The Mechanical System of a Home

Plumber looking at pipes

The main purpose of a home's mechanical system1) is to provide a comfortable and functional living environment. This "comfort system" actually contains three individual systems: heating, ventilation, and air conditioning; plumbing; and electrical.

Heating, Ventilation, and Air-Conditioning (HVAC)

The heating, ventilation, and air-conditioning2) components work together to provide thermal comfort and good indoor air quality.

Central Heating

Most homes, particularly in colder areas, have central heating. This type of system has a boiler, furnace, or heat pump that heats air, steam, or water in a central location like a furnace or boiler room. Ductwork or piping is installed throughout the home to distribute the heat.

How It Works
Furnaces3) are one of the most commonly used heat appliances. They have four main components:

  • Burners that deliver fuel like gas or oil (hybrid systems use both types of fuel)
  • A blower that moves the heat through the ductwork
  • A heat exchanger4) that transfers heat from the furnace to the home
  • A flue that exhausts gaseous by-products

The burners heat the air located along the outside of the heat exchanger. The blower5) carries this air out of the heat exchanger into the ductwork where it is distributed throughout the home. During warm weather, the heating system works with the central air conditioning system to cool the home. Air is cooled as it blows over the air conditioner's cooling coil, which is often attached to the furnace's air circulating fan. It is sent through the duct system into the home.

Air conditioning unitCentral Cooling

Central air conditioning removes heat from the home. In addition to cooling the home, an air conditioning unit can provide humidity control and ventilation. The split system is the most common type of central cooling system. It includes the following elements:

  • An outdoor cabinet that contains a compressor and condenser coil
  • An indoor evaporator coil that is generally installed in conjunction with the air handler or furnace
  • Compressor pumps that carry refrigerant through the system

How It Works
When the air inside the home blows across the evaporator coil, its heat is transferred to the refrigerant located inside the coil. This cools the air. The refrigerant is then pumped back into the compressor where this cycle begins again.

The heat that the refrigerant absorbed is carried outside the home and the cooled air is blown through the duct system into the home. The system also condenses the moisture in the air to decrease humidity.

The cooling system is generally combined with the central heating system because they share the same duct system.


Black fanVentilation is the process of removing airborne bacteria, dust, heat, moisture, odors, and smoke from a home. It involves (a) exchanging6) the air in a space with outside air to improve air quality and (b) circulating air within the house. There are two types of ventilation:

  • Natural ventilation occurs without the use of fans and other mechanical system devices. Air flows through cracks, small holes, walls, and windows7) as well as the roof (particularly if the home is not well-insulated).
  • Mechanical system ventilation uses fans and ducts to circulate fresh air.

Indoor Air Quality Equipment

HVAC systems can include devices8) that further improve indoor air quality. They remove allergens, chemicals, odors, and other irritants from the air. They can also manage the moisture level in rooms. Air cleaners, air purifiers, dehumidifiers, filtration systems, and humidifiers are common components of indoor air quality systems.


Sink faucet and water drippingThe plumbing system9) contains three main elements: a water supply system, a drainage system, and an appliance/fixture assemblage.

Plumbing Fixtures

A plumbing fixture10) is any device that connects to a" plumbing system and interacts with water." The most common fixtures are bathtubs, faucets, showers, sinks, toilets, and tubs. Drains, pipes, and valves bring water to each fixture and remove it as well.

Water Supply System

Tightening water pipesThe water supply system distributes water throughout the house. It consists of a water supply line11) that connects to the home's main line, which connects to the municipal water system. This line is located below the frost line so it will not freeze. It enters the house and then splits into two lines. One supplies cold water, and the other one connects to a water heater that provides hot water.

Some homes have water supply manifold systems, which contain large panels with blue valves on one side and red ones on the other. Each valve controls a hot or cold tube that provides water for a fixture. This system makes it easier to turn off the water supply to one fixture without turning it off to other areas of the home.

Drainage System

Drainage pipes remove unwanted water from the home to the septic or sewage system. They are connected to fixtures via drains that release water into the pipes. Every drain has a trap, which is a pipe that curves down and then back up. A small amount of water is retained in the curve. This water creates a barrier that prevents sewer gases from entering the home.

Most drains are vented to prevent negative air pressure from drying out the trap and keep positive air pressure in the sewer from pushing gases past the water barrier. This ventilation system also prevents water locks that can form in drain pipes and cause clogs.


The electrical system12) is carefully designed to safely deliver the power that home owners need for modern living. It generally works in the following manner:

Electricity is delivered to the home via aerial transmission lines.

  • Power enters the home through a meter, which records the amount of electricity that the home's occupants use.
  • The circuit breaker panel located in the home divides the power into separate circuits. (An electric circuit13) is a "path for transmitting electric current." It consists of a device that supplies the energy, a device that uses the energy, and transmission lines or wires that connect the two.)

The Meter

The main line usually runs from a pole (or sometimes from underground) to the house where it connects to the meter. Meters are usually installed outside of the home so meter readers can more easily get to them.

Most meters have a spinning wheel and mechanical numbers. Some newer models, however, are digital so they have LCD screens. Meters use kilowatt hours (kWh) to keep track of the amount of electricity used in a home. The increase in the number of kWh from one month to the next is used to calculate electric bills. provides extensive information about residential real estate including home construction and design.

Man checking electric metersThe Main Breaker Panel

A main breaker panel is generally installed inside the home, although it might be possible to install a weather-proof panel outside of it. The main electric supply line leaves the meter, enters the home, and arrives at "the main breaker panel at the main circuit breaker."

The main breaker determines the maximum amount of electricity that occupants of a home can use at one time. It switches off when the home experiences of an overload, which reduces the risk of electrocution and fire. Most modern homes have 200 amperages (amps) of service. Older homes may only have a 100 amp service, and a larger home may have a 400 amp service. The total amperage for a house is printed on the largest breaker switch on the main breaker panel.

Smaller circuit breakers that control the amount of electricity available for each circuit are located below the main breaker. These circuits generally pertain to individual rooms, but they may represent appliances like water heaters, furnaces, or air conditioners.

Copper wiresCircuits

Bundles of copper wires run—from smaller circuit breakers—through ceilings, floors, and walls to each room as well as hard-wired appliances. Each bundle of wires contains at least three wires. One of these wires is bare and two of them have plastic insulation.

The black and/or red insulated wires (known as hot wires) run directly from the circuit breakers. The white insulated (or neutral) wire carries the current back to the panel. The bare (or ground) wire is the "safety" element of the circuit.

The insulated wires attach to outlets or switches. When nothing is plugged in an outlet or a switch is off, the wires do not meet. When something is plugged into an outlet or a switch is turned on, the circuit is completed. This allows electricity to flow through an appliance or a light to activate it.

WiresThe ground wire runs to the ground, which works with the circuit breaker when a short circuit occurs. The network of bare copper wires that connect to every metal electrical box and every device in a home forms the grounding. These wires end in a grounding bar14) situated in the main service panel. This bar connects to a grounding rod located deep in the ground outside the house. If a break in the wiring system causes electricity to spill out of the black/red and white circuit wiring, the grounding system "provides a path of least resistance" for it to take back into the ground. The circuit breaker is triggered to shut off, which helps to prevent fire or electrocution.

The round slot on each outlet receptacle in a home is part of the grounding connection. When a grounded appliance is plugged into an outlet receptacle, its grounding prong directly connects to the network of bare copper grounding wires inside the circuits.

The mechanical system helps to ensure that a house provides the comfort and functionality that its occupants need. The HVAC system provides heating, ventilation, and cooling. Equipment like air purifiers and filtration systems that improve indoor air quality can be incorporated into these systems. The plumbing system ensures that water flows to and from the home and prevents toxic sewer gases from entering the home. The electrical system powers the home.

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