How to Choose the Right Workshop Exhaust Fan Size

Why Fan Size Matters More Than You Think

Walk into any busy workshop in midsummer, and you’ll probably feel it — that trapped, heavy air that refuses to move. Machines are humming, people are working, but the heat just builds up.
It’s not just uncomfortable; poor ventilation affects productivity, machinery life, even safety.

The problem often starts with the wrong fan size.
An undersized exhaust fan can’t pull out enough hot air or fumes. Oversized units may waste energy or cause air imbalance.

At DAIHO Ventilation, our engineers see this a lot when helping factories upgrade their systems. Sizing, it turns out, isn’t a guess — it’s engineering.

Air Volume and Ventilation Basics

Before you grab a fan catalog, it helps to understand two simple ideas:

• Airflow (m³/h or CFM): the total amount of air moved per hour.
• ACH (Air Changes per Hour): how many times the full air volume of a room is replaced in one hour.

Different work environments need different ventilation rates. Here’s a quick reference:

Typical Air Change Rates (ACH):

• Light duty workshop: 10–15 ACH
• Medium duty production: 15–25 ACH
• Heavy or heat intensive areas (like welding): 25–40 ACH

If you’re unsure, start in the middle range — then adjust based on temperature or humidity feedback.

How to Calculate the Right Exhaust Fan Size

The basic rule is simple:

Required Air Volume=Room Volume×ACH

Let’s do a quick example.
A small workshop of 120 m² with 4 m ceiling height → 480 m³ of air space.
If you aim for 20 ACH (typical for medium duty operations):

480×20=9,600 m³/h

That’s your minimum airflow requirement.

Now, check available fan sizes. For instance, DAIHO Ventilation’s wall exhaust fans range from 20,000 to 44,500 m³/h, which easily covers workshops from around 100 to over 500 square meters.

If you need more precise control, multiple smaller fans are often better than one large unit — they distribute air more evenly and make maintenance easier.

Wall vs Roof Exhaust Fans: Which One Fits Your Space

Both wall mounted and roof mounted fans have their place. The best choice depends on your building layout, air movement pattern, and maintenance preferences.

Wall Exhaust Fans
Easy to install and service
Ideal for targeted zones (e.g., near machinery or welding lines)
Effective for horizontal air movement

Roof Exhaust Fans
Better for removing rising heat and fumes
Save wall space for equipment or inlets
Support vertical airflow and natural convection

In one of DAIHO Ventilation’s manufacturing projects, combining wall and roof fans increased airflow efficiency by nearly 30%. Sometimes balance — not power — is what you really need.

Key Factors That Influence Fan Sizing

Choosing a fan by room size alone doesn’t tell the full story. Consider these practical details:

• Workshop layout & ceiling height: tall spaces need more airflow to circulate evenly.
• Heat sources: machines, furnaces, or compressors raise the required ACH.
• Type of production: woodworking, metal fabrication, or textile lines each generate different air contaminants.
• Local climate: hot or humid regions may require extra capacity.
• Air inlets: every exhaust fan needs a clear path for fresh air intake.

To keep it simple, here’s a quick checklist:

Measure your space accurately
Balance exhaust and intake openings
Check voltage and motor specs (especially for overseas projects)
Plan for maintenance access
Always match fan speed to target airflow

Common Mistakes to Avoid

Even experienced facility managers make these errors:

1.Sizing only by fan diameter instead of airflow rate — 54″ doesn’t always mean higher performance.

2.Ignoring inlet air balance — exhaust without intake causes pressure loss.

3.Poor installation height — too high, and airflow may never reach work zones.

4.Overlooking voltage compatibility — different countries or machines may use 220V, 380V, or custom setups.

DAIHO Ventilation’s custom voltage options often solve this issue for overseas clients. It’s a small detail that prevents big downtime later.

Practical Tips for Better Workshop Ventilation

A well sized fan works best when supported by smart airflow design.
Here are a few easy wins:

• Pair exhaust fans with louver windows or fresh air inlets on the opposite side.
• Keep shutters and blades clean — dust build up cuts airflow by up to 15%.
• Consider variable speed drives (VSD) for energy efficiency during off peak hours.
• Plan airflow zones around machinery, not just walls

For roof fans, install rain covers or PVC shutters to protect from weather.

Sometimes, even tiny tweaks — such as dropping an inlet just one meter down — can really boost how comfy folks feel inside.

Conclusion: Smarter Ventilation Starts with Proper Sizing

Figuring out the perfect size for your workshop exhaust fan isn’t too tricky, yet it calls for some quick math and a touch of know-how. First, measure up your area. Then, grasp what kind of air flow you truly need. And hey, skip the trap of thinking “bigger must be best every time.”

DAIHO Ventilation offers both wall and roof exhaust setups with adjustable air movement (20,000–44,500 m³/h), tough SMC fiber reinforced blades, and sturdy galvanized casings made for tough factory use.

Getting the size spot-on does way more than just bring in fresh breezes. It keeps workers safer. It helps machines last longer. Plus, it cuts down on power waste big time.

Because, when the air flows just right, the whole workshop runs smoother, too.

FAQ

Q: Why is choosing the correct exhaust fan size important for a workshop?

A too-small fan fails to clear hot air or smoke well. A too-big one burns power. Or it messes air flow. Good sizing ups comfort. It boosts work output. Machines live longer. And safety gets better.

Q: How do I calculate the required airflow for my workshop exhaust fan?

Try this: Required Air Volume = Room Volume × ACH.

Q: What are typical Air Changes per Hour (ACH) rates for different workshops?

• Light duty: 10–15 ACH
• Medium duty production: 15–25 ACH
• Heavy or heat-intensive (e.g., welding): 25–40 ACH

Q: What’s the difference between wall and roof exhaust fans?

Wall ones install quick. Easy to fix too. They push air sideways near tools. Roof fans pull up hot stuff and smoke best. They free wall spots. And help hot air rise natural.

Q: What common mistakes should I avoid when sizing and installing workshop exhaust fans?

Skip judging by size alone—like 54″ ain’t always tops. Balance inlet air. Put ’em at right spot high. Match voltage right. And leave room to fix later.