Furnace Fresh Air Intake 101

Fresh air intakes are a key component the HVAC system utilizes to maintain a safe and comfortable indoor environment in your home. We are going to discuss what a fresh air intake is and how a properly installed fresh air intake can increase your unit’s efficiency, performance, and prolong the life of your furnace. We will also cover how fresh air intakes play a vital role in determining your home’s indoor air quality.

 

What is a fresh air intake?

 

A fresh air intake is exactly what it sounds like, a path for your home to take in fresh air from the outside. In many homes the fresh air intake is simply an open duct ran from an outside vent into a basement, or any room housing the home’s furnace. Fresh air intakes can be in multiple locations throughout your home, especially in newer homes built to modern building codes requiring homes to be much tighter than older homes.

 

Homes are built “tighter” to decrease the air lost from the building in order to create energy efficient structures in hopes that we can slowly decrease the stress on our aging power grid and conserve energy resources. The tighter design is also required because of the health implications of air pollutants that are drawn into older homes from attics, basements, and crawl spaces. Throughout this article we will take a close look at indoor air quality but first we will address the direct correlation between fresh air intakes and forced air furnaces.

 

Why do furnaces need a supply of fresh air?

 

The easy answer is oxygen is a key element in combustion, therefore, your furnace needs air. A gas furnace needs approximately thirty feet of air for every foot of gas used. This is roughly the equivalent of running a bathroom exhaust fan into your furnace’s combustion chamber.

 

However, the best answer is a bit more complex and requires us to delve into the different types of furnaces and look at the home as one giant ventilation system that the furnace is only a part of.

 

Conventional/Standard efficiency furnaces

 

These furnaces are also known as “80 percent furnaces” because they have an annual fuel utilization efficiency (AFUE) rating of 80. This means that 20 percent of the possible energy found in the natural gas that can be used for heat is lost during the combustion process due to venting.

 

Conventional furnaces draw air from the area immediately surrounding the furnace. Just imagine a box mounted in the middle of a room in your house with an exhaust fan pumping air into it and a vent carrying it up out of your house. All the air that your conventional furnace is venting creates negative pressure and cause air to be drawn in thru the path of least resistance.

 

The furnace is going to pump air out of your house regardless of you having a fresh air intake or not. The difference is where the replacement air will be drawn from. If you have a fresh air intake, the air is immediately replaced with fresh air from outside the home. Homes without a fresh air intake close to a conventional furnace will often draw air in from attics, crawl spaces, dryer vents, and a host of other unconditioned spaces that reduce the quality of the air you and your family breathe.

 

In addition to reducing the indoor air quality of your home, a conventional furnace in a small or restricted space without a direct fresh air intake will be less efficient because the blower motor will either run slower or use more electricity to keep up, depending on the type of fan motor.

 

Air drawn from unconditioned spaces often contain higher levels of corrosive contaminates that reduce the life of your furnace due to the burners, heat exchangers, and other components inside the furnace’s combustion chamber corroding.

 

Many homeowners block fresh air intakes due to their belief that venting cold air into a home they are trying to heat is counter-intuitive. Therefore, you will find the fresh air intakes in many homes stuffed with insulation, rags and other materials homeowners instinctively grab when they feel a draft coming from the open pipe duct they find in their basement or room containing the furnace.

 

The old saying goes, “Listen to your instincts, they are there for a reason.” In this case, don’t listen to your instincts because the fresh air intake is there for a reason!

 

Blocking the fresh air intake in a small or restricted space containing a furnace can lead to negative pressure and can cause a back-draft of toxic fumes and carbon monoxide to flow back down the flue vent.

 

High efficiency furnaces

 

These furnaces are also known as “90 percent furnaces” because they have an AFUE rating of 90. This means that 10 percent or less of the possible energy found in the natural gas that can be used for heat is lost during the combustion process due to venting. These types of furnaces have a dedicated pipeline that runs directly from an outside vent into a sealed combustion chamber of the furnace and a sealed vent to the outside of the home for venting the toxic fumes from the combustion process.

 

Due to high efficiency furnaces having their own fresh air intake, no air is drawn from inside your home. Since high efficiency furnaces draw air directly from outside, the furnace itself does not require a fresh air intake in order to replace inside air that otherwise would have been drawn from the room the furnace is located in.

 

However, this does not mean that your home does not need a fresh air intake just because you have a high efficiency furnace. The open flue on conventional furnaces better allow for the escape of moisture. Homes where conventional furnaces have been replaced with high efficiency furnaces are often susceptible to excess moisture that often forms on the windows and causes mildew. Especially in cases where the fresh air intake is blocked or removed due to the belief it is not needed because a high efficiency furnace has been installed.

Leaking ductwork and other gas appliances, such as gas hot water heaters, also create negative pressure that causes air to be drawn into the home. Even brand-new ductwork installed to the most current energy codes lose around 10% of the air flowing through it, most ductwork loses much more.

 

No matter what kind of furnace you have installed, the system will push air out of your home. A fresh air intake ensures the air being replaced is not from area of the home that reduces the indoor air quality of your home.

 

Indoor air quality

 

One of the very first things we do upon entering this world is breathe. The average human breathes in about eight liters of air a minute, totaling around eleven thousand liters of air a day. Yet, we seem much more concerned with what we take into our body thru eating or drinking than the massive amount of air we take in.

 

We are constantly bombarded by a public tidal wave of information constantly stressing the health benefits of eating unprocessed foods. On the same note, the use of water filters in the home and/or only consuming pre-filtered bottled water has become mainstream.

 

I think it is safe to say we, as a society, are becoming more aware of how important it is to manage the quality of what we do or do not put into our bodies. It is hard to dispute the idea that managing what one puts into their body lends to a healthier and higher quality of life.

 

While the amount of air filtration products and systems indicate indoor air quality awareness is on the rise, it never gets the attention it deserves because breathing air is something you did before you ever formed a complete thought. It comes to us so naturally we do not even consider its extreme importance until it is hindered.

 

The moment our breathing is hindered, whether it be from choking, the wind being knocked out of us, or struggling to get to the surface of the water, all thoughts are pushed from our mind and every molecule of our being is focused on one thing, taking a breath.

 

While starvation or dehydration can be similar at their peak, they both take a substantial amount of time to set in. The loss of the ability to breath sends us reeling in a mere instant. Yet, we give little thought to the quality of what our brain is so quick to let us know we need most to live, air.

 

The EPA cites studies that indicate the average person can spend close to ninety percent of their time indoors and that the air in most homes and buildings can be more seriously polluted than even the largest cities and most industrialized areas.

 

One of the most important aspects of indoor air quality is the replacement of stagnant air inside your home with fresh air. The air in your home should be recycled about five times per hour.

 

Fresh air intakes ensure that additional contaminants from the unconditioned spaces of your home are not being brought into the mix of air being circulated throughout your home.

 

We have covered what a fresh air intake is and how it is an integral part of your homes HVAC system. Having a properly installed fresh air intake is the first step to improving your home’s indoor air quality, and our parting tip is to double check that your fresh air intake is actually ran to an outside vent and not just terminated in the attic or some other inside space.

Steve De Vries is a “Red Seal” refrigeration technician with over 20 years of experience in the HVAC industry. He has been a certified Lennox Premier technician since 2006. Steve is also a Master gas-fitter licensed by the province of Manitoba. Along with his Red Seal Provincial accreditation he also holds an electrical license. Born and raised in Winnipeg Manitoba, Steve has a very good understanding of a diverse climate and the affects it has on our construction. Well versed in duct design, fabrication, ventilation, and air quality, Steve understands all the variables to take into consideration for our region as well as the science to achieve desired comfort, which is so much more than just temperature.