Cross draft vs Downdraft vs Side Downdraft Paint Booths

ten get asked whether or not a customer should use a cross draft or downdraft spray booth. I also often get asked what size booth they should use. The goal of this article is to cover the main styles of spray booths, the benefits, and drawbacks of each style booth, and how much space you may want in a spray booth based on your product size

Cross draft Spray Booths

Cross draft spray Booths bring air through the front of the spray booth and exhaust it out at the rear of the spray booth. The major benefits to this type of booth is that they are more affordable then downdraft booths and typically easier to install because you do not have any concrete work to be performed. When accompanied with an air make up unit they are often as effective as a downdraft spray booth in providing a clean finish. The downside is that if your top priority is finish quality a downdraft will always be a cleaner paint finish because all overspray is pulled down away from the product while in a cross draft spray booth overspray at the front of the spray booth can potentially land on your product at the back of the booth.

Downdraft Spray Booths

Downdraft spray booths bring air in through the ceiling and down through the floor into an exhaust chamber which is exhausted at the rear of the paint booth. Downdraft spray booths will provide the cleanest possible finish. It is what is used in high end auto body facilities due to the clean finish provided. The downside to downdraft booths is that they typically require a raised floor or concrete pit which can be an additional expense. If you plan the concrete floor prior to purchasing your paint booth you can install a downdraft booth at the same cost as a cross draft paint booth. Additionally, with very large objects downdraft booths do not make sense because air removed is based on the length and width of the paint booth making it harder to reorient your product to reduce air removed from the building.

Side Downdraft Paint Booths

Side Downdraft paint booths bring air in through the roof and exhaust it out the sidewalls of the paint booth. This allows for a downdraft finish quality but doesn’t require a concrete pit. It might seem like a Side Downdraft paint booth is all the benefits of the downdraft without any drawbacks (concrete work ect), but there are some negatives to a Side Downdraft paint booth. First is that it will require a lot of ductwork which can often lead to a cost similar or even more expensive than a downdraft paint booth. For example, a Side Downdraft paint booth will require at least twice the number of duct runs that a comparable cross or down draft paint booth will need with longer booths even more duct runs may be needed. Each duct runs also adds an additional hole in your roof which can be a source for water leakage over the long term. An additional downside to Side Downdraft spray booths is that overspray from painting is carried back against the painter which can be annoying for some painters. A final consideration is that a Side Downdraft will exhaust a similar volume of air as a downdraft paint booth. Ultimately, f you absolutely need a downdraft finish and are limited on altering the floor of a building a Side Downdraft can be a good solution. It can also be a great solution for a smaller booth where only two duct runs would be needed and no floor alterations can be made (such as a small auto body shop).

• Ultimately if your choosing between a cross draft and downdraft paint booth consider the following.  If you need the finest finish possible consider the downdraft.  If your on a budget or do not want to alter your floor consider the cross draft paint booth.

What size Paint Booth Do I need?

The size of paint booth you will need depends primarily on the size of your product. If you are buying a cross draft paint booth try to keep the width and height of the booth to the minimum you need by orienting your parts so they face deep but not wide in relation to the booth opening. The reason to keep the face opening small is that the amount of air you remove or if using a pressurized spray booth the amount you have to replace with a cross draft spray booth is determined by the size of the width and height of the face opening. A larger opening will create extra negative pressure and even remove all the heat from your building vary fast depending on your buildings size. So if your product is 45 feet x 3 feet by 8 feet you would want to consider a booth that is only about 12 feet wide but very long. As a general rule of thumb you want to keep about 3 – 5 feet of space on all sides of your product for maneuverability so in the product mentioned above you would want about a 52 foot deep booth. Additionally, always try to ask for factory standard sizes so that you select a paint booth that is not custom designed, typically booths will come in varieties of 3 foot lengths but always make sure to ask for a standard size unless it will not work for your specific situation.

Air Make Ups and Cure Capabilities

As we have discussed paint booths will remove a lot of air from your building and depending on the size of the booth and your building you may completely empty your building of all temperate air in minutes. If this is your scenario it can be important to replace the air your spray booth is removing. You also have to consider whether you want to add a cure capability to your spray booth. For reference sake air make up units are a large expense but cure capabilities are not that much extra cost wise. The cure capability will allow you to raise a booth to about 160 degrees and bake the coating reducing product dry time by up to 50%.  If you have a small shop or large paint booth or need the ability to turn product completely, or are worried about paint odor from a drying product impacting your facility, then an air make up unit can be a great idea.

• Consider an air make up for your paint booth if you have a large paint booth, a small shop, or if you want to be able to accelerate product dry time significantly.

Photo credit:

By Sebog6 (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons