning Autonomous building Building insulation materials Central heating Central solar heating Chilled beam Chilled water Constant air volume (CAV) Coolant Dedicated outdoor air system (DOAS) Deep water source cooling Demand-controlled ventilation (DCV) Displacement ventilation District cooling District heating Electric heating Energy recovery ventilation (ERV) Firestop Forced-air Forced-air gas Free cooling Heat recovery ventilation (HRV) Hybrid heat Hydronics HVAC Ice storage air conditioning Kitchen ventilation Mixed-mode ventilation Microgeneration Natural ventilation Passive cooling Passive house Radiant heating and cooling system Radiant cooling Radiant heating Radon mitigation Refrigeration Renewable heat Room air distribution Solar air heat Solar combisystem Solar cooling Solar heating Thermal insulation Underfloor air distribution Underfloor heating Vapor barrier Vapor-compression refrigeration (VCRS) Variable air volume (VAV) Variable refrigerant flow (VRF) Ventilation
Energy efficiency can be improved even more in central heating systems by introducing zoned heating. This allows a more granular application of heat, similar to non-central heating systems. Zones are controlled by multiple thermostats. In water heating systems the thermostats control zone valves, and in forced air systems they control zone dampers inside the vents which selectively block the flow of air. In this case, the control system is very critical to maintaining a proper temperature.
In 1758, Benjamin Franklin and John Hadley, a chemistry professor at Cambridge University, conducted an experiment to explore the principle of evaporation as a means to rapidly cool an object. Franklin and Hadley confirmed that evaporation of highly volatile liquids (such as alcohol and ether) could be used to drive down the temperature of an object past the freezing point of water. They conducted their experiment with the bulb of a mercury thermometer as their object and with a bellows used to speed up the evaporation. They lowered the temperature of the thermometer bulb down to −14 °C (7 °F) while the ambient temperature was 18 °C (64 °F). Franklin noted that, soon after they passed the freezing point of water 0 °C (32 °F), a thin film of ice formed on the surface of the thermometer's bulb and that the ice mass was about 6 mm (1⁄4 in) thick when they stopped the experiment upon reaching −14 °C (7 °F). Franklin concluded: "From this experiment one may see the possibility of freezing a man to death on a warm summer's day."[9]