Industrial Drying Room Design: Getting It Right First Time

A drying room that’s too small can quickly become a bottleneck. Work starts piling up, operators are waiting for space and jobs take longer to get through the finishing process.

But making the room too large creates a different problem. You’re paying to heat a much bigger volume of air than you actually need, every time the room runs.

Getting the size right isn’t simply a case of measuring the largest product and adding some extra space. The drying room needs to work around the products you’re finishing, the coating system you’re using, how quickly your spray operation produces work and how that work moves through the workshop.

Whether you’re running a bodyshop, joinery workshop, metal fabrication business or a larger production operation, the basic principle is the same: design the drying room around the process, rather than trying to fit the process into a standard-sized room.

Start with the coating, not the room size

Before deciding how big the room needs to be, establish what you’re actually trying to dry or cure.

Air-drying paints, waterborne coatings, two-pack systems, powder coatings and specialist industrial finishes can all have very different requirements. Some coatings mainly benefit from warm, moving air. Others need a controlled temperature and a specific bake cycle to achieve their required properties.

The coating manufacturer’s technical data sheet should be your starting point.

Don’t assume that because one coating cures at a particular temperature, another similar-looking product will do the same. Flash-off times, drying temperatures and curing times can vary considerably between products.

Get the technical information for the coatings you intend to use before finalising the heating system, airflow or room size. Otherwise, you risk designing a room around assumptions that may not apply to the actual coating.

The products themselves need looking at too.

Vehicle panels, cabinet doors, fabricated frames and larger steel components all need enough space around them for air to circulate properly. Long sections of steelwork may be easier to handle on an overhead track system rather than moving them around on floor trolleys.

This is particularly useful in joinery and steel workshops where work needs to move from preparation, through spraying and into drying without being handled repeatedly.

For smaller components, drying racks can make better use of the available space. The important point is not simply how many items you can physically fit inside the room. You need to leave enough space for air to reach the coated surfaces.

Pack products too tightly together and you can end up with a room that reaches its target temperature while parts of the coating remain soft.

How big should the room be? Start with your sprayer

One useful way of approaching the size question is to work backwards from your spraying operation.

Think about how much work your sprayer can realistically produce during one drying cycle.

For example, if a coating requires around 30 minutes at temperature, consider how much your operator or robotic system can spray during those 30 minutes. That gives you a much better indication of the amount of work the drying room needs to accommodate than simply choosing a standard room size.

From there, consider your expected production.

If you know you’re going to increase output or introduce larger products, it makes sense to allow for that during the initial design. Adding a little flexibility to the layout can be worthwhile.

What you don’t want to do is build a room several times larger than today’s operation simply because you might need it one day.

Oversizing is easy to do because extra space sounds useful. The problem is that you don’t just pay for the extra panels and construction. You also have a larger volume of air to heat every time the room operates.

In many cases, it makes more sense to leave room for additional racking or an extension to the handling system rather than heating a large empty volume from day one.

Think about access: first in isn’t always first out

This is an easy part of the design to overlook.

The first product you put into the drying room isn’t necessarily going to be the first product you need to remove.

Different coatings and products can have different drying times. You may need to get to something at the back of the room while newer work is still sitting closer to the entrance.

That means the layout needs to be considered as carefully as the overall dimensions.

Make sure operators can get to individual products without having to move several other items first. Leave proper walkways where they’re needed and think about how products are loaded and unloaded throughout a normal working day.

This becomes particularly important with racks and overhead tracks. A layout that looks efficient on a drawing can be frustrating to use if operators have to squeeze around wet work or move several finished items just to reach one product.

The drying room needs to work as part of the production process, not as an isolated box.

Airflow matters more than most people think

Getting the room up to temperature is only part of the job.

The heated air needs to reach the products, move around them and remove moisture or vapour where appropriate. At the same time, the air movement shouldn’t interfere with a coating that is still settling or flashing off.

The amount of airflow required will depend on the process, the coatings being used and how the room is intended to operate. A drying room, curing oven and ventilated holding area aren’t necessarily going to have the same requirements.

Poor airflow often shows itself through inconsistent results.

You might find that products near one part of the room dry faster than those elsewhere. Corners can be slower, surfaces can remain soft and the front of a load can behave differently from the back.

Dust can also become a problem if air is being pulled through the room in an uncontrolled way.

This is why supply and extract positions should be considered around the actual load. Simply putting ductwork wherever it is easiest to install can produce an uneven result.

Duct size, grilles, baffles and the position of the air outlets all influence how the air travels through the room.

There’s also a balance to be found with air velocity.

Too much air movement can increase energy use and potentially interfere with a coating that hasn’t finished flashing off. Too little movement can leave moisture or vapour around the work and slow the drying process.

With waterborne coatings in particular, air movement can be an important part of the drying process.

It can also be useful to think about the drying cycle in stages rather than treating it as one fixed condition. Flash-off, drying, curing and cooling may each require different conditions depending on the coating being used.

Fresh air, extraction and pressure

A drying room may use fresh, filtered and heated air while extracting air from the room to maintain the required conditions.

Exactly how that system should be arranged depends on the process and the site.

If flammable solvents or vapours may be present, ventilation and equipment selection need to be considered as part of the wider fire-safety and hazardous-area assessment.

You also don’t want the room simply drawing unfiltered workshop air through gaps around doors, panels or service penetrations. That can introduce dust and make temperature control more difficult.

At the other extreme, excessive positive pressure can make doors harder to open and force air into surrounding areas.

The objective is controlled airflow rather than simply moving as much air as possible.

Filtration is another part of the system that is easy to overlook during the initial design. Filters protect the process and the equipment, but they also need to be practical to maintain.

Think about where the filters are located, how they will be accessed and how often they are likely to need changing. A filter that requires half a day of dismantling to reach is unlikely to be changed as regularly as one that can be accessed quickly.

If you’re planning the spraying and drying areas together, it’s worth considering how the dry filter spray rooms and drying stage will work alongside each other.

Heating: size it for how you really work

Heating requirements aren’t determined by floor area alone.

The calculation needs to consider the room volume, insulation, incoming air temperature, target process temperature, extraction and heat losses through the structure and doors.

The larger the room, the more air there is to heat. That’s one reason unnecessary room volume can become expensive over time.

Doors can have a surprisingly large effect too. A large door opening repeatedly during a shift can allow a significant amount of heated air to escape and increase the time needed for the room to recover.

The heating system itself can take several forms.

Gas-fired, electric and indirect-fired systems can all be suitable depending on the application. The choice will depend on factors such as available utilities, required temperature, operating hours, energy costs and the cleanliness requirements of the process.

Where combustion products need to be kept away from the process air, an indirect system may be appropriate.

Adding heat to an existing room

Not every business needs to build a new drying room.

If you already have a suitable room or bay and simply need to introduce additional heat, a mobile infrared heater can be an option.

It can be used in insulated and non-insulated spaces, so it doesn’t necessarily require major alterations to the building.

It can also be useful where electrical capacity is limited. Some sites don’t have enough spare electrical capacity for a new electric heating system, while others don’t want to undertake an electrical upgrade.

A mobile infrared heater uses LPG gas bottles and doesn’t require a mains electrical connection for the heating itself, making it a self-contained option.

However, infrared isn’t automatically the right answer for every product.

The shape and material of the items being dried can affect how well infrared heating works. Consider the product geometry and the coating process before choosing this approach.

If you’re starting from scratch, a purpose-built drying room gives you the opportunity to design the insulation, heating and airflow as one system rather than trying to make separate components work together afterwards.

Controls and insulation

Controls should be straightforward enough for operators to use without unnecessary complication, but they still need to provide the functions required by the process.

Depending on the application, this might include temperature set points, timed programmes, fan control, alarms and safe shutdown functions.

Some processes may also benefit from staged cycles, such as a lower-temperature flash-off period followed by a higher-temperature curing stage.

Temperature sensors should be positioned with the process in mind. Measuring the temperature close to the heater doesn’t necessarily tell you what is happening where the products are actually sitting.

Insulation is another area where trying to save money at the start can prove expensive later.

Insulated panels, properly fitted doors and sealed service penetrations all reduce heat loss. That means the heating system doesn’t have to work as hard to maintain the required conditions.

A cheaper panel specification can look attractive on the initial quotation, but the difference can come back through higher running costs over the life of the room.

Plan loading, doors and the rest of the workshop

A drying room doesn’t operate on its own.

It sits between other stages of the finishing process, so the way products arrive at the room and leave it needs to be considered from the beginning.

If products are going to arrive by forklift, trolley or overhead track, allow enough room for the equipment as well as the product.

Consider turning circles, clear door openings, track height and safe access for operators.

Door selection is also worth thinking about.

A standard personnel door may be perfectly adequate for smaller work. Larger products may require bi-fold, sliding or powered doors, particularly if they’re being moved in and out frequently.

The clear opening needs to accommodate the largest load you actually intend to move through the room. That includes the trolley, rack or handling frame — not just the coated component itself.

Lighting is another practical detail.

Operators need to be able to inspect the finish, load the room safely and clean it properly. Lighting should be positioned so that racking and hanging products don’t create large areas of shadow.

Maintenance access should be planned at the same time.

Fans, heaters, burners, control panels, filters, ductwork and access doors all require space. Equipment that looks neatly packed together on a drawing can become difficult and expensive to service if there isn’t enough room around it.

Build safety in from day one

A drying room can involve high temperatures, moving loads, electrical equipment, flammable materials and solvent vapours.

The safety requirements depend on the products being used and how the room operates, which is why a site-specific risk assessment is important.

Where coatings or cleaning products can create an explosive atmosphere, hazardous-area considerations need to be addressed as part of the design. LPG storage and use also need to be considered where applicable.

In the UK, a drying room design may need to take account of requirements and guidance relating to DSEAR, fire safety, electrical installations, ventilation and building control.

Exactly what applies will depend on the site and process, so these issues should be raised early with the equipment supplier, responsible person and any relevant specialists or authorities.

Some of the most useful safety measures are also fairly straightforward.

Emergency stops should be accessible. Controls should be clearly identified. Cable routes should be protected, cleaning access should be safe and operators should have clear procedures for loading and unloading.

If staff have to work out their own way of safely using the room, the design hasn’t gone far enough.

Questions to answer before you install

Before approving a drying room design, make sure you have clear answers to the basics.

What is the largest product?

What is the maximum batch weight?

What coating system are you using?

How much work can your spraying operation produce during one drying cycle?

What temperature and cure schedule does the coating manufacturer specify?

Then look at the building.

Check your available electrical and gas supplies, ceiling height, access routes, ductwork route and external discharge position. If you’re using an overhead handling system, make sure the building structure and proposed support arrangement are suitable for it.

It is also worth thinking about the less obvious jobs.

How will the room be cleaned? Who will change the filters? Where will waste go? How often will the doors be opened? How will products be loaded when production is busy?

And then consider growth.

There’s nothing wrong with designing for increased production, but there’s a difference between allowing sensible room for expansion and building a room around a production level that may never happen.

A drying room should be large enough for the work you actually need to process, with sensible provision for what you reasonably expect to add later.

Getting the drying room right

A good drying room should make the finishing process easier, not create another problem for operators to work around.

The starting point isn’t the room itself. It’s the work going through it.

Look at the products, coatings, production rate, drying cycle and handling method first. From there, the room size, heating, airflow, filtration, doors, insulation and controls can all be designed around the actual process.

That approach generally gives you a room that is easier to operate and maintain, without paying to heat space you don’t need.

If you’re considering a new drying room or modifying an existing space, the important thing is to work through the process before choosing the equipment. The right specification will depend on what you’re drying, how much you’re producing and how the room needs to fit into the rest of your workshop.