Kitchen exhaust design can be challenging. Engineers must determine how much air needs to be exhausted, where the system can terminate and how to prevent cooking smoke and odours from affecting neighbouring properties—or the restaurant itself.

On this project, Evolve Mechanical Solutions was retained to investigate a kitchen exhaust system that was making part of the restaurant nearly unusable.

The Problem

The kitchen exhaust terminated directly above an outdoor patio. Its discharge blades were pointed downward, directing cooking smoke and odours toward the customers seated below.

Patrons understandably did not want to sit there. The restaurant was effectively losing valuable seating—and revenue—because of a mechanical design problem.

Worse yet, some of the discharged air was being drawn back into the building, carrying cooking odours into the dining area.

Would You Sit Under This?

Watch how one kitchen-exhaust mistake sent smoke and odours toward customers—and turned valuable patio seating into dead space.

What the Code Requires

NFPA 96, Standard for Ventilation Control and Fire Protection of Commercial Cooking Operations, states:

7.8.3(4): The exhaust flow directed perpendicularly outward from the wall face or upward.

 

In Vancouver, the engineer must also complete the City of Vancouver K2 Kitchen Ventilation Details Checklist. Item 3(e) requires the engineer to confirm:

Item 3(e): For a wall termination, the exhaust flow is directed upward or perpendicularly outward from the wall face. [7.8.3(4)]

These requirements are fundamental to commercial kitchen exhaust design. If they had been followed during the original design and installation, the problem likely would have been avoided.

The First Correction

We changed the orientation of the discharge blades from downward-facing to upward-facing, directing the exhaust away from the patio.

This prevented smoke and cooking odours from being blown directly onto customers and helped restore the patio as comfortable, revenue-producing seating.

However, that was only part of the problem.

The Hidden Problem: Building Pressurization

Our investigation also found that the kitchen was exhausting substantially more air than the make-up air system was replacing.

This created severe negative pressure inside the restaurant.

Common symptoms of excessive negative pressure include:

  • Exterior doors that are difficult to open
  • Cold drafts around doors and windows
  • Poor kitchen hood capture and containment
  • Uncomfortable indoor temperatures
  • Cooking smoke and odours being drawn into dining areas
  • Reduced kitchen exhaust performance

The existing make-up air system was delivering only approximately 40% of the kitchen exhaust airflow. This imbalance created drafts, made exterior doors difficult to open and contributed to smoke and odours entering the dining area.

Fortunately, the existing make-up air fan had enough potential capacity to meet the restaurant’s needs.

After reviewing the equipment, we adjusted the fan’s pulley ratio and upgraded the motor to increase the delivered make-up airflow. The system then required proper testing and balancing to confirm that the kitchen exhaust and make-up air were operating together as intended.

The Lesson

A kitchen exhaust system is not simply a fan connected to a duct. Its discharge location, exhaust airflow, make-up air and effect on building pressure must all be considered as one coordinated system.

A poorly designed termination can make a patio unusable. An unbalanced ventilation system can create drafts, reduce exhaust performance and pull cooking smoke and odours back into the restaurant.

These problems do more than create discomfort—they directly affect the customer experience and can cost a restaurant valuable revenue.

A proper mechanical review during design, installation and commissioning can prevent these expensive problems before opening day.

James Hicks, P.Eng.
Principal
Evolve Mechanical Solutions Inc.
236-777-3487
www.evolvesolutions.ca

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