Heated Makeup Air for Spray Booths

Reasons to heat makeup air and ways to accomplish it. November 15, 2011

Can someone help me understand an air make-up system? They are heaters that warm your booth? I can't imagine the amount of heat it would take to heat a booth while a 24" exhaust sucks it out as fast as it is made. I was just looking at a 10 x 12 booth on the Machinery Exchange which has an air make-up with it. These must cost a fortune to run.

Forum Responses
(Finishing Forum)
From contributor C:
Yes, they are designed to balance airflow. Without make up air, your exhaust fan will scavenge air from wherever it can, often bringing cold and dirty air to your booth. Especially in cold climates, they are essential. They bring outside air and can raise the temp to 80 F or more. Often the heaters are rated at 1,000,000 BTU so yes, they use a lot of gas.

From contributor A:
We put in an air make up a little over a year ago. It replaces the 8000 cubic feet of air our spray booth removes. Our spay booth is a non-pressurized car booth, meaning the air from the air make up is dumped in front of the filters outside the intake end of the booth. We are in Canada, so our winter heating requirements are significant. Our heater is about 970,000 BTU and can raise the air temperature by a maximum of 90 degrees F. So if it is -20F outside, it will produce 8000 feet of 70F air. The heater runs continuously but varies the intensity of the flame to suit the amount of heat required (I'm not a heating guy; this is how it was explained to me). Meaning we aren't sucking the full BTUs most of the time, thankfully.

After having it for 1 1/2 winters, I would say that it is worth the expense. We paid about $33,000 which also bought us a new stack for the booth. Both the heater and stack were new and installed for that price. The improvement in our finishes has been wonderful and the working conditions for the rest of the shop are also great. We used to have to roll up the garage doors about 8" to allow air in when the fan was on.

The heating cost year over year definitely went up, but not as much as you may think. My gas bill was up by about 20%, $1500. You have to remember that if you are running your fan without an air make up, you are still sucking your heat out. All the air make up does is keep things at a decent temperature, perhaps 15-20 degrees warmer.

From contributor E:

I put in a 5000 cfm heated air makeup unit about 3 years ago. I am absolutely happy. I agree that the gas usage does not go up as much as you would think. When I am done spraying, the temperature is 70 degrees, and I do not have all this time that the heaters are running to recoup the temperature.

Make sure that your air makeup unit is set at about 100 cfm higher than your exhaust system. This helps to eliminate air swirls and it also gives you a little bit of out pressure when you open a door, thus preventing dusty shop air from entering the booth. You can do this because most air makeup units have squirrel cage fans.