How a Furnace Works Made Simple

Your furnace is an integral part of your home, but it often goes without much attention or thought. However, without the right attention at the right time, you may be left with a cold house. Let’s get to the fundamentals of what makes your furnace work, what poses risks to your family, and what attention you should give it as it serves your home.

Types of Furnaces

When it comes to furnaces, you have two distinctly different types. In moderate climates, like southern California, you may see electric furnaces. These use an electric resistance element to generate the heat needed to warm your house. They are simple, generally safe, and do not rely on any type of fuel to operate. Plus, they are more efficient, with some models reaching a 100% AFUE rating. However, they are still more expensive to run, being electricity is more expensive than furnace fuels.

The most common type of furnace used in residences around the United States are fuel-burning systems. There are a variety of options for fuel used, including natural gas, propane, and oil. In more heavily developed areas, natural gas tends to be the fuel of choice, being it’s delivered to the house through underground lines. New gas systems have an efficiency rating of anywhere between 80% and 98%, depending on the unit. They generate more heat at one time, so they tend to heat your home more quickly. The rest of this guide will focus primarily on natural gas furnaces.

Starting With Heat

All furnaces must generate heat, which starts when the thermostat signals that the house is getting cold. This signal tells the furnace to light the fuel and start producing heat.

There are three different types of igniters your system may use. The oldest igniter is a pilot light, which is a small flame that burns continually inside the burn chamber. Next, there’s a direct spark igniter, which creates a spark when the system is lighting the fuel. The final, and most widely used igniter in modern furnaces, is the hot surface igniter. This has a ceramic “plug” that heats up through an electric current, similar to a light bulb filament. Once it’s hot enough, the fuel starts and ignites.

It’s not actually the flame that heats the air, but the exhaust created when the fuel burns. This exhaust travels up through the heat exchanger and then vents out through the flue.

Understanding the Heat Exchanger

The heat exchanger is a critical part of your furnace system. This is a series of tubes carrying the exhaust up from the burn chamber to the exhaust vent connector. The air circulating through the system absorbs the heat from the heat exchanger then circulates it out into your home.

Aside from the risk of a fuel leak, gas furnaces also pose a risk for carbon monoxide leaks. This happens because the heat exchanger is made of metal, which experiences repetitive heating and cooling. If the heat exchanger overheats, such as if there’s an airflow restriction, it weakens that metal. Once that happens, the exchanger may develop a leak, allowing the exhaust out into your home rather than venting properly.

Cracked heat exchangers sometimes go unnoticed until it creates a problem. However, in some cases, you may hear a rattling sound, but only as the unit first starts the heating cycle. You may also smell a strong, unpleasant odor that some compare to formaldehyde. Finally, your carbon monoxide detector may go off. The best way to catch a cracked exchanger is through annual maintenance, when a technician will inspect the component.

Circulating Air

Once the unit generates heat, the system circulates air to absorb that heat and move it into your home. The circulating fan is the component primarily responsible for making this happen. It draws the air in through the cool air return vent, through the system, and pushes it back out into your home.

To properly heat your home, the system has to create air movement throughout the space. Otherwise, the hot air would come from the vents, leaving cold spots around your home.

To create this circulatory movement, your system creates different pressures throughout your home. At the registers, the system creates low air pressure by drawing in the air. Conversely, at the supply vents, it has high pressure due to the air moving out. Gases move to equalize pressure in the space it occupies. As the air equalizes the pressure, it also moves the heat around your home.

Understanding Efficiency Differences

As you look at furnaces, you’ll notice there is quite a range of efficiency ratings. This efficiency comes from two primary factors: how it burns the fuel and how it runs the fan.

Lower-efficiency models are basically on or off systems. The burner has a single flame and flame height, and the fan has a single speed. This essentially makes the system frequently run on high. While this heats your home quickly, it also uses the most fuel and electricity.

At the other end of the spectrum are high-efficiency models, which have both a modulating burner and variable fan. This provides exactly the right amount of air circulating and the amount of heat needed to warm your home.

High-efficiency models also have a second heat exchanger. This means the air absorbs more heat from the exhaust, so you lose less through the vent. The added bonus to this is that the exhaust is cooler when it vents out, so there’s less concern about heat damage.

Degrading Performance Over Time

Like any mechanical system, your furnace’s performance will degrade over time. This includes reduced airflow and less heat transfer at the heat exchanger. You can prevent this performance degradation if you take the steps to keep your system properly maintained.

The first step to maintaining your furnace is regularly changing your air filter. For systems with the common 1- and 2-inch filter, you can expect to change it about every 90 days, on average. This time frame extends for the thicker 3- to 6-inch filters. However, some seasons may require more frequent changing, so plan to check the filter monthly, and gently vacuum off the loose dirt.

The next step is to get regular maintenance on your system, usually every fall before you start using it. During this maintenance job, technicians will tighten mounting hardware and electrical connections to reduce operational strain. They’ll also clean the heat exchanger and circulating fan, which notoriously collect the particles that get past your air filter. As mentioned earlier, they inspect your heat exchanger to ensure it hasn’t cracked.

Finally, they’ll test your system to ensure every stage of the cycle initiates properly. During this testing, they look for signs of suboptimal performance so that you can resolve it before it adds strain as your system runs.

When you need heating or cooling services, call the company people around Burbank have trusted for over 20 years. Our experts at Air Max HVAC provide heating and air conditioning installation, replacement, maintenance, and repair with indoor air quality audits and solutions. Call to schedule your furnace repair or maintenance with one of our dependable technicians today.