HVAC Replacement Basics

HVAC System Components

This article will help you understand the major components that make up an HVAC system and what they’re for. Whether you’re repairing your replacing your HVAC system, the more you understand about it, the better you can be at making good decisions for your home.

There are several major configurations of HVAC systems. The package unit, the split system, and the ductless mini-split. You can read more about these configurations in this article, but in short a package unit combines all parts of the system except the ductwork and thermostat in one package. Normally this is installed outside the home and is just connected by ductwork. A split system, “splits” the condensing unit from the evaporator/furnace and blower which is often located in the attic or crawlspace.

Next there are several different ways that heat can be delivered (A/C is always delivered the same basic way). This article is really localized to the mid-south, so we do not account for boilers and other common heating systems in colder parts of the country. Heat can be delivered as an air-source heat pump, a geothermal heat pump, and a gas furnace (either liquid propane or natural gas). Heat pumps are always paired with a second stage heat source since it becomes inefficient at lower temperatures, this is most often electric strips. You can read more about heat pumps here.

All that being said, a “system” by definition is made up of components that all work together (to achieve some purpose). When an HVAC system is designed for your home, it combines the following main components. 

  • Condensing Unit
  • Cased Evaporator Coil
  • Fan Coil (evaporator + fan)
  • Furnace/Air-Handler
  • Heat Strips

So a packaged heat pump, for instance, would have all of the following components in one box. Blower/fan, condensing unit, evaporator, and heat strips. A split A/C and furnace would have a condensing unit outside and the furnace, air-handler, and  evaporator coil in a separate unit in the crawlspace or attic. If you aren’t following the concept of split and package systems, read this and this. 

Within each of those components are the major parts that make them work. Below is a listing of the major components and the parts that make them up. For a definition of the parts and other HVAC terms see our HVAC parts glossary.

  • Condensing Unit
    • Compressor
    • Condenser Coil
    • Condenser Fan
    • Reversing valve (heat pump only)
    • Defrost Control (heat pump only)
    • Service Valves (Shrader Valves)
  • Cased Coil (Evaporator Coil)
    • Evaporator Coil
    • Expansion Device (TXV or Fixed Orifice)
  • Fan Coil (Evaporator Coil for Heat Pump)
    • Blower/Fan
    • Control Board
    • Heat Strips
    • Evaporator
    • Thermal Expansion Valve (TXV)
  • Furnace / Air-Handler
    • Control Board
    • Gas Valve
    • Heat Exchanger
    • Ignitor
    • Flame Sensor
    • High Limit Sensor
    • Rollout Sensor
    • Blower/Fan