The HVAC system is the mechanical plant in our customer’s home. Many different components work together in order to provide comfort in an efficient way. Technicians who wish to fulfill their customers’ needs should be aware of these various components. Today we will examine the equipment that makes up the mechanical plant and the signature features that combine to make it operate efficiently.

Furnace — The heart of the heating system. Furnaces today combine variable-speed motors, multi-stage heat output, and secondary heat exchangers for high-efficiency operation and increased humidity control potential. Sophisticated electronic circuit boards even come with self-diagnostic capabilities.

Condenser — The heart of the cooling system. Multi-stage compressor technology and improved heat transfer areas allow this piece of equipment to efficiently reject the heat built up from within the house.

Evaporator Coil — Located in line with the supply airside of the furnace, the evaporator coil absorbs heat from the house and transfers it via refrigerant lines to the condenser outside.

Heat Recovery Ventilator (HRV) — The HRV can operate as a stand-alone system or it can be tied into the ductwork of the existing system. The ventilator brings in fresh air from outdoors and exhausts stale indoor air. Advanced technology allows a minimum loss of heating or cooling during this process.

Humidifier — Located on either the supply or return air ductwork in a whole-house system, the humidifier provides moisture to the indoor environment. Automatic technology allows the humidifier to adjust to outdoor temperatures and provide the correct amount of humidity.

Air Cleaner — Available today in multimedia, electronic, and HEPA technology, the air cleaner is designed to trap pollen, animal dander, dust, and mold spores. In addition to helping improve the indoor air quality (IAQ), the air cleaner helps to keep the equipment clean.

Zoning — Thermostats control dampers located within the ductwork. The dampers will regulate airflow depending on the need for heating and cooling in the area where the thermostats are located.

Transitional and Telescoping Plenum — Adjustable ductwork that is fitted to the return and discharge sides of the furnace. It connects the furnace to the return and supply air systems.

Return Air Ductwork — The distribution of ductwork within the house that returns air back to the furnace for conditioning or air recirculation.

Supply Air Ductwork — The distribution of ductwork that supplies conditioned or recirculated air within the house.

UV Light — Located within the ductwork, the light uses ultraviolet (UV) technology to reduce and/or kill airborne contaminants inside the house.

Thermostat — Usually located within the living environment, the thermostat senses a need for heating and cooling and sends an electrical signal to initiate equipment operation. Advanced technology allows for remote communication via telephone or Internet with HVAC systems.

The system presented here is based around a forced-air furnace. High efficiencies can also be found in heat pumps and boilers.

The Web sites of major equipment manufacturers are a great place to visit for additional information. Check your brand-new edition of the The News HVACR Directory & Source Guide for Web site listings.

Rothacker is a member of the National Comfort Institute’s Advisory Board and a National Comfort Team Founding Member. For questions or comments on Tech Basics, contact Rothacker by e-mail at

Publication date: 01/20/2003