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Heating Systems

Explores the different methods of conducting thermal energy though our homes to keep us comfortable.

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Heating Systems

A roaring blaze in a fireplace is a good way to keep toes toasty on a cold winter day. But you probably wouldn’t use a fireplace to heat an entire house. Do you know how your home is heated?

Heating the Home

Modern home heating systems keep us comfortable in cold weather. We may even depend on them for our survival. But we often take them for granted. Two common types of home heating systems are hot-water and warm-air heating systems. Both types are described below. You can watch an animation showing how a solar heating system works at the following URL.


Thermal energy is the total energy of moving particles of matter. The transfer of thermal energy is called heat. Therefore, a heating system is a system for the transfer of thermal energy. Regardless of the type of heating system in a home, the basic function is the same: to produce thermal energy and transfer it to air throughout the house.

Hot-Water Heating System

A hot-water heating system produces thermal energy to heat water and then pumps the hot water throughout the building in a system of pipes and radiators. You can see a simple diagram of this type of heating system in the Figure below.

  • Water is heated in a boiler that burns a fuel such as natural gas or heating oil. The boiler converts the chemical energy stored in the fuel to thermal energy.
  • The heated water is pumped from the boiler through pipes and radiators throughout the house. There is usually a radiator in each room. The radiators get warm when the hot water flows through them.
  • The warm radiators radiate thermal energy to the air around them. The warm air then circulates throughout the rooms in convection currents.
  • The hot water cools as it flows through the system and transfers its thermal energy. When it finally returns to the boiler, it is heated again and the cycle repeats.

Schematic of a warm water heating system

Q: Look closely at the hot-water heating system in the Figure above. The radiator is a coiled pipe through which hot water flows. What happens to the water as it flows through the radiator? Why is each radiator connected to two pipes? Why can’t water flow directly from one radiator to another through a single pipe?

A: The radiator is where most of the energy transfer occurs. Water passes through such a great length of pipe in the radiator that it transfers a lot of thermal energy to the radiator. As the water transfers thermal energy, it gets cooler. The cool water flows into a return pipe rather than going directly to another radiator because the cool water no longer has enough thermal energy to heat a room.

Warm-Air Heating System

A warm-air heating system uses thermal energy to heat air and then forces the warm air through a system of ducts and registers. You can see a this type of heating system in the Figure below.

  • The air is heated in a furnace that burns fuel such as natural gas, propane, or heating oil.
  • After the air gets warm, a fan blows it through the ducts and out through the registers that are located in each room.
  • Warm air blowing out of a register moves across the room, pushing cold air out of the way.
  • The cold air enters a return register across the room and returns to the furnace with the help of another fan.
  • In the furnace, the cold air is heated, and the cycle repeats.

Warm air heating system

Warm-air heating system.

Q: How does a home heating system “know” when to run and when to stop running?

A: A home heating system is turned on or off by a thermostat.

How a Thermostat Works

A thermostat, like the one seen in the Figure below, is an important part of any home heating system. It is like the “brain” of the entire system. It constantly monitors the temperature in the home and “tells” the boiler or furnace when to turn on or off. The thermostat is set at a selected temperature, say 71 °F. When the temperature in the home starts to fall below this point, the thermostat triggers the boiler or furnace to start running. When the temperature starts to rise above this point, the thermostat triggers the boiler or furnace to stop running. In this way, the thermostat maintains the home’s temperature at the set point.

Thermostats help regulate temperature


  • Types of home heating systems include hot-water, warm-air, and solar heating systems. All of them have the same basic function: producing thermal energy and transferring it to air throughout the house.
  • A hot-water heating system burns fuel in a boiler to produce thermal energy. The thermal energy is used to heat water, which is pumped through a system of pipes and radiators.
  • A warm-air heating system burns fuel in a furnace to produce thermal energy. The thermal energy is used to heat air, which is forced through a system of ducts and registers.
  • A thermostat controls a home heating system. It monitors the home’s temperature and triggers the boiler or furnace to turn on or off to keep the temperature at a set point.

Explore More

At the following URL, read how a gas furnace works. Then fill in the blanks in the statements below. http:///www.fourseasons-chicago.com/news/how-a-furnace-works/

  1. The __________ pulls air through the unit to start combustion.
  2. The component where gas undergoes combustion is the __________.
  3. The __________ opens to allow gas to flow through the burner.
  4. The gas is ignited by an igniter or a(n) __________.
  5. The __________blows air over the heat exchanger.
  6. The component where air is heated is the __________.


  1. What is the basic function of any home heating system?
  2. Create a table comparing and contrasting hot-water and forced-air heating systems.
  3. Try to identify the type of heating system (if any) where you live.



Part of a heating system that monitors temperature and controls when the boiler or furnace turns on or off to keep the temperature at a set point.

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