Are Your Exhaust Fans Really Keeping You Safe?

Most engineers and facility managers assume that if an exhaust fan is sized correctly, the problem is solved. But here’s the hard truth: if your exhaust plume doesn’t rise high enough above the roofline, you could be sending hazardous, corrosive, or odorous fumes right back into your building.

That means:

• Risk of re-entrainment into air intakes
• Accelerated corrosion of building structure
• Potential code compliance issues with local authorities
• Increased liability for both designers and owners

The question is simple: how do you prove your system has adequate fume dispersion?

Introducing Our New Plume Height Calculator

At Plastec Ventilation, we’ve built a free, easy-to-use online tool that calculates the plume height of your exhaust system based on:

• Airflow (CFM / L/s)
• Fan model and discharge diameter
• Stack height and configuration

With just a few inputs, you’ll instantly know whether your design meets dispersion requirements and keeps harmful exhaust away from sensitive re-entry points.

No more guesswork. No more “hoping” your plume meets compliance standards.

Backed by Industry Standards

This isn’t just theory. Multiple standards and organizations have long emphasized the importance of plume rise and exit velocity:

• ANSI/ASSP Z9.5 – Laboratory Ventilation: Recommends a minimum 3,000 fpm exit velocity to prevent “stack-tip downwash,” where exhaust is pulled back toward the roof.
• ASHRAE Laboratory Design Guide: Provides equations and methods for calculating plume rise, with typical recommendations of 2,000–3,000 fpm exit velocity.
• NFPA 45 – Fire Protection for Laboratories Using Chemicals: Primarily focused on fire safety, but also includes exhaust design requirements to prevent vapor buildup.

All of these standards point to the same outcome: keep hazardous fumes away from the building envelope and air intakes.

Our calculator takes these principles and applies them directly to your fan and stack configuration—helping you design with confidence, meet code requirements, and protect both people and property.

Why This Matters

Whether you’re designing for a lab, wastewater plant, natatorium, or chemical storage facility, proving compliance is more important than ever.

Our polypropylene exhaust fans are already trusted for their corrosion resistance. Now, with our plume height calculator, we’re helping engineers take the next step—protecting people, buildings, and compliance from day one.

👉 Try the tool today on our website and see how your next design measures up.

https://www.plastecventilation.com/pages/plume-height-calculator