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How a Furnace Works: 13 Things You Need to Know

Have you ever wondered how a furnace works? Well, it’s really cool . . . well, hot. Unless it’s not working, then that’s not cool.

Even though furnaces and air conditioners can be a little intimidating. The more you understand about how a furnace works, the better-prepared you’ll be when it comes to making repair or replacement decisions.

Now, for ease of explanation, we’ve broken your furnace down into two main parts:

  • The furnace where the air gets heated.
  • The living space where the warm air is distributed throughout the house.

Even though there’s more to how a furnace works than the basics we’re going to go over today, this should give you enough information to answer the question, how does my furnace work?

  1. CIRCUIT BOARD
  2. INDUCER MOTOR
  3. IGNITOR
  4. GAS VALVE
  5. FLAME SENSOR
  6. HEAT EXCHANGER
  7. EXHAUST VENT
  8. COMBUSTION AIR
  9. BLOWER FAN
  10. FILTER

Now, this is a high-efficiency unit, you can tell because it’s got PVC piping for the combustion and the exhaust. If this was not a high-efficiency furnace, you would notice a metal vent going out of the top and you might notice louvered doors because that’s how it brings the combustion air in.

Either way, if yours is high-efficiency or not, the information we will tell you about how a furnace works will apply to either one.

In the living space, you’ll find:

  • Thermostat
  • Supply Vents
  • Return Air Vents

There are a lot of things that have to happen in a very specific order in order for your furnace to work. I’m going to try and strike a balance between not enough information and too much information. Hopefully, it’s just right.

Now, back to how a furnace works! It all starts when the temperature in a room drops below the thermostat setting. The thermostat sends a signal to the circuit board calling for heat. The inducer motor turns on and draws combustion air into the furnace. This helps to make sure the gas is burning efficiently.

Next, an ignitor will either glow or spark to ignite the gas that starts flowing. This gas ignites into flames while the hot air and obnoxious gases are drawn into the heat exchanger. To make sure that the gas ignites, there’s a flame sensor that’s placed right into the path where the flame should be. If a flame is detected, the heating process continues while all of the hot air is being drawn into the heat exchanger. The heat exchanger gets very hot and as the air blows across it, it heats up and is blown out through the house. 

Before we get to that, we need to talk about where the fumes, gases, and carbon monoxide goes. The heat exchanger tubes have openings on either end. The flames superheat the air that enters into one end, then all of the dangerous gases exit out the other end which is connected to an exhaust which vents outside of the house. 

Back to the air that’s blowing across the heat exchanger. This is the real secret of how a furnace really works. With help from the blower fan, the cool air in the home is drawn through the return vents, through the filter, and across the heat exchanger. Then, the newly warmed air is blown through the ducting and out the supply vents all-around your home. The air cools off and is drawn back through the return vents and the process repeats itself until the room is warm enough and the thermostat sends a signal to stop. And that’s how a furnace works!

These 13 things are designed to work together and if even one of them stops working, you can experience a variety of problems, most of which result in your furnace blowing cold air (which is not what you want in the middle of winter)

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Our pricing is fair and transparent. We use a fixed-price guide that reflects the time, materials, and real costs of running a dependable home services business. No hourly rates. No inflated prices based on where you live. We focus on what it takes to get the job done—not on how much we can charge.

Before we price your drains or excavation project, our expert technician will perform an in-home assessment to evaluate the tasks required. We only charge for what’s necessary—no fluff, no extra costs. This allows us to pinpoint areas where we can save you money without sacrificing quality.

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We prefer to price based on the job and not what other companies charge. Hourly rates can lead to unexpected costs for homeowners, making the final price unpredictable. By pricing the work itself, we make sure you’re only paying for what’s actually needed—keeping things fair and efficient.

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Requesting a quote is simple. Contact Any Hour Services, and we will assess your needs, providing a transparent estimate for the repairs.

We also provide FREE estimates and second opinions for major plumbing and excavation projects like repiping, sewer or water line replacements, remodels, and outdoor drain installs. Our team will evaluate the job in person, explain your options, and give you clear, upfront pricing. No hourly rates. No surprises. Just honest answers and expert service.

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We offer a $29 Drain Clear for single, easy-access drains. A licensed plumber will inspect the issue, clear out buildup like grease or debris, and get things flowing again. It’s a simple, affordable way to fix slow drains and help protect your plumbing from bigger problems down the line.

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Yes, we provide FREE estimates for sewer main line replacements. If you are looking to replace your sewer main line, one of our expert technicians will come to your home and inspect your sewer main line, before showing you your options. Call us if you have questions about replacing your sewer main line—we’re here to help!

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You can pay for your service with cash, check, or any major credit card. We collect, in full, upon completion of the project. If you would like to make monthly payments, we have many financing options available through 3rd party finance companies (On Approved Credit). Your technician can talk to you about your options when they give you pricing options for the work you want done.

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Our phone staff are not expert technicians, so they can’t quote prices that would be accurate to your project’s needs. A trained technician needs to see the job firsthand to give you a clear, upfront price. Quotes over the phone are a guess, and we prefer transparency over uncertainty.

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Ballpark prices can be misleading. Until we see the job, we can’t quote your final estimate accurately. Other companies may give an estimate range, but that often leads to additional costs and surprises later. Instead, we focus on giving you a fair price once a trained technician can assess the job properly.

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A: We have a small dispatch fee to send our technician to your home. They’ll arrive in a truck stocked with thousands of parts, ready to complete most jobs the same day. After a thorough evaluation, your technician will explain the issue, walk you through the recommended fix, and show you your options and final price. No hourly rates. No surprises. Just a clear, upfront price before any work begins.

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Pricing FAQ

A:

Our pricing is fair and transparent. We use a fixed-price guide that reflects the time, materials, and real costs of running a dependable home services business. No hourly rates. No inflated prices based on where you live. We focus on what it takes to get the job done—not on how much we can charge.

Before we price your plumbing job, our licensed plumber will perform an in-home assessment to evaluate the tasks required. We only charge for what’s necessary—no fluff, no extra costs. This allows us to pinpoint areas where we can save you money without sacrificing quality.

Call Now

A:

We price the job—not the clock. Hourly rates can be unpredictable, leaving you unsure of the final cost until the job is done. We believe in upfront, fixed pricing based on the work itself—not guesswork. You won’t pay for delays or mistakes, and we hold ourselves accountable to ensure there are no surprises.

Call Now

A:

We prefer to price based on the job and not what other companies charge. Hourly rates can lead to unexpected costs for homeowners, making the final price unpredictable. By pricing the work itself, we make sure you’re only paying for what’s actually needed—keeping things fair and efficient.

Call Now

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Water heater replacements vary. Often, older units require updates to meet safety standards. Common items missing from many water heaters are flexible gas lines, expansion tanks, earthquake straps, gas sediment trap, upgrade exhaust venting, etc.

For an accurate quote, one of our licensed plumbers will inspect your existing system and provide a FREE estimate.

Call Now

A:

Our phone staff are not licensed plumbers, so they can’t quote prices that would be accurate to your project’s needs. A trained plumber needs to see the job firsthand to give you a clear, upfront price. Quotes over the phone are a guess, and we prefer transparency over uncertainty.

Call Now

A:

Ballpark prices can be misleading. Until we see the job, we can’t quote your final estimate accurately. Other companies may give an estimate range, but that often leads to additional costs and surprises later. Instead, we focus on giving you a fair price once a licensed plumber can assess the job properly.

Call Now

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We have a small dispatch fee to send our plumber to your home. They’ll arrive in a truck stocked with thousands of parts, ready to complete most jobs the same day. After a thorough evaluation, your plumber will explain the issue, walk you through the recommended fix, and show you your options and final price. No hourly rates. No surprises. Just a clear, upfront price before any work begins.

Call Now

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Yes! We offer FREE in-home estimates for major projects like water heater installations, water softeners, and repiping—without any dispatch fee. Our licensed plumber will assess the job, explain your options, and provide a clear, fixed price. No surprises or hourly rates—just honest, reliable service. Schedule your FREE estimate today!

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No, our plumbers don’t quote a price until they have seen your plumbing project. Once they quote a price, it doesn’t change, no matter how long it takes. At any time, if you want to add more tasks to your plumbing project, your plumber will let you know how much it would cost to perform the extra work.

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You can pay for your plumbing service with cash, check, or any major credit card. We collect, in full, upon completion of the project. If you would like to make monthly payments, we do have many financing options available through 3rd party finance companies, OAC. Your plumber can talk to you about your options when they give you pricing options for the work you want completed.

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