HVAC system parts: what each component does
Know the names of the main parts and a service call gets easier to follow. Here is what each one does and which ones you can safely look at.
What are the main parts of an HVAC system?
A home system has five jobs: ask for heat or cooling, make it, move it, distribute it and exhaust what is left. Each job belongs to a few parts. The thermostat asks. The furnace, heat pump or air conditioner makes. The blower moves. The ducts distribute. The vent or flue exhausts.
Learn those five and most service conversations make sense.
The parts, grouped by job
| Job | Part | What it does |
|---|---|---|
| Control | Thermostat | Reads room temperature and calls for heating or cooling |
| Heating | Furnace burners and heat exchanger | Burn fuel and pass the heat to the air without mixing the two |
| Cooling | Evaporator coil, condenser coil and compressor | Move heat out of the house through the refrigerant loop |
| Air movement | Blower and motor | Push air through the filter, the equipment and the ducts |
| Distribution | Ducts, registers and returns | Carry air to rooms and bring it back |
| Cleaning | Filter | Catches dust before it reaches the blower and coil |
| Drainage | Condensate line and pan | Carry away the water the cooling coil pulls from the air |
Which parts live where?
In a split system, the indoor half sits in a closet, basement or attic. It holds the furnace or air handler, the evaporator coil, the blower and the filter. The outdoor half holds the compressor, the condenser coil and a fan.
A packaged unit puts everything in one cabinet outside. The parts are the same. Only the location changes.
Why the refrigerant loop deserves respect
The compressor, the two coils and the refrigerant lines form a sealed loop. You never need to open it for routine care. Handling refrigerant takes federal EPA Section 608 certification, and doing it without that is illegal. If a part in this loop seems to be failing, call a licensed technician.
What can you safely check yourself?
Three things are fair game. Look at the filter and swap it if it is dirty. Keep the outdoor unit clear of leaves and weeds. Make sure supply registers and return grilles are not blocked by furniture.
Everything else is for a professional. That includes the burners, anything electrical and the start and run components inside the cabinets. Some of those parts can hold a dangerous charge even when the power is off.
If you ever smell gas or a carbon monoxide detector goes off, leave the house and call the gas company or 911. Do not go looking for the source.
Which part usually fails first?
Moving parts and electrical parts wear out before sealed or passive ones. Blower motors and contactors are common culprits. Ducts and coils tend to last longer, though they can leak or clog. A clean filter and an annual tune-up slow all of it down.
This article does not quote prices, rebates or tax credits. They change and vary by state and utility, so ask a local licensed contractor.
Frequently asked questions
What are the main components of an HVAC system?
A thermostat, a heating source such as a furnace or heat pump, a cooling source such as an air conditioner, a blower, ducts with registers and returns, and a filter.
What is the heart of an HVAC system?
For cooling, it is the compressor, which circulates refrigerant. For heating with gas, it is the heat exchanger. The blower moves the air in both cases.
Can I replace HVAC parts myself?
Filters, yes. Parts that involve refrigerant, gas or electrical work need a licensed technician. Refrigerant handling requires EPA Section 608 certification.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- ENERGY STAR. Energy Savings at Home: Heating & Cooling
- US EPA. Section 608 of the Clean Air Act