Does a Furnace Need a Fresh Air Intake? - Home Inspection Insider (2022)

Does a Furnace Need a Fresh Air Intake? - Home Inspection Insider (1)

With the constant evolution of furnaces and the architecture of homes in general, fresh air intake is a confusing one for many homeowners. What is the actual function of these systems? Are they still necessary today?

Furnaces need a fresh air intake because they are typically designed to push air out of the home while functioning, no matter the type installed. With the fresh air intake installed, you can ensure that the furnace’s combustion will not reduce your home’s air quality.

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(Video) Does my furnace need a FRESH AIR INTAKE?

The rest of this article will take a closer look at what fresh air intake means and how they are essential for maintaining your furnace’s efficiency. You’ll also see how fresh air intakes are important to the indoor air quality in your home.

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Fresh Air Intake Explained

As the name implies, a fresh air intake is a channel designed to draw fresh air into your home from outside. Most of the time, the fresh air intake is a duct that runs from a vent outside into the room housing your furnace. The exact locations and the number of fresh air intakes will vary in different homes, especially in regions where building codes dictate how air is released from the home.

Building regulations that control air loss are there to ensure that your property is energy efficient and conserving energy resources, thus ensuring that you contribute your quota in the fight against climate change. They are also designed to make sure that your home is properly ventilated at all times.

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These regulations support the installation of fresh air intakes because they play an important role in keeping your home ventilated, especially while a furnace is used.

Why Is a Fresh Air Intake Important for Furnaces?

Furnaces need oxygen to run, so they need as much fresh air as possible. Without fresh air intake, the furnace will use up the air in its immediate environment. To understand this better, you need to know how the various types of furnaces work.

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Standard-Efficiency Furnaces

They have also known as conventional or 80% furnaces, as they have a rating of 80 in their annual fuel utilization efficiency (AFUE). The rating means that such furnaces lose 20% of the natural gas energy that can be utilized for heat during combustion as a result of venting.

Standard-efficiency furnaces work by drawing air from their immediate surroundings. Think of this as some sort of equipment in the middle of your room with a fan channeling air into it and a vent connected from the top of the equipment to the outside carrying out the excess air. This means that your room is being stripped of the air in it, thus creating negative pressure.

The design of these furnaces is such that they will draw air away from your home regardless of what you do. Your focus should be on figuring out where the fresh air will come from. This is where the fresh air intake comes in. If you have one, the air pumped out of your home by the furnace will be replaced almost immediately by the fresh air intake, which draws air from the exterior.

If you are using a conventional furnace without fresh air intake, the air in your home will come from crawl spaces, dryer vents, attics, and other such sources as your furnace runs. This will negatively impact the indoor air quality as air from these spaces is often laced with contaminants.

Apart from worsening the air quality in your house, a standard-efficiency furnace running in a space where there’s no fresh air intake won’t function at optimum efficiency. This is because its blower motor will require more electricity to keep up with the demands of powering the process, and it will also generally run slower.

Additionally, the air sucked in from your attic and other similar sources also typically contain a higher level of contaminants with corrosive properties, which can cause the corrosion of parts inside the combustion chamber of your furnace—especially the heat exchangers and the burners. This reduces the lifespan of the furnace.

High-Efficiency Furnaces

High-efficiency furnaces are becoming more popular today. They are sometimes referred to like 90% furnaces to reflect their AFUE rating, which is 90. This means that such furnaces lose 10% of the natural gas energy that can be utilized for heat during combustion as a result of venting.

The confusion about whether or not to use fresh air intakes is often most visible amongst people that have installed this type of furnace. This is because these 90% furnaces feature a special pipeline that runs straight from an exterior vent into the furnace’s combustion chamber, which is sealed.

They also come with a vent outside of the property to dispose of the gases generated while the furnace is working.

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The architecture of high-efficiency furnaces means that they have their own fresh air intake. This means that they don’t use the air inside your home; rather, they draw air from outside. However, this doesn’t mean you don’t need an external fresh air intake because you’ve installed a 90% furnace. Indeed, these furnaces don’t cause the poor indoor air quality problem, but they pose a different concern.

Homes that have 90% furnaces are typically vulnerable to excess moisture. This is not a problem in conventional furnaces, as the open flue allows moisture to escape easily.

For information on SEER ratings and high-efficiency heat pumps, see our article Complete Guide to Heat Pump SEER Ratings.

Should You Block Fresh Air Intake During the Winter?

For many homeowners, blocking fresh air intake during the winter sounds reasonable as it is counter-intuitive to allow cold air in while you are trying to heat any space. This is why you will find many people stuffing the fresh air intake with rags, insulation, or any other materials that they feel can prevent the draft from coming down the fresh air intake duct.

Does this describe you? Then you need to rethink your approach, especially if you have a conventional furnace. Fresh air intakes are designed to ensure your furnace is working effectively and make sure your home is properly ventilated. If you block it off with a rag, then make sure your furnace is not running. Otherwise, there is a high chance of toxic fumes, including the deadly carbon monoxide, flowing back down your flue vent.

Your furnace is designed to work in the presence of any draft that might be coming down the fresh air intake and will most certainly neutralize it.

On the other hand, if you own a 90% furnace, you may think it is a good idea to block the fresh air intake since there is little to no risk of carbon monoxide poisoning. Unfortunately, the excess humidity caused by the trapped moisture can cause a range of health concerns, including the following:

  • The growth and spread of bacteria and viruses
  • Higher levels of indoor allergens such as dust mites and fungi
  • Exacerbation of respiratory conditions such as asthma
  • Increase in airborne chemical contaminants such as formaldehyde

Conclusion

Fresh air intakes are necessary for any home that has a furnace. Whether you have a conventional furnace or a high-efficiency option installed, there are downsides to not having a functional, fresh air intake.

These risks may seem more pronounced with standard furnaces, but the health hazards are every inch as dangerous on the newer furnaces. Fresh air intakes are there to keep your home properly ventilated, so don’t block them.

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Some heat pumps use a fresh air exchanger. For more information, see our article Do You Need an Air Exchanger with a Heat Pump?

FAQs

Is furnace fresh air intake necessary? ›

Furnaces require a fresh air intake since they are built to push air out of the house. By installing a fresh air intake, you can be rest assured that your furnace's combustion will not compromise your home's air quality or warrant frequent Lennox furnace repair near me.

Do all HVAC systems have fresh air intake? ›

Most home heating and cooling systems, including forced air heating systems, do not mechanically bring fresh air into the house. Outdoor air enters and leaves a house by: natural ventilation, such as through open windows and doors.

How do I know if my furnace has a fresh air intake? ›

Fresh Air Intake: If there's a screen, it's an intake. This is where the cool fresh air makes it's way back to your HVAC equipment. You can test this by turning on the furnace and feeling the suction as it draws air in. Exhausts: If the vent has a flap, it's an exhaust.

Where does my furnace get fresh air from? ›

And I'll just show you real quick what I was looking out there. So here's the mechanical. Room where

Can the furnace air intake be inside? ›

All venting systems must be installed according to local gas codes and manufacturers installation instructions. There is no real concerns with having the intake air being drawn from the inside of the structure.... in most cases. As long as your house does not severely go into negative pressure you will be fine.

Does a furnace need a cold air return? ›

No furnace can adequately operate without sufficient return air supply. We can think of a furnace as lungs. It 'breaths out' hot and it 'inhales' cold air. Air return vents are necessary for the 'inhale' process.

Does fan on furnace bring in outside air? ›

Whenever the fan runs, some ambient exterior air (hot/humid/cold/dry) will be mixed into the circulating air in your system.

Does furnace pull air from basement? ›

When the furnace fan comes on to push cold air through the duct, the hole you describe would pull more air from the basement than from the rooms. As the system tries to push more air into rooms that are not losing air, resistance would build. The result is you won't get the cooling comfort you seek.

Does fresh air intake help with humidity? ›

Adding a fresh air return decreases the negative pressure on the home. This stops humid air from being sucked in to wall cavities etc. That's good.

What happens if furnace intake is blocked? ›

If the intake pipe becomes blocked, the heating system will likely stall and turn off as it can't pull in the required air for the combustion process. If the exhaust pipe becomes blocked, a safety mechanism should trip to prevent dangerous fumes from entering your home.

How often should fresh air intake run? ›

It is recommended that you run your air to air exchange system several times per day, leave them on for 15 to 20 minutes and turn them off again. It's also a good idea to run this system if you have excess amounts of humidity, cooking odours, and when other indoor contaminants are present (e.g. cleaning supplies).

What is the purpose of fresh air intake? ›

Fresh air intake vents help our gas appliances in our homes breathe easier by bringing outside air into the home. In addition, fresh air intake vents help prevent carbon monoxide build-up in our homes. Today, homes may or may not have fresh air intake vents.

Where do you put fresh air intake? ›

The air inlet should be located high enough above the ground, or roof surface, to prevent accumulated snow from piling up over it, rainwater from splashing into it, and plants from growing into it. It should be located outside, not in an attic, crawlspace, garage, or attached dwelling.

Where is the fresh air intake vent? ›

Identify Fresh Air Intake Vents on Your Home - YouTube

How far does a fresh air intake need to be from exhaust? ›

Makeup air intakes should be placed to avoid recirculation. Grease- and explosives-bearing ducts, combustion vents, and refrigeration equipment have special requirements: intakes should be at least 10 ft from combustion or plumbing vents and exhaust air outlets, and be at least 10 ft above a road.

Should cold air returns be open or closed in the winter? ›

Open Low Returns in the Winter

In the winter, open your low returns. That allows your HVAC system to pull out the cold air that has collected at your floor.

How close can a cold air return be to the furnace? ›

Returns must be min. 10ft from furnace and cannot be located in a small volume space. See the IRC for the simple formula. Supply and returns must be sized for the space and balanced.

What is a cold air return on a furnace? ›

The answer may be your return air grills- also known as “cold air returns”. These are the vents that are usually on the wall and they do not have a control mechanism to open or shut their flow. Their purpose is to allow air to return to the furnace to be heated or cooled.

Can a furnace be in a closed room? ›

Enclosed spaces increase your risk of exposure to flue gas, which includes toxins like carbon monoxide. Your furnace needs combustion air that comes in through the ventilation systems for a safe and effective burn.

How much airflow does a furnace need? ›

A direct-vent furnace requires about 50 cubic feet of air for every 1000 BTUs of fuel input. The label or documentation with your furnace or water heater can tell you the BTU fuel input.

Do I need an air return in my basement? ›

I recommend that all basements should have at least 2 supply registers and 1 return register in the basement/equipment area just to keep that area slightly warm or cool and the air fresh. If you are going to finish that area to be used as living space, then more supply and returns will be needed.

Will opening windows in winter increase humidity? ›

When the weather outside is cold, the air is usually dry. Opening the window during dry, cold weather will reduce humidity levels inside the home or office and would be counter-productive. Keep the windows closed during cold weather and use a humidifier to keep humidity levels optimal.

Why is my house so moist? ›

Why Is My House So Humid? Several factors contribute to the humidity levels within a home such as the design, construction and materials, vapor retarder use, insulation, and how airtight the property is. Of course, the surrounding climate and temperature also have a direct effect on humidity.

Does opening window in winter reduce humidity? ›

When the humidity level is higher inside than outside, you can reduce the humidity in your home by opening a window. Opening the window increases the circulation of dry air in your home and prevents excess moisture from damaging various elements.

What happens if furnace intake is blocked? ›

If the intake pipe becomes blocked, the heating system will likely stall and turn off as it can't pull in the required air for the combustion process. If the exhaust pipe becomes blocked, a safety mechanism should trip to prevent dangerous fumes from entering your home.

How often should fresh air intake run? ›

It is recommended that you run your air to air exchange system several times per day, leave them on for 15 to 20 minutes and turn them off again. It's also a good idea to run this system if you have excess amounts of humidity, cooking odours, and when other indoor contaminants are present (e.g. cleaning supplies).

What does a fresh air intake do? ›

A filtered fresh air intake system adds fresh air to a home heating and cooling system. This improves indoor air quality by diluting polluted or stale indoor air and also pressurizes the home to help keep pollutants out.

Does fresh air intake help with humidity? ›

Adding a fresh air return decreases the negative pressure on the home. This stops humid air from being sucked in to wall cavities etc. That's good.

How do I clean the furnace intake pipe? ›

How to clean house fresh air intake vent - YouTube

Which pipe is intake on furnace? ›

Look for your furnace intake pipes, which are often white or black PVC pipes that exit a wall close to your furnace. Find where the intake pipes exit on the outside of your house. They are close to where your furnace is on the inside.

Does furnace pull air from outside? ›

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.

How many minutes of fresh air does a house need? ›

To exchange the air in a house, the average is 1 to 2 air changes per hour or between 60 and 30 minutes. This is known as the air exchange rate and that amount of time needed can vary. With open doors and windows, the rate is about 4 changes per hour, meaning that it takes only 15 minutes.

Where do you put fresh air intake? ›

The air inlet should be located high enough above the ground, or roof surface, to prevent accumulated snow from piling up over it, rainwater from splashing into it, and plants from growing into it. It should be located outside, not in an attic, crawlspace, garage, or attached dwelling.

How does a fresh air intake work on HVAC system? ›

What is a Fresh Air System and to install it. - YouTube

Will opening windows in winter increase humidity? ›

When the weather outside is cold, the air is usually dry. Opening the window during dry, cold weather will reduce humidity levels inside the home or office and would be counter-productive. Keep the windows closed during cold weather and use a humidifier to keep humidity levels optimal.

Why is my house so moist? ›

Why Is My House So Humid? Several factors contribute to the humidity levels within a home such as the design, construction and materials, vapor retarder use, insulation, and how airtight the property is. Of course, the surrounding climate and temperature also have a direct effect on humidity.

Does opening window in winter reduce humidity? ›

When the humidity level is higher inside than outside, you can reduce the humidity in your home by opening a window. Opening the window increases the circulation of dry air in your home and prevents excess moisture from damaging various elements.

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