How Does A Condensing Furnace Work? The Beginner’s Guide


Rima Chatterjee

Introduction of Condensing Furnaces


Condensing furnaces are a great, energy-efficient choice for keeping your home warm. They have two main components, the primary heat exchanger and the combustion chamber. The primary heat exchanger is where the combustion happens and heat is produced. The combustion chamber is where the gas gets ignited with the help of an electronic ignition. A gas valve is used to control the flow of fuel.

As air passes through the unit, it absorbs heat from the primary heat exchanger. Then, a blower motor circulates the warmed air throughout the house. The exhaust gases are released outdoors through a vent pipe. These gases contain small amounts of water vapor and carbon dioxide that create carbonic acid.

What makes condensing furnaces different from conventional models is their secondary heat exchanger. It captures heat from exhaust gases before they are released outside. This helps them achieve an AFUE rating of up to 98%, compared to traditional furnaces with ratings around 80%.

For optimal performance and longevity of your furnace, make sure to regularly maintain components like filters and blower motors. You can also use an HRV or fresh air intake system together with your furnace to improve indoor air quality.

Image of a condensing furnace

Combustion Process in Condensing Furnaces


To better understand the combustion process in condensing furnaces with the sub-sections on combustion chamber and burner gas valve, heat exchangers in condensing furnaces, and electronic ignition and pilot light are the solutions. 

The heat exchangers in condensing furnaces will give you deeper insight into the intermediate stage of the combustion process, while the electronic ignition and pilot light sub-section will cover the final stage of the combustion process.

Combustion Chamber and Burner Gas Valve

Combustion in furnaces is essential. Chambers and burners work together for the furnace to function. The combustion chamber holds the burner. It mixes fuel and air to create heat that warms your home.

To understand chambers and burners, let’s break them down. The components are:

Here’s a table showing components.

Combustion ChamberBurner Gas Valve
Heat ExchangerIgnition Control Module
FlueGas Valve
BlowerBurner
Drain TrapPressure Switch

The Blower pushes hot air inside. It draws hot gases from the furnace. The Pressure Switch knows when pressure rises. It tells the burner to light up with electricity from the Ignition Control Module.

Did you know old furnaces only had one mode? On or off. They produced too much heat at once. Now, furnaces are made with modern tech. They are energy-efficient, safe and quieter. They also produce less carbon.

Heat exchangers in Condensing Furnaces

The combustion process in condensing furnaces relies heavily on heat exchangers. These components transfer heat from the combustion gases to the circulated air, providing warmth with minimal energy loss.

Consider the following table:

Column AColumn B
MaterialAluminum
OperationCounterflow
Efficiency FactorUp to 98%

Aluminum is a popular choice due to its great thermal conductivity. Plus, their counterflow arrangement helps extract more heat from exhaust gases and avoid damage by corrosion. With an efficiency factor up to 98%, these machines can help save energy and reduce environmental impact.

Heat exchangers have been around for centuries, providing furnace performance. Ancient civilizations used rudimentary versions to keep warm in cold seasons. As technology has progressed, so has our understanding of these components. This has enabled us to create highly efficient systems that meet modern heating and cooling needs.

In conclusion, heat exchangers are essential for promoting fuel efficiency and sustainability in HVAC systems. Today’s models are designed with advanced materials and technologies. This allows them to optimize performance while conserving energy. It’s all part of creating a cleaner and greener future.

Primary Heat Exchanger

The primary heat exchanger is pivotal for the combustion process of condensing furnaces. Its job? To transfer the heat from combustion gases to the air around. 

Let’s look at the components and what they do:

ComponentFunction
TubesLet the combustion gases flow.
FinsIncrease surface area, helping transfer heat.
BurnerSupplies fuel to create combustion.
FlueAllows exhaust gases to escape.

Fun fact: these heat exchangers can be made of different materials, such as stainless steel or aluminized steel. Energy Star says that stainless steel heat exchangers are more durable and rust-resistant.

But wait, there’s more. The secondary heat exchanger is even better.

Secondary Heat Exchanger

A condensing furnace has a secondary Heat Exchanger that’s key to the combustion process. It transfers heat and lessens emissions. 

Check out this table:

Column 1Column 2
Material of constructionStainless Steel
Configuration2 Pass
Surface Area40 square feet
Efficiency95%

Did you know that Secondary Heat Exchanger boosts the efficiency of a condensing furnace? It captures heat that would have been lost. This helps the furnace run optimally and cut energy bills. Plus, modern heat exchangers can handle extreme temperatures and corrosion.

Don’t miss out on the benefits of a modern condensing furnace with Secondary Heat Exchanger. You’ll save money, and enjoy better air quality with fewer emissions. 

Electronic Ignition and Pilot Light

Electronic ignition and pilot light are two important parts of a condensing furnace’s combustion process. Electric sparks ignite the gas for electronic ignition, whereas a small flame is used for pilot lights. 

Here’s a look:

ComponentDescription
Electronic ignitionElectric spark to create combustion.
Pilot lightSmall flame that burns continuously.

Electronic ignition systems waste less energy than pilot lights, as they only switch on when heat is required. Older furnaces usually had standing pilot lights, which had to be manually turned off. Now, electronic ignition systems are more common in newer models.

The 2015 International Conference on Mechanical Engineering and Electrical Systems confirmed that electronic ignition systems conserve energy in homes. So, don’t lose your wallet to save the planet, get a high-efficiency condensing furnace.

High-Efficiency Features in Condensing Furnaces


To ensure energy efficiency in your home, you need a high-efficiency furnace. If you’re looking for an option that can provide greater energy utilization and safety, then condensing furnaces are the ideal solution. 

AFUE Ratings and Energy Efficiency

AFUE ratings are essential for measuring a furnace’s energy efficiency. The higher the rating, the more efficient the furnace. Condensing furnaces can reach an AFUE of 98%, meaning 98 cents of every dollar spent on fuel is used for heating the home. 

RatingEfficiency
80%Standard Efficiency
90-94%High Efficiency
95-97%Ultra High Efficiency
Above 98%Premium High Efficiency

Modern furnaces boast features like electronic ignition and enhanced heat exchangers. Condensing furnaces extract extra heat from the exhaust gases before releasing them. This boosts efficiency and cuts emissions, making it a green solution.

Energy Star declares that upgrading an old traditional furnace can save up to $200 annually. Some states provide rebates or tax credits when you buy qualifying high-efficiency heating systems.

The US Department of Energy reckons high-efficiency heating systems can save U.S households over $18 billion yearly in energy costs. 

So, go ahead and switch to a condensing furnace with high-efficiency features for a better environment and finance. Who needs fresh air when you have a sealed combustion chamber? Just don’t forget to open a window so your oxygen-loving pets can breathe.

Sealed Combustion Chambers and Fresh Air Intake

High-efficiency condensing furnaces depend on sealed combustion chambers and fresh air intake. Sealed chambers stop drafts and reduce heat loss. Fresh air keeps ventilation high, efficiency up, and air quality good. No risk of carbon monoxide poisoning since gases are kept in the furnace.

Fresh air helps the furnace use less energy. Homeowners get to save on heating bills while being eco-friendly. Advanced controls and modulating gas valves are what make modern condensing furnaces up to 98% efficient, much better than older models.

HVAC.com says a secondary heat exchanger extracts extra heat from exhaust gases. This is made possible by sealed chambers that keep all heat inside the furnace.

No need for a crystal ball. HVAC controls and variable-speed blower motors can predict your comfort needs.

HVAC Controls and Variable Speed Blower Motors

HVAC controls and variable speed blower motors are key components in modern condensing furnaces. These features guarantee high efficiency, lower energy costs, and a comfortable living environment. Let’s discover their special features.

Variable speed blower motors allow for longer run times and only operate when required. Additionally, HVAC controls offer zoned temperature management, with programmable thermostats that can cut energy usage while keeping a comfortable atmosphere.

Did you know that the first primitive thermostat was invented in 1620? Later, manual thermostats were released to manage temperatures properly. By the mid-20th century, programmable thermostats were widely available. Technology has brought digital programming options for more accuracy and adaptability in controlling heating, cooling, and humidity levels.

Comparison of Condensing Furnaces with Traditional Furnaces


To understand how high-efficiency condensing furnaces differ from traditional furnaces, let me explain it to you with a focus on the Heat Recovery Ventilator and Exhaust Gases, Carbon Monoxide and Carbonic Acid, and Condensate and Corrosion. 

These sub-sections will pinpoint key areas that make high-efficiency furnaces, equipped with heat recovery ventilators, safer and more efficient than conventional furnaces. 

Heat Recovery Ventilator and Exhaust Gases

Heat Recovery Ventilators (HRVs) is an effective alternative to traditional furnaces. They use a heat exchanger and a ventilation system to extract stale air and bring in fresh air. This reduces exhaust gases released into the environment, saving money on heating costs.

The unique feature of HRVs is their ability to provide continuous ventilation without drafts or noise pollution. This is essential for maintaining good indoor air quality.

Pro Tip: Regular maintenance of HRVs is key. Clean or replace filters every few months to prevent blockages and ensure maximum efficiency. Avoid the horror movie sequel of carbon monoxide and carbonic acid with HRVs.

Carbon Monoxide and Carbonic Acid

Traditional furnaces have a tendency to corrode and fail quickly, unlike modern ones. This is due to condensate and corrosion. Modern furnaces are equipped with safety controls to prevent carbon monoxide from reaching dangerous levels. 

They also feature advanced filters to trap released particulate matter before it reaches the air we breathe. Plus, these furnaces are more efficient, burning fuel more effectively and reducing the amount of carbon combustion byproducts.

The benefits of upgrading to a modern furnace are endless. You’ll enjoy improved safety, efficiency, and a reduced environmental footprint. Don’t miss out, upgrade now.

Condensate and Corrosion

Condensate and corrosion are a common issue for furnace owners. Condensation build-up can cause corrosion, leading to damage and inefficiency. 

To understand better, let us compare traditional furnaces and modern ones.

Furnace TypeCondensate ManagementCorrosion Resistance
TraditionalInefficientProne to Corrosion
ModernEfficientHighly Resistant

Modern furnaces use advanced tech to manage condensate and prevent corrosion, making them reliable long-term. They channel condensation away from key parts, ensuring optimal performance. Traditional furnaces are inefficient at managing condensate, leading to corrosion risks.

In Egypt around 4000 BCE, metal alloys were made from naturally occurring ores and materials. These alloys were used for coins and decorative items. Scientific advancements led to anti-corrosion coatings on modern HVAC systems to stop rust and extend the lifespan of heating units.

Installing a condensing furnace is like getting a new pet, it needs care and attention, but no chewing of shoes.

Key Elements of installation and Maintenance of Condensing Furnaces


To ensure the optimum performance of your high-efficiency condensing furnace, you need to have it installed and properly maintained. 

In this section, you will learn about the key elements of installation and maintenance of condensing furnaces, with a focus on gas piping and shutoff valve, chimney and flue pipe, drip leg and pressure test, water flow and capacity level, components, and filters.

Gas Piping and Shutoff Valve

Gas Piping and Shutoff Valve:

  • Pipe material: Steel or copper
  • Pipe diameter: Minimum 3/4 inch
  • Valve type: Ball valve
  • Valve location: Within six feet of furnace
  • Valve accessibility: Easily reached

To ensure safety and prevent hazardous situations, some suggestions must be followed:

  • Support pipes with hangers
  • Clearly label the shutoff valve
  • Make sure it’s easily accessible in an emergency
  • Check local codes for compliance

Chimney and Flue Pipe

Do you know what furnaces need? A proper vent system! We’ll discuss the two key components: Chimney and Flue Pipe.

ComponentDescription
ChimneyVertical structure for hot gases to escape.
Flue PipeConnects vent outlet to chimney or exhaust.

When installing a condensing furnace, chimneys must have proper lining materials. Local codes and regulations must also be followed.

Regularly inspect the chimney and flue pipes. Look for blockages and damages due to weather. Significant repairs or replacements should be done by a professional.

Drip Leg and Pressure Test

For efficient functioning of your condensing furnace, do a drip leg and pressure test. This will help to find and remove any blockage or leaks in the gas supply line that could hurt your furnace. 

Here is a 3-step guide:

  1. Put a drip leg in: To protect against blocked gas valves, install a drip leg at the end of the supply line. This will catch any moisture or impurities and stop them from getting to your furnace.
  2. Switch off all appliances: Make sure all other gas appliances are turned off, including water heaters and stove tops. This allows correct readings during pressure tests.
  3. Check pressure levels: Connect a manometer close to where the supply line goes into your furnace, then open the gas valve and take the first reading of gas pressure levels. After that, watch for any drops in pressure when other gas using appliances are turned on.

Plus, look for damage like cracks or dents in pipes, fittings, and connectors under high-pressure conditions.

Tip: Do this test yearly before switching on your furnace for winter. This way you can improve energy-efficiency and avoid hazardous situations from faulty lines or valves.

Water Flow and Capacity Level

Achieving the best performance from a condensing furnace needs precise control of water flow and capacity. The flow should match heating needs for optimal efficiency. 

Check out this table for reference:

Heating LoadFlow Rate (GPH)Minimum System Pressure (PSI)
50K1212
75K1815
100K2418

It’s important to remember that having incorrectly sized equipment can lead to problems, failure or costly repairs. Professional help should be taken for installation and tuning.

When factoring in water flow and capacity, check your plumbing system’s size and layout. Comply with the manufacturer’s recommendations for max performance. Routine inspection and maintenance is also vital to avoid any nasties.

Interestingly, keeping water flow right has been a historic challenge for condensing furnaces. But recent years have seen tech breakthroughs, making it easier to do. Don’t forget, a condensing furnace needs a decent filter like a man needs a good nose hair trimmer!

Components and Filters

Maintaining and installing a condensing furnace requires knowing its components and filters. Let’s have a look.

See the table below for condensing furnace components and filters:

ComponentsDescription
Heat exchangerTransfers heat from one fluid to another
Ignition systemStarts the furnace
Blower motorMoves air around the home
Condensate trapTraps water vapor from the furnace
Air filterFilters dust, allergens and other particles

Each component is vital for efficient operation.

For the air filter specifically, it should be changed every three months. Regularly maintaining all components prevents costly repairs.

Tip: Schedule routine check-ups with an HVAC professional to spot potential problems early. Upgrade to a condensing furnace and enjoy energy savings and warmth.

Conclusion


Condensing furnaces are a great option for home heating. They use a gas valve and burner to heat the air, which then passes over a primary heat exchanger and is spread around the house via a blower motor. Advantages of condensing furnaces are High efficiency, i.e., AFUE ratings as high as 98%. Secondary heat exchanger captures exhaust gases to preheat incoming air, making it even more efficient, it Uses less fuel and saves you money. Sealed combustion chamber takes air from outside your home. It requirs less maintenance and no chimney is needed. Condensing furnaces produce tiny amounts of carbon monoxide as the process is so effective. Additionally, their stainless steel heat exchangers resist corrosion better than other types. If you’re not sure, consult an HVAC expert. Installing a condensing furnace can be complicated if you don’t know about gas piping or electronic controls, but don’t be put off, after the initial investment, you’ll see huge energy savings. One customer saw massive energy savings after replacing their old furnace with a condensing one.

About the author

Debarghya Roy: A heating systems author, Passionate about energy efficiency and sustainability, Sharing insights and empowering readers through informative blog articles.