Exhaust Fans: How They Work & Choosing the Right One

We need air to breathe, right? Well, so does your house, apartment building, or business space. Without a continuous replacement of air, the harmful contaminants in stale air (hello, carbon monoxide) can make you sick. 

Enter exhaust fans — ventilation tools with mechanical motors that remove moisture, odors, and pollutants from stale air and replace it with fresh air. You might find one in a kitchen, bathroom, or commercial space, but they often work in tandem with other HVAC systems in your home. 

Now, how exactly do exhaust fans work, and how do you sift through all your options? 

Don’t worry; I’ll walk you through everything you need to know about different types of exhaust fans, and how to choose the best exhaust fan option for you.

How Do Exhaust Fan Systems Work? What is Their Purpose? 

What do you think of when you hear about exhaust fans? 

Maybe it’s that giant ventilation device pumping air into a factory floor – or you’re thinking of a kitchen ceiling exhaust fan that ensures your fire alarm doesn’t go off. How about exhaust fans for garages in mechanic workshops? 

All of those are good examples of exhaust fan systems.

Different types of exhaust fans meet specific ventilation needs for a space. But the grand purpose remains the same: exhaust fans remove stale air from your bathrooms, kitchens or work spaces. 

An exhaust fan usually removes old air and sends it outside. But often, the exhaust fan is part of your building’s or home’s overall HVAC system. 

Why and how different areas exhaust can be confusing. So let’s take it step by step: 

  1. You want your house to be at a neutral or slightly positive pressure because you don’t want outside air to leak in (you don’t want the hot air in the summer or the cold air in the winter sneaking in). 
  2. But even though we want buildings overall to be positive pressure (so outside air–cold or hot–doesn’t leak in), we want our apartments to be at a slightly negative pressure. Confusing, right? I know, but just hang in there with us. 
  3. The air replacement theory in apartment buildings works like this: A Fresh Air unit, also known as a Makeup Air unit, pumps fresh, filtered, tempered air into the public corridors.  Inside apartments, kitchens and bathrooms have exhaust vents and are removing air out of the apartment and out of the building. 
  4. The exhaust in kitchens and bathrooms causes a negative air situation in your apartments. But the corridors have positive pressure. See where we’re heading? The positive pressure air filters under and around the front door and into the apartments. The clean air then goes through the apartment where it is eventually exhausted out through the kitchens and bathrooms. This is how we get constant air changes in apartments.

Having trouble distinguishing the two pressures? Think of it this way: imagine putting a large plastic bag over a small vacuum. Turning on the vacuum will suck (aka exhaust) all the bag’s air, causing it to collapse. No air = negative pressure. 

What happens if you blow into another plastic bag until it’s full? Positive pressure. And let’s say you connect those plastic bags. You can probably picture the air from the full bag naturally flowing into the empty one. 

Why do we want constant air changes? So we have clean fresh air in our apartments…and to avoid the lovely smells of our neighbors’ lives!

Exhaust fans, with the help of makeup air units, balance negative and positive pressure by infusing fresh air into one area and exhausting old air out. This results in a constant flow of fresh, filtered, tempered, and clean air.

Types of Exhaust Fans

Exhaust fans help you filter clean air into many different spaces. Let’s run through each type:

Kitchen Exhaust Fans

This is your standard kitchen over the stove exhaust fan. Apartments will typically have a wall register, which is part of a larger system, removing air from the room.

When was the last time you cooked a big feast? You had potatoes roasting in the oven, garlicky greens on the stovetop, and maybe some beef patties on the BBQ. Yum. 

I’ll bet some smoke was wafting through your kitchen, even if the window was open. Here’s the thing: tons of odors and emissions rise from cooking and fog up your indoor air quality. That’s right — your cook fest won’t just waft delicious aromas through the room. There’s carbon monoxide and formaldehyde mixed in unless you have an exhaust fan.

Kitchen exhaust fans help you achieve two crucial feats: 

  • Eliminate harmful chemicals in the air from cooking emissions and improve indoor air quality
  • Reduce smoke that might cause your fire alarm to go off

Commercial Exhaust Fans

If you’re running a commercial or industrial space, your employees may experience even worse air pollutants than in your average kitchen. Methane, carbon dioxide, and nitrous oxide are just a few chemicals that rise from fumes in day-to-day operations in manufacturing and processing plants.

It’s not uncommon to see super-large fans in these spaces to accommodate a greater need for air filtration. On top of exhaust fans, commercial buildings often use economizers — a mechanical device that helps reduce energy consumption. These devices aid in lowering hefty energy bills for commercial businesses. 

Now, how about large apartment buildings which produce the most greenhouse gasses of all buildings? You’ll usually see a large rooftop HVAC unit with adjustable grills on each floor. It blows fresh air into apartment corridors — specifically ½ cubic feet per minute, for every 1 square foot of corridor space. 

A tenant opens the apartment door, and boom — fresh air comes in while dirty air filters out through the unit’s kitchen and bathroom exhaust grills. 

This is how we constantly “replace” the air in our apartments.

Keep in mind that residential buildings might use makeup air units for public corridors and simple exhaust fans for kitchens and bathrooms.

Bathroom Exhaust Fans

Hopefully, the bathroom in your private home has a small exhaust fan to keep things fresh. This is required in most areas of the country.

Fans help remove odors as well as moisture and hot water vapor from hot showers. If you leave a bathroom long enough without an exhaust fan, all that moisture will eventually become mold buildup. Don’t scoff — that mold can make you sick and, ultimately, damage plaster walls and sheetrock. 

The average bathroom exhaust fan or system moves air at a speed of 50-300 CFM (cubic feet per minute). 

Industrial Exhaust Fans

Think of every hotel or apartment building you’ve visited. Hopefully, each bathroom had a little exhaust fan to air things out after you do your business. But that’s not always feasible for every property manager or hotelier. Instead, they have industrial exhaust fans that serve many bathrooms (or kitchens). 

These exhaust systems usually use industrial fans on the roofs to discharge stale or contaminated air from the building.

Here’s how you can visualize it: 

Think of a square or rectangle duct, starting on the bottom floor, traveling up to the top floor and out through the roof. This duct system might be 30 stories or higher! Each floor’s bathroom connects to the vertical duct through a boot or a sleeve. 

There is also an adjustable grill in each bathroom to let just the right amount of air out, usually 50 to 60 CFM. The roof’s industrial exhaust fan sucks the air out of each bathroom through the duct, and up to the roof where the exhaust fan discharges it.

The only time a bathroom or kitchen is not required to have a mechanical ventilation system (an exhaust fan) is if it has an operable window. But hey, we’re in New York. I haven’t seen a window in a bathroom since the 1970s, making exhaust fans absolutely vital.

Wall Exhaust Fan

Wall exhaust fans are typically used in commercial or industrial locations, sometimes for mechanical rooms in residential or commercial buildings.. They feature varied CFM speeds and propeller widths, but accomplish similar goals of filtering air in large spaces. 

Exhaust Fans for Garages

Cars have a long list of vehicle exhaust emissions, namely carbon monoxide, carbon dioxide, and nitrous oxide. Add hydrocarbons, benzenes, and particulates; your car has created a toxic cocktail right in your garage. 

Exhaust fans for garage spaces are vital for cleaning up the air and reducing moisture. Plus, they help reduce the odor from the trash during warmer months. Ever tried playing mechanic on a hot summer day? No thanks — unless you have an exhaust fan, please!

You might see garage exhaust fans wall-mounted, rooftop-mounted, or ceiling-mounted. 

Mushroom Fans or Roof Fans

Mushroom fans get their name from the appearance — a square base with a hooded, ridged mushroom-cap top. These fans are found on rooftops and help you regulate building temps while removing large amounts of dirty air from a space. 

Mushroom fans are workhorses — mostly down-blast fans, they’re often in use in buildings with multiple bathroom and kitchen duct systems. They get the job done but have a few downsides: 

  • Noisy: Pulleys, shafts, fan belts, and bearings move around loudly, with constant metal clanking and vibrations.
  • Inefficient: They consume so much energy because of the extra power needed to move air throughout its turbulence (a ¼ horsepower motor could use 500 watts of power and a ½ horsepower motor could use 800 watts of power).
  • Frequent service: You’ll be spending serious money on constant maintenance visits to lubricate bearings, adjust and align pulleys, or replace belts.

T7 Exhaust Fans

Now, imagine all the bells and whistles of a brand new exhaust fan with: 

  • 67% less energy consumption
  • 80% less in operational costs
  • Zero maintenance required
  • Minimal noise

Sounds like a dream, right? Not really — this is reality for Alternative Sustainability’s patent-pending High-Efficiency T7 Exhaust Fans. 

Our exhaust fans discharge air as directly as possible with curved ducts with inlet guide vanes — minimal turbulence and energy required. The T7-16 moves the same amount of air a typical ¼-horsepower motor mushroom fan moves, but with 150 watts instead of 500. Similarly, our T7-26 moves the same air as a ½-horsepower motor mushroom fan with 240 watts instead of 800. 

Using 67% less electricity, T7 Exhaust Fans help you save a ton of kWh — plus, they’re maintenance- and assembly-free. No motors or bearings to grease, no roofing work required, and no need to run new electrical and conduits. 

We tested our T7 Exhaust Fans, using them as replacements for 15 rooftop exhaust fans in one building. We saw a decrease of a whopping 63,000 kWh per year. On top of that, the vibration-reducing connections, water-tight screws, and duct insulation reduce noise to a minimum. 

In a world where sustainability and efficiency are becoming more vital, T7 Exhaust Fans are a must-have for any building.

Choose the Right Exhaust Fan

Today’s property managers, homeowners, and business professionals need flexible, sustainable HVAC solutions. And that’s what Alternative Sustainability delivers with our high-efficiency T7 exhaust fans. 

You can adjust the CFM anywhere from 200 to 3,200, save 67,000 kWh per year, and reduce your exhaust fan operating costs by 80%. 

Alternative Sustainability is the only company that guarantees its products will reduce a building’s carbon footprint, raise energy scores, and provide cost savings/ .

We have designed energy-producing devices that are changing the energy production picture, reducing carbon gasses, and helping buildings & homeowners save money – and we can do this with an ROI of 3-5 years. 

There are no other products that will help residential, commercial, or any other multi-unit building reduce their energy usage enough to meet new building energy requirements. Without these options, it will be almost impossible to avoid the new fees and fines that will be placed on buildings with energy usage over the legal limits. 

Alternative Sustainability doesn’t just provide products: we’re also energy consultants and building experts who can review your building and tell you exactly the changes you need to make to improve your energy consumption and lower your carbon footprint. And, we’re working with developers to design near carbon neutral buildings.

We can’t think of any suitable alternative — contact us today for a high-efficiency T7 Exhaust Fan!