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How Heating & Air Conditioning Works

The more you understand about your HVAC system, the more confident you’ll be when talking with your local HVAC contractor about comfort option for your home.

This page will give you a top-level view of how a heating and air conditioning system works. We’ll only go into the details needed to give you a solid understanding.

There is a fundamental concept you must understand before proceeding: Indoor comfort is all about moving heat energy. In the summer season, an HVAC system moves heat energy out of your home. In the winter, it adds heat energy back into your air.

The above might sound basic, but you’ll see why it’s important as you continue reading. So get ready, you’re about to become a junior-HVAC pro!

How heating and air conditioning works - Find an HVAC Dealer

Air Conditioning

1) The thermostat signals air is too warm, and the air conditioner turns on and begins compressing refrigerant. Refrigerant, also known by terms like Puron™ and R-410A, starts out as a gas. When it is compressed, heat energy from the refrigerant is dissipated into the outside air, and the refrigerant condenses down into a chilled fluid.

2) The refrigerant is then pumped inside to the indoor coil, which is a serious of copper or aluminum piping. When using a furnace and air conditioner, the indoor coil is called an evaporator coil. When not using a furnace, the indoor coil is housed in an air handler (also called a fan coil).

3) Next the furnace fan motor begins pulling air from the home via the return air duct(s). The air is sucked through a filter and then forced up through the evaporator coil. The refrigerant absorbs heat energy and turns back into a gas. As heat energy is removed from the air, water condensates on the indoor coil, which also dehumidifiers the air to a certain degree.

How air conditioning works

Gas Furnace Heating

A natural gas or propane powered furnace is the most common type of heating installation in America. A furnace is also used during air conditioning, as mentioned above. That means the type of furnace fan motor you have will affect the noise level and efficiency of your summer cooling. But enough about that — on to heating!

1) A flame inside the furnace heats a metal grid called a heat exchanger. Modern furnaces boast fully modulating flames which means the flame can adjust by 1 percent increments (varies by manufacturer) to heat in the most efficient manner. After a few seconds, the heat exchanger is hot and ready to go.

2) The fan motor pulls air from the home via the return air duct. The air is filtered first before entering the system.

3) The air is forced through the heated heat exchanger, and then back into the home via ductwork.

*A variable speed fan motor can operate at different speeds to match heating needs and provide better comfort. Also, condensing furnaces capture heat energy in combustion gases that used to be wasted, making them more efficient.

How heating works

Using A Heat Pump

A heat pump looks identical to an air conditioner, and is all electric as well. In the summer, it compresses refrigerant for cooling your home just like an air conditioner does (see above). In the winter it reverses this process. Instead of dissipating heat energy into the outside air, and absorbing heat energy from the indoor air, it absorbs heat energy from the outside air and uses this to warm your indoor air.

When using a heat pump for heating, there is no furnace inside to contain the fan motor. For heat pump only installations, the furnace fan motor and the indoor coil in the evaporator coil are combined into what is called an air handler or fan coil.

Heat pumps can also be used with a furnace for hybrid heating. What does hybrid heating do? It switches off between the furnace and the heat pump based on outside temps. For rural areas where people are using propane to power their furnaces, a hybrid system can save a lot of money on winter time gas bills.

How a heat pump works

Ductless Air Conditioning and Heating

Another option for home comfort that you should ask your HVAC contractor about is a ductless mini-split system. The heating and air conditioning methods discussed above are called split-system designs because an air conditioner or heat pump sits outside, and the rest of the equipment is located inside the home.

However, sometimes an addition, office, garage or other living space doesn’t have ducting installed, or is not connected to the rest of the home’s ductwork system. In the past, noisy (and unsightly!) window and floor units were the only way to keep these area comfortable. However, ductless mini-splits make that a thing of the past.

A ductless mini-split system still uses the split system design, but the indoor air handler is very small, and easily mounted on a wall or recessing in a ceiling. A ductless air handler is designed to condition a single area, but you can run more than one indoor air handler off a single outdoor unit.

Ductless air conditioning and heating systems deliver high efficiency, quiet performance. Plus, ductless heat pumps from manufacturers like Mitsubishi can still heat even at sub-zero temperatures! If you haven’t asked your HVAC contractor about a ductless system, you’re missing out!

How Ductless Air Conditioning Works

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How Heating & Air Conditioning Works

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