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AC and Heating Tip from AC Express

How Do Heating Systems Work?

How Do Heating Systems Work?

In some ways, many of us take our air conditioning and heating in Austin for granted. We use our thermostats to control the very air around us like wizards without a thought about it. We expect warm air coming through the house in the winter and cool air in the summer. We use these wonderful devices to make our homes as comfortable as we want them to be when the outside world is anything but.

We know that our air conditioners and heaters work, but many of us don’t know how. In this tip, we’ll look at several of the different types and varieties of heaters and how the operate, what forces create the warm and what systems deliver it to the house and how. We’ll look at a number of varieties and distinctions between the different forms that furnaces, boilers, and heat pumps come in. This will be a primer on all things residential heating.

The Basics

Before we go over the specific ways each type of home heating system works, let’s go over the basic principles that fall behind the vast majority of types of heaters. A central heating system has a primary heating appliance such as a furnace or boiler located in an out-of-the-way place such as a basement or garage. It delivers heat throughout the house either by pumping warmed air through a system of air ducts or sending hot water or steam through pipes to room radiators or convectors.

There are a number of ways the heat gets produced and the distributed, and waste is disposed of, but all heat delivery systems have the same basic principles. There’s the primary unit, usually a furnace, boiler, or heat pump. It uses a fuel such oil, natural gas, propane, or electricity to produce heat, usually in the form of fire. That heat source then heats up a delivery substance, the thing that’s going to spread throughout the home, which is going to be either water or air. Then this heated water or air is distributed throughout the home either through ducts, pipes, or gravity. And that’s the general concept. There are many more details involved including what individual parts do to make this all happen and what each type of heater and their variations looks like in operation, but those are the concepts that surround the idea of central home heating systems. Next, let’s look at how furnaces work in particular.


We’ll start with how furnaces work because the vast majority of Americans use a furnace in their home to heat their household. A furnace fall under the category of a forced-air heating, because both furnaces and heat pumps distribute the hot air they create via the ductwork system in your house. This means that both the cool air in summer produced by your air conditioner and the warm air in the winter produced by your furnace operate through the same delivery system, despite the fact that these units are in fact separate.

The way the duct air delivery system works is quite simple. Air in these systems moves at about 700 feet per minute through the house in rectangular ducts, typically made from galvanized 30-gauge sheet steel. Some systems use round ducts connected to the main rectangular trunk, while other houses have flexible, round insulated ducts connected to an insulated trunk. In all cases, the joints in the duct system need to be meticulously sealed to prevent air leaks and energy loss.

For a gas based furnace, the cycle of heating works like this. First, the thermostat has a thermometer that reads that the temperature in the house is below the temperature that the thermostat is set to. If your thermostat is set to “on” and “heat”, it will then send a signal to the furnace to switch on. This low voltage transmission signals a valve to open in the furnace and deliver natural gas to the burners and for the blower to turn on. An electric igniter will ignite the fuel in the burner. This combusted hot gas begins to rise through the heat exchanger situated above the burner and heats the air. The blower fan then blows this heated air into the duct system. The air moves through the ducts, out the vents, and into the house. Once the thermostat reads that the temperature has reached its preset, it sends another signal to the furnace to switch off the fan and the burner.

Gas isn’t the only fuel source that can power a furnace though. But it is the most common. Oil is another furnace fuel. About 7 percent of U.S. homes heat with oil, collectively consuming about 7 billion gallons of fuel a year. Modern oil powered burners atomize the oil by pumping it at about 100 psi, or pressure per square inch, to a tiny brass or steel nozzle that turns it into a spinning, cone-shaped spray pattern consisting of about 55 billion droplets. The spray is ignited by a 20,000-volt arc produced by a pair of burner electrodes. This results in a clean-burning flame of 2200 to 2600 F. This flame heats the air in the heat exchanger, and then that air is delivered through the ductwork just like a gas furnace.


Not as many homes in the US have boilers as furnaces but they are still common enough to be worth talking and learning about. They are particularly more common in older homes and apartments. The primary difference between a boiler and a furnace is that a boiler works on the principle of water as the heat transport substance rather than air.

Boilers heat water which is transported through pipes to a radiator. That’s the basic idea of how most boilers work. Water is the ideal heat-transport vehicle. A small pipe filled with hot water carries as much heat as a large air-filled duct, meaning that in some ways boilers are more space efficient than furnaces. These pipes can fit far more easily between studs and joists. In most houses that use hot-water systems, the pipe carries water at 120 to 180 F to baseboard convectors that consist of a piece of copper tube running through a row of sheet metal fins. This sets up a convective heating loop as air is pulled in at the base and flows out the unit's top. Newer radiant-heat systems use plastic tubing routed in a serpentine pattern. Usually this is installed under wood-frame floors, or it is encased in concrete.

Parts of this heating cycle are much the same as the furnace. The thermostat reads that the temperature is below the temperature the thermostat has been set at. It sends a low voltage signal to the boiler which tells it to turn on. The boiler itself operates when the water temperature in the boiler drops below a threshold temperature, around 185° F. A temperature sensor in the boiler signals the boiler primary control which in turn ignites the burner. Gas fired boilers have a control valve to allow gas to flow into the burner. Those are the most common types of boilers. You also have oil boilers. Oil fired boilers have an oil pump which delivers oil at high pressure to an atomizing nozzle which sprays into the fire chamber. The fuel is ignited with a pilot light or electric igniter in much the same way as an oil-fueled furnace works.

There’s an air intake or burner blower that provides combustion air for the flame. There are safety devices involved that ensure that the boiler shuts off if there’s no fire to consume the fuel that’s let out. The boiler stops firing when the internal temperature sensor indicates the upper limit temperature for the water has been reached. The circulator stops the flow of water when the living area thermostat indicates the desired temperature has been reached.

Heat Pump

Heat pumps differ from furnaces and boilers in one primary aspect. They serve both as the heating and cooling system for a residential area. In many ways, heat pumps work very similarly to air conditioners. But the way they work is that in the summer they pull heat out of the house and send it outside and in the winter they pull heat from the outside and push it into the house. Either way, they work like furnaces in that they use a forced air system and move the air through the ductwork in your house.

Because when heating the heat pump has to take heat from the outside air, heat pumps only work at their most efficient when the temperature outside is above 30 to 35 degrees. Below that, it’s harder to extract heat from the cold air and a backup heater will be needed. For that reason, heat pumps are better suited to climates that don’t get extremely cold like Austin. Heating is achieved through refrigerant that absorbs the heat from the outside then transports it through to the house. One advantage of a heat pump is that it moves heat instead of generating heat, giving you more energy efficiency. Also, it is powered by electricity, so you can save substantially on fuel consumption.

The cycle of heating in a heat pump looks like this. First, just like all the other types, the thermostat recognizes that the ambient temperature in house has dropped below what the comfort level was set at. This triggers the thermostat to send a signal to the heat pump and both the air handler and the blower turn on. Refrigerant begins to cycle when the condenser in the outside unit powers on. The refrigerant starts to cycle through its system of copper tubing and coils. It warms up when outside by absorbing heat from the air around it, then it moves inside where it heats up the coils in the air handler in the indoor unit. These coils in turn heat up the air, which is sent into the ducts via the blower. The warmed air flows through the house until the thermostat reads that the right temperature has been reached in the house.

Heating Systems and Heating Repair in Austin

Regardless of whether you have a furnace, boiler, or heat pump, central heating is a remarkable feat of human engineering. There are many parts involved, from blowers and air handlers, burners and igniters, pipes and tubing, radiators and ducts and they all have to work together in perfect harmony to bring your house to that warm and comfortable state you’ve come to expect and love.

But because there’s so much involved in this process, things don’t always go the way they should. There’s no such thing as a perfect system and eventually parts wear out or get clogged. Leaks or cracks or debris can cause the heating system in your house to go on the fritz and when that happens it can be very frustrating. Fortunately, there are Austin heater repair companies such as AC Express to help you out in such instances. Heater repair in Austin is something you never want to need but you always want to be able to get at a moment’s notice. That’s why AC Express offers same day heater repair service. So if you find your Austin heating system isn’t quite doing its job the way it should, whether you’re in Hutto, Kyle, Leander or Liberty Hill, call AC Express!

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