Why and How to Provide Make-up Air for Range Hoods

When you plan a kitchen renovation, it is important to visit your range hood dealer to decide what size of range hood will be required and then determine whether it is necessary to make provision for what the dealer has called “make-up air.”  The problem is that you don’t exactly know what is meant by “make-up air” and therefore don’t know how to determine whether your kitchen will need it. And if your kitchen does need make-up air, you also don’t know how to provide it for your range hood.

What is make-up air?

Make-up air is fresh air that is “brought into” the kitchen to replace the air that is being removed by a range hood. The larger the cubic feet per minute (CFM) airflow of the hood, the more air has to be replaced by make-up air. Formulas and legal requirements determine when a make-up air system is needed. An HVAC expert can install the right make-up air system.

In this article, I’ll discuss when and why your kitchen needs a make-up air system, how a make-up air system works, and also have a look at a method of how make-up air can be provided to your kitchen.

What is meant by “make-up air” and “make-up air system” for your range hood?

If you have a range hood installed in your kitchen, you usually use it every time you prepare food on your cooktop. The range hood removes air that is contaminated with grease particles from the food you are preparing. It also removes the odors associated with cooking. Simply put, your range hood extracts “bad” air from the kitchen and exhausts it outside your house. 

But if you extract air from the kitchen, the air has to be replaced. The replacement can be a “natural” process when fresh air is, for instance, coming into the kitchen from an open door or window. The fresh air coming into the kitchen from outside is called “make-up air.” 

However, when the volume of air extracted from the kitchen is more than the volume of air coming into the kitchen naturally, a make-up air system should be installed in your kitchen to ensure that the right volume of fresh air enters the kitchen. 

When do you require a make-up air system?

You’ll require a make-up air system if it is legally required according to the building regulations of the area where you live and also when your kitchen is not designed to have a lot of fresh air flowing into the kitchen naturally. A make-up air system will also be a good idea if you run your range hood fan quite frequently and for long hours. But let’s look at more details. 

1. Legal regulations regarding CFM capacity might make it compulsory 

As I’ve mentioned above, a make-up air system is needed when a greater volume of air is extracted from your kitchen than the normal natural inflow of fresh air. In most states of the US, there are regulations in place to make it compulsory to install a make-up air system if the range hood is removing more than 400 cubic feet of air per minute (CFM). 

Most gas range and cooktop manufacturers recommend range hoods capable of well over 400 CFMs when you have more than 4 burners on your cooktop. In practice, it means that any kitchen with a cooktop accommodating more than 4 burners should have a range hood extracting 400 or more cubic feet of air per minute and thus also might have to install a make-up air system if it is legally required by the authorities in your area. 

2. A small kitchen might make it legally compulsory 

Some states in the US also implement a regulation to make a make-up air system compulsory if the volume of the kitchen is not at least equal to 20 times the CFM capacity of the hood fan. This means that if you have a small kitchen, you might need a make-up air system even if the hood’s CFM is less than 400.  

To explain this principle, look at the following example:

According to this formula, you need a kitchen of at least 6,000 cubic feet if your range hood uses a 300 CFM fan (300x 20 = 6,000).  Suppose your small kitchen’s ceiling is 12’ from the floor, your kitchen floor must be at least 500 (6,000 divided by 12) square feet – roughly 23’ x 23’. If your kitchen is smaller, you need a make-up air system.  

3. A poorly ventilated kitchen that can benefit from a make-up air system

If a lot of air is not moving naturally through your kitchen, it might happen that more “bad” air is being extracted by the range hood than the volume of fresh air coming into the kitchen. A make-up air system will contribute to the fresh air inflow into the kitchen. 

4. If the range hood runs for several hours at a time

The longer your range hood is continuously extracting “bad” air from your kitchen, the more fresh air is needed to “fill the space.” Remember, the rule of thumb is that the same volume of air that is being exhausted has to be replaced with fresh air. A correctly installed make-up air system can provide this. 

How is a makeup air system installed and how does it work?

Installing the system

Although there is more than one way to bring make-up air into a building, I’ll only briefly discuss the most commonly used method in homes. 

To install the make-up air system (sometimes called “make-up air kit” or “make-up air unit”) the contractor will cut a hole in an exterior wall of your house. An 8” duct work will then be inserted in such a way that it runs directly into the kitchen area – if possible, about 10 feet away from the range hood. The damper is installed into a separate duct which is independent of the range hood ducting.

Here is an example of a makeup air kit

Inside the vent, an electronic damper is installed, which is connected to your range hood switch.  Whenever you turn on your hood, switch the damper inside the duct open to allow air to flow from outside into your kitchen.  This is the ”make-up air” that balances the air pressure inside and outside your house.

Is a ventilation system also a make-up air system?

Because your home most probably has ducts for your range hood and other devices, it doesn’t necessarily mean that your house is equipped with a make-up air system. Even if your home is equipped with a heating or cooling forced-air distribution system, it is still not a make-up air system. 

As described earlier in this article, although the make-up air system’s damper is always being activated by the range hood switch, it is an independent system with its own ducts with the sole purpose to bring fresh air from outside your home into your kitchen to keep the inside and outside pressure balanced. Thus, a ventilation system is not a make-up air system!

Problems with not having sufficient make up air

After reading this article up to here, you might now understand what make-up air is and be aware of the legal regulations regarding make-up air systems, but you still don’t fully understand why it is so important to keep the air volume in your kitchen at a specific level. So, let’s now have a look at some of the most important reasons why it is important to have make-up air.

1. Your range hood becomes less efficient if no make-up air is coming into the kitchen 

Negative air pressure is when the air pressure outside your house is higher than the air pressure in your kitchen. Your range hood is designed to work efficiently in a positive air pressure environment. 

If there is negative pressure in your kitchen, it can become impossible for the range hood to extract air and perform efficiently. The reason is that the interior air is pushed back into the kitchen when the higher-pressure outside air is trying to get in. 

As the amount of pressure between the interior and exterior widens, the situation develops where the range hood can no longer move any “bad” air out. That is when the air in your kitchen starts to feel musty or “heavy.” 

2. Doors’ functioning might be influenced 

Another impact negative air pressure might have is that inward-facing doors open quickly and outward-facing doors become hard to open. Air drafts can also develop making your home uncomfortable. 

3. Your energy bill can rise

Because your range hood fan has to “work harder” in a negative pressure environment to remove the “bad” air from your kitchen, it uses more energy. And as you know, the more energy your devices are using the higher will the energy bill be.  

4. Carbon monoxide levels in your kitchen might increase

As the air pressure between the interior and exterior of your home widens, it might get to the stage where when you turn on your range hood, air could be drawn down a fireplace chimney. This can cause smoke to enter your house. The negative pressure in your home can even cause air to be drawn down a gas water heater exhaust vent. When this happens, there is a possibility that dangerous carbon monoxide can enter your living space. 

Frequently Asked Questions

Are there sometimes legal obligations to install a make-up air system in a domestic home?

Yes, in most states of the US there are building regulations making the installation of make-up air systems compulsory under certain conditions.

If I don’t have a make-up air system in my home but sometimes need to depressurize my kitchen, what can I do?

To quickly depressurize your kitchen, open one or more windows, preferably near your range hood. Or you can keep your kitchen door open. Any of these two actions will equalize the air pressure between the interior and exterior spaces and thus depressurize your kitchen. 

Will a make-up air system in my house also improve the general air quality in my home?

Yes, because the make-up system provides fresh air from the exterior of your house to fill the “space” left as a result of the extraction of the “bad” air, it will improve the quality of the air inside your home. It will also prevent depressurization.

Conclusion

With the information you’ve received in this article, it will now be easier for you to determine whether you need a make-up air system with the new range hood you are installing.  The important aspects to remember are the following:

  • In most states in the US building regulations are making make-up air systems compulsory for homes under certain circumstances.
  • If enough make-up air is coming into your kitchen your range hood will work more efficiently and your energy bills will not unnecessarily escalate.  
  • The air in your kitchen will always be fresh and without odors.

Charles John

Experienced HVAC technician with 8 years of experience in the industry. Capable of handling all sorts of heating and cooling equipment as well as proficient in operational management, construction-related techniques such as preventative maintenance, electrical troubleshooting and AutoCAD

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