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Why you won’t find a variable frequency drive (VFD) on our unheated booths

We have many customers that ask us if we offer a variable frequency drive or VFD for our paint booths. The answer is simply “No” and we have a very good reason on why.

A variable frequency drive allows you to control the speed of a motor. It is also known to be called a variable speed drive, adjustable speed drive or an adjustable frequency drive. We are very familiar with the VFD because we utilize them on our Air Makeup Units (which controls the exhaust fan on our heated booths – but not the intake fan). The difference is when we control the exhaust fan on the AMU’s, your booth remains in compliance and safe to use.

The VFD can turn the speed of the motor up or down depending on the motors capabilities. Most customer’s request this so they can reduce the speed of the motor for several applications explained, but not fully known to us as a manufacturer.

The simple answer, “No”, is followed by an explanation that if you turn down the motors speed; the booth will not be in compliance with the code requirements. A certain amount of airflow is required to meet the NFPA-33 guidelines.

To explain it a little more clearly, here is what our engineer Tracy Beach has said about this subject:

Insufficient airflow:

* will lead to poor painting quality

* will cause excessive fumes

* may easily lead to a fire or explosion due to flammable fumes not being exhausted from the spray booth. This is not a matter of convenience; the spray booth must be properly exhausted or it is simply a box holding lights and explosive fumes. The ventilation performance of most spray booths designed by Standard Tools is 6-10% above the NFPA-33 and OSHA code requirements.  Decreasing the airflow would be dangerous and may result in poor coating quality since the over spray would not move away from coated surfaces.

We urge our customer’s to contact the local authorities and find out what their cities requirements are prior to making a purchase of our paint booth. Whether it is the building department or fire marshal, we want them to be aware of the requirements. We also offer a paint booth permitting guide to help them along in the process.

Please contact us with any questions or concerns you may have. We are here to help guide you in the decision making process.


During spray jobs in a paint booth, the exhaust system must draw substantial quantities of air out of the shop in order to operate. These volumes must be replenished with equal volumes of air coming into the booth.

STE_AMU Full CornerAIR MAKE-UP (AMU) is defined as…a mechanical means of replacing air that has been exhausted out of the booth.

It’s simple…. it’s all about paint booth air flow. How much air in being put into the booth and how much is being taken out. Airflow while spraying takes the over-spray away from the paint job and out of the booth.

Air in – Air out. Air in – Air out. Air in – Air out. Air in – Air out. That’s it. With the Sure-Cure Air Makeup Unit, you control the amount of air pushed into your booth. Why would you need to push air into your booth?

When the exhaust fan of the booth is turned on, it creates a “negative” air pressure in the booth cabin (taking out more air than is being put in). When there is a negative air pressure, the booth will try to suck in as much air as possible, including dirt and debris from outside the booth. THINK VACUUM CLEANERS.

To counter this “negative” pressure, an Air Makeup Unit (AMU) unit is used to supply air to replace the air being exhausted. If the AMU is designed to force more air into the booth than is exhausted…the booth is said to have “positive” air pressure. In this case, the booth has more air than outside the booth and when a door is opened, dirt and debris is pushed away from the booth. THINK STANDING IN FRONT OF A FAN. Continue reading PAINT BOOTH AIR FLOW: HOW IT WORKS

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