How Does My Heating System Work? (Part 1)

So, you have a heating system in your home. And it probably works fine, most of the time. But do you really know what it is doing? Or how it is doing it? Does it matter? Yes it does! Understanding how your heating system works will help you in two ways: 1) You will understand why regular maintenance is a necessity, not just a luxury; and 2) You will know how to get the most out of every penny you spend in energy costs.

The Basics 

First let’s go over some basics. Every heating system must have a thermostat. The thermostat is how you tell your heating system when and how long to run by setting the temperature that you want in your house. Let’s say you want it to be 70 degrees inside. When the thermostat feels the air temperature dropping below 70, it turns on the heating unit. The heating unit converts the fuel it is using (electric, gas, oil, etc.) into heat and distributes it throughout your home. Then as the thermostat feels the air warming above 70 degrees it turns off the heating unit. Simple thermostats allow the temperature to go up or down a few degrees from your set temperature so that your heating unit isn’t turning on and off a lot. More advanced thermostats can calculate how often your heating unit needs to run in order to keep the temperature steady without the up and down temperature swing.

How about the heating unit? We will explain the two most common types: Heat Pumps and Hot Air Furnaces.

Heat Pumps – How do they work? 

For many people Heat Pumps are mysterious.  But in reality they are not that complicated. A heating system that uses a Heat Pump has the following two parts: A Circulating Fan-Coil unit or ‘indoor unit’, and a Compressor/Condensing unit, or ‘outdoor unit’. (In most cases the Circulating Fan-Coil unit is inside your house. However if you have a ‘packaged unit’ then both parts are built together and are outside. For simplicity we will call them the ‘indoor unit’ and the ‘outdoor unit’.)

Electricity is the fuel for a Heat Pump, but the electricity is not being directly converted into heat. Instead the electricity powers a process that uses refrigerant to transfer heat from outside to inside your home. “But wait!”, you say, “How can the air outside on a cold winter day heat up my home?” Easy! Let me explain. 

The ‘outdoor unit’ is the heart of your heating system. When the thermostat tells it to come on, then the compressor, which is like a pump, pushes hot refrigerant into the ‘indoor unit’. The hot refrigerant heats up the coil, which looks something like a car radiator. The fan in the unit pulls air from your house through a filter, and then through the coil. The hot coil heats up the air which is then blown into your house.

The refrigerant leaving the coil of the ‘indoor unit’ is now cooler and goes out to where the compressor is. Then it is pumped through a tiny nozzle as a mist into another coil outside. This mist is very, very cold which means that even on a winter day there is enough heat in the air outside to heat up this mist. Now the refrigerant is a cool vapor so the compressor heats it and pumps it into the ‘indoor unit’. And the cycle continues.

There’s just one more helpful detail to explain. If the temperature outside is below freezing, then the coil outside will gradually build up with a coating of frost. This is normal. However the ‘outdoor unit’ will go into a defrost cycle every hour or two so the frost doesn’t keep building up. During the defrost cycle, the coil of the ‘indoor unit’ gets cold for several minutes. But to keep the house from cooling down, the ‘indoor unit’ also has electric heating elements. These are similar to what you see in your toaster, just much more powerful. During the several minutes of the defrost cycle these turn on so you don’t feel cold air blowing into your home. These also act as a back-up or auxiliary heat source by turning on if the temperature in your home falls 3 or 4 degrees below your set temperature.

See? That wasn’t so hard! Now, what about the biggest question: How does this help me? Are you ready to see how this will help you care for your system, and how to get the most benefit out of what you pay for energy? And what about Hot Air Furnaces? We’re going to cover those questions next. So stay tuned for Part 2! (Update: You can now read Part 2 here!)

Do you have a question about any of this? Visit our “Ask an Expert” page and ask away!

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