A restaurant kitchen struggling with smoke buildup, a warehouse where doors slam shut due to air pressure issues, a hotel lobby with stale, stuffy air that guests immediately notice—these are all signs of ventilation problems—and they cost businesses money.

Without a make-up air unit replacing exhausted air, your building’s air pressure becomes unbalanced, forcing Heating, Ventilation, and Air Conditioning (HVAC) systems to work harder while air quality declines. Over time, that means higher energy bills, premature equipment failure, and even safety risks.

With 80 years of experience, Lee Company has helped businesses across Tennessee, Alabama, Kentucky, and Georgia resolve ventilation challenges. Below, we’ll explain make-up air, why it matters, and how the right system can protect your commercial building.

What is Make-Up Air?

Every time air is removed from a building — whether by exhaust fans, ventilation systems, or combustion processes — it needs to be replaced. Without a dedicated system to bring in fresh air, your facility can develop negative air pressure, causing doors to be difficult to open, air to rush in through cracks, and HVAC systems to work overtime to compensate.

A make-up air system is designed to replace the air that’s been exhausted, maintaining a steady balance of airflow throughout a facility. These units pull in fresh, filtered air from outside and distribute it throughout the building. Depending on the needs of the space, make-up air systems can be heated or cooled to match indoor temperatures, preventing uncomfortable drafts and maintaining efficiency.

Since HVAC systems account for 40% of total energy consumption in commercial buildings, with space heating alone making up 32% of that usage, balancing airflow is critical for controlling costs.

In large-scale operations like manufacturing plants with multiple exhaust points or commercial kitchens running high-output hood systems, even a slight imbalance can mean significant energy waste, leading to thousands of dollars in unnecessary operating costs each year.

Without proper replacement air, HVAC systems are forced to work harder to compensate for the lost air, leading to higher energy bills and premature wear on heating and cooling equipment.

Make-up air systems don’t work in isolation — they integrate with HVAC and exhaust systems to ensure that air pressure remains stable, indoor air quality is maintained, and energy waste is minimized.

For example, in warehouses or distribution centers with large roll-up doors, sudden changes in air pressure from frequent openings can disrupt temperature control and create a noticeable impact on worker comfort and safety. Whether in a commercial kitchen, warehouse, or large retail space, these systems help maintain a healthy and efficient environment.

Why Make-Up Air is Important

When a facility doesn’t have enough replacement air, it creates a pressure imbalance that leads to a cascade of issues. Negative pressure pulls in unfiltered air through every available gap, bringing in dust, humidity, and contaminants. Exhaust systems may struggle to remove fumes effectively. HVAC systems work harder to compensate, increasing strain on equipment and driving up energy costs.

Beyond operational inefficiencies, poor ventilation can affect employees and customers. Berkeley Lab studies show that improving ventilation rates can decrease employee sick days by up to 35%—a major consideration for businesses prioritizing productivity and occupant well-being.

For a hotel or office building, poor ventilation can lead to complaints about lingering odors, stuffy rooms, or even headaches among staff and guests. In industrial settings, it can mean prolonged exposure to airborne contaminants that affect worker performance and retention.

A make-up air unit addresses these challenges by actively replacing lost air with conditioned, filtered air. The benefits include:

• Balanced indoor air pressure to prevent issues like slamming doors, poor exhaust performance, and uncontrolled airflow. For example, unbalanced air pressure in restaurants or food processing facilities can cause grease-laden vapors to spread into dining areas instead of being efficiently captured by exhaust hoods.
• Improved indoor air quality by replacing stale or contaminated air, reducing odors, dust, and airborne pollutants. In automotive repair shops or industrial plants, this prevents harmful fumes from accumulating and improves overall safety for workers.
• Increased HVAC efficiency, preventing systems from overworking to compensate for air loss. This translates to lower cooling and heating costs year-round for facility managers in high-traffic buildings like shopping malls.
• Compliance with ventilation codes, which require sufficient air exchange to maintain safe and healthy indoor environments. Failure to meet local regulations can lead to fines or, in worst-case scenarios, forced shutdowns.

A properly installed make-up air system is a proactive investment in air quality, energy savings, and overall building performance.

For property owners managing multi-tenant commercial spaces, the right ventilation strategy can mean the difference between satisfied long-term tenants and costly turnover due to ongoing air quality complaints.

In the next section, we’ll explore the different types of make-up air units available and how to determine the best fit for your facility.

Types of Make-Up Air Systems

Not all make-up air systems are built the same. The right system for your facility depends on factors like:

• Air volume requirements
• Energy efficiency goals
• Industry-specific ventilation needs

Below are four common types of make-up air units, each designed for specific applications.

Direct-Fired Make-Up Air Units

Best for: High-volume air replacement in warehouses, manufacturing plants, and distribution centers.

Direct-fired make-up air units are one of the most efficient solutions for quickly replacing large amounts of exhausted air. These systems burn natural gas or propane directly to heat incoming air, ensuring a nearly 100% thermal efficiency rate — meaning nearly all the heat produced goes straight into warming the replacement air.

Where it works best:

• Large warehouses with dock doors that open frequently, causing air loss.
• Manufacturing plants with high exhaust requirements due to heat, fumes, or chemical byproducts.
• Distribution centers, where airflow must be controlled to prevent outside contaminants from affecting inventory storage conditions.

While highly efficient for heating, these systems require proper ventilation planning to prevent indoor humidity imbalances, especially in colder climates.

Indirect-Fired Make-Up Air Units

Best for: Applications requiring precise temperature control, such as office buildings, hospitals, and commercial spaces.

Unlike direct-fired systems, indirect-fired make-up air units use a heat exchanger, preventing direct exposure to combustion gases. This makes them ideal for environments where temperature stability and air purity are essential.

Where it works best:

• Healthcare facilities, where maintaining clean air without combustion byproducts is critical.
• Office buildings, where employee comfort and consistent temperatures impact productivity.
• Retail spaces with customer-heavy areas that need evenly distributed airflow.

Though slightly less energy-efficient than direct-fired units, these systems offer better air quality control, making them a top choice for businesses prioritizing occupant comfort.

Fan-Powered Make-Up Air Systems

Best for: High-traffic buildings supplementing existing HVAC and exhaust systems.

Fan-powered make-up air units work alongside existing HVAC and exhaust systems to maintain consistent airflow. Rather than heating or cooling replacement air, these systems rely on fans to move fresh outdoor air into the building, reducing the strain on existing ventilation.

Where it works best:

• Fitness centers, especially those with pools or saunas, where moisture control is essential.
• Schools and universities, where packed classrooms require a steady supply of fresh air.
• Retail spaces, ensuring stable temperatures while minimizing drafts at frequently used entrances.

These systems are often used in milder climates where heating or cooling the replacement air isn’t as critical, but maintaining proper ventilation is a priority.

Filtered Make-Up Air Systems

Best for: Hospitals, clean rooms, food processing plants, and environments requiring high air purity.

Filtered make-up air units remove contaminants before outside air enters the facility. This makes them essential for industries where air quality directly impacts health, safety, or production processes.

Where it works best:

• Hospitals and healthcare facilities, preventing airborne bacteria and contaminants from affecting patient recovery.
• Food processing plants, where unfiltered air can introduce harmful bacteria or mold spores into the production line.
• Clean rooms and laboratories, where even microscopic particles can compromise research, product development, or pharmaceutical production.

These units can incorporate HEPA or activated carbon filters to capture fine particulates, chemicals, and odors, ensuring a controlled indoor environment.

Signs Your Building Needs a Make-Up Air System

Poor ventilation isn’t always obvious — until it becomes a costly problem. Whether it’s unexplained temperature fluctuations, high energy bills, or complaints from employees and tenants, airflow issues can directly impact your bottom line.

In fact, poor indoor air quality costs businesses over $2 billion annually due to lost productivity and asthma-related absences.

If your facility experiences any of the following signs, it may be time to consider a make-up air unit to restore proper ventilation and efficiency.

Doors That Are Hard to Open or Close

When air pressure inside a building isn’t properly balanced, it creates resistance that makes doors feel unusually heavy or light. Employees might struggle to push open entrance doors, or they might slam shut unexpectedly. This is especially common in:

• Restaurant kitchens, where exhaust hoods pull out large volumes of air without replacement.
• Manufacturing facilities, where process exhaust fans remove air at high rates.
• Large commercial buildings, where high-traffic doorways experience pressure swings.

If doors aren’t opening and closing normally, your building likely has an air pressure imbalance that a make-up air unit could resolve.

Poor Indoor Air Quality – Lingering Odors and Excessive Dust

Many commercial buildings struggle with air quality challenges, with pollutant levels indoors measuring 2 to 5 times higher than outdoor air (RMI). Without proper ventilation, airborne contaminants accumulate, affecting employee health, equipment performance, and regulatory compliance.

If odors linger long after their source is gone or dust accumulates faster than usual, your building probably lacks sufficient fresh air exchange. Inadequate ventilation allows airborne pollutants to build up instead of being properly exhausted and replaced.

• Gyms and fitness centers may suffer from stale, sweat-laden air that deters customers.
• Restaurants and commercial kitchens struggle with grease, smoke, and food odors clinging to walls and furniture.
• Industrial facilities face dust and airborne particles affecting air quality and compliance with OSHA standards.

Without a make-up air unit, these contaminants recirculate and accumulate, making your facility uncomfortable — and potentially hazardous.

Drafts and Uncomfortable Temperature Fluctuations

Do some areas of your building feel too cold, too hot, or constantly drafty? Uneven airflow often points to ventilation imbalances that disrupt temperature consistency and energy efficiency.

• Hotels and mixed-use spaces may experience varying temperatures between floors and rooms.
• Office buildings with fluctuating airflow may cause discomfort for employees, reducing productivity.
• Retail stores with large storefront windows and entrances may struggle to maintain a stable indoor climate.

A make-up air system helps regulate airflow, preventing cold drafts and hot spots from making certain areas uncomfortable while others remain stagnant.

HVAC Inefficiency: High Energy Bills & Performance Issues

When your HVAC system has to work harder to compensate for missing air, energy costs are guaranteed to rise. HVAC inefficiency leads to:

• Higher utility bills, as your system runs longer and consumes more energy.
• Frequent breakdowns, since equipment is overworked to maintain airflow.
• Shorter HVAC lifespan, as excessive cycling wears out components faster.

Implementing energy-efficient HVAC solutions, including make-up air systems, can reduce energy consumption by 20-30%. By restoring airflow balance, make-up air units help HVAC systems operate more efficiently, saving thousands in energy costs annually.

Occupant Complaints About Poor Ventilation

Tenant and employee feedback is often the first indicator of a ventilation issue. If you’re getting complaints about:

• Stuffiness or a lack of fresh air, especially in conference rooms or enclosed spaces.
• Headaches, dizziness, or fatigue, which may stem from poor indoor air quality.
• Mold, condensation, or excessive humidity, which suggests air isn’t being properly replaced.

Neglecting these concerns doesn’t just impact comfort. It can lead to tenant dissatisfaction, lease terminations, and even legal liability in commercial properties.

If your facility is experiencing any of these warning signs, a make-up air unit could be the solution.

How Lee Company Solves Ventilation Issues

For over 80 years, Lee Company has helped businesses across Tennessee, Alabama, Kentucky, and Georgia tackle ventilation challenges that impact energy efficiency, compliance, and occupant comfort.

From high-traffic commercial kitchens to large distribution centers, our team specializes in installing custom make-up air solutions that eliminate pressure imbalances, improve indoor air quality, and optimize HVAC performance.

Here’s how we’ve helped businesses like yours:

• Char Restaurant (Nashville, TN): Installed a kitchen make-up air unit, exhaust fans, and a welded carbon steel grease duct to maintain proper ventilation, keeping air clean and temperatures stable for both kitchen staff and diners.
• Ajax Turner (La Vergne, TN): Addressed stagnant air and excessive heat in garage bays by installing a gas-fired make-up air unit and four roof-mounted exhaust fans, improving air circulation for employees.
• 505 Nashville (Nashville, TN): Implemented three make-up air units as part of the central exhaust and ventilation system to ensure balanced airflow across garages, kitchens, and shared spaces.

If your facility is experiencing air pressure issues, high energy costs, or poor ventilation, Lee Company’s licensed technicians are ready to help! Contact us today for a custom ventilation assessment tailored to your building’s needs.