Obtaining a pottery kiln can be a tough task, especially if you’re working off a budget.
But are you aware of the safety factors involved in firing pottery? Specifically, does your kiln have a vent installed on it?
Pottery vents are critical when it comes to firing a kiln within closed living spaces. Even if this space receives a cross breeze, a pottery kiln vent ensures the gases coming off the kiln are safely removed from your workspace in order to provide a healthy environment.
At the same time, pottery kiln vents also provide a number of non-health-related benefits. These may include more vibrant pottery glaze results, a kiln that cools down faster, and an extended life cycle for particular internal kiln components.
Keep reading if you’re not quite convinced you need a pottery kiln vent. We’ve got all the information you need to make a smart decision about this important safety component of a pottery kiln.
What’s the Purpose of Venting a Ceramic/Pottery Kiln?
There are many reasons you might vent your pottery kiln. Each of them serves to improve your overall experience. Below is a quick summary of some of the benefits of venting your ceramic kiln.
Venting your pottery kiln will:
- Create a safer working environment for you and anyone else around you, and the kiln
- Remove odors and toxic gases, such as carbon monoxide, from both within the kiln as well as the surrounding working space via an exhaust system
- Prolong kiln elements, such as the thermocouple
- Improve your bisque firing and glazing results
- Allow you to cool the kiln down rapidly but in a controlled manner
It’s a common misconception that venting the toxic gases from your kiln pollutes the air outside. However, those gases mix with what’s already in the atmosphere and disperse, diluting any toxicity as the air dissipates. The gases cease to be a health hazard once they hit the outside air.
Do You Need to Vent a Pottery Kiln?
It’s proper safety practice to vent your pottery kiln. While using your kiln in an open, well-ventilated space can work temporarily in place of a vent, there’s only so much a natural cross breeze can do to dilute the chemicals coming from the kiln as it fires. Removing fumes from your workspace is critical to your health.
For example, many kilns burn off organic materials from the clay body and glazes, which produce gases such as carbon monoxide, sulfur oxides, hydrogen fluoride, as well as metal vapors, depending on what you’re firing.
Containing these gases within a space that also includes you or other crafters can cause serious health issues.
At the same time, improperly vented kilns do not produce quality glaze firings. In fact, if you’ve noticed your kiln is full of fired pieces that are dull and/or weak in color, this could be due to a lack of air circulation in the kiln.
Installing an exhaust system could allow the glazes the oxygen necessary to produce better results. Even though the flexible hose directs fumes and heats away from the kiln, it’s all about the airflow over the pieces within the kiln. The kiln continues to produce heat, while the fumes and odors are pulled from the clay and sent to another location.
Other common symptoms include glaze color migration and gray inner areas on any pieces you’ve fired. Basically, the glaze doesn’t have a chance to breathe as well as it should in order to produce the vibrant, deep colors typically associated with pottery glaze.
How Much Ventilation Does a Kiln Need For Proper Kiln Venting?
When it comes to venting your kiln, having more ventilation than necessary isn’t quite a bad thing. In fact, it can help clear out your workspace with more efficiency if that’s the case.
To calculate how much ventilation your kiln needs, use the following formula:
BTU per hour / (1.085 x Delta T) = CFM
Most kilns will come with a specification of how many BTUs, or British Thermal Units, they put out per hour. You can easily find this number in your owner’s manual or directly contact the manufacturer.
A temperature differential determines the Delta T in this equation. Take the highest temperature you want your kiln room to be (let’s say 120 degrees Fahrenheit) and the highest temperature you want to fire in (let’s say 90 degrees Fahrenheit) and subtract the second from the first. The remainder (30 degrees Fahrenheit) is your temperature differential or Delta T.
The end result, or cubic feet per minute (CFM), will determine how powerful the fan needs to be in order to vent your kiln room properly. Be aware that you will also need a way to makeup air if you plan to put a kiln vent in, as you’ll need to replace the air pulled out.
Types of Kiln Ventilation You Need for a Kiln
There are two main types of kiln vents you’ll come across in your search: updraft and downdraft. You may have also heard these types called vent hoods (updrafts) and negative pressure systems (downdraft). Each of these types has its own pros and cons, but downdraft is most common. We’ll start with that one first.
Downdraft Kiln Vent
Downdraft kilns are often referred to as negative pressure systems because of the way air flows from the kiln out to the ambient air. Since the blower fan removes air from the kiln room, it creates a negative pressure that fresh air must be filled in. This is why it’s important to have a fresh air source if you plan on using a downdraft kiln vent exhaust system.
Installing a downdraft kiln vent is simple in terms of process. Holes are drilled in the top and bottom of the kiln to allow for airflow through the kiln itself.
Then, a bypass or collector cup is installed at the bottom of the kiln. This piece attaches to ductwork or a flexible hose leading to the fan and into the ambient air.
The ducting on a downdraft kiln vent can be made from galvanized steel dryer ducting, aluminum, or PVC. Because the fan moves air independent of the airflow, there’s a constant speed that better removes toxic gases from the kiln room.
Compared to updraft kiln vents, downdraft kiln vents are better at removing a larger portion of gases from the kiln room.
Updraft Kiln Vent
Many potters choose updraft kiln vents for their particular setup for a few reasons. For example, there’s no need to drill into the kiln because the fume hood sits above the kiln. You will still have to deal with ductwork and venting the hood to the outside air with this exhaust system, but no drilling is required.
Just like with a downdraft kiln vent, an updraft vent requires an exhaust fan and a flexible hose. This fan will pull room air and fumes out of the kiln room and disperse them into the ambient air outside. That being said, updraft kiln vents are not necessarily effective at pulling out all the fumes from the room since the air is not pulled directly from inside the kiln.
Where Can I Buy Kiln Ventilation?
You can easily search for “kiln vent” on sites like Amazon and DickBlick.com. In fact, DickBlick stocks the Vent-A-Kiln System, which is an updraft or hood vent that fits on top of your kiln. Amazon also has quite a few kiln vents, such as the Orton Ventmaster and the Skutt Wall Mounted Venting System.
You should also make sure to add a flexible hose to your list as well because every exhaust system needs a way to pull heat and air and direct it away from the kiln. The flexible hose is one of the most important components of the exhaust system as it will contain and pull air and fumes.
Kiln Room Ventilation Requirements
Besides calculating how much ventilation you’ll need for your kiln room, a few other requirements are necessary to make the most of your space.
For instance, you may think that you’ll need a ventilation system for every electric kiln, but unless you’re firing two kilns at the same time, you can use the same vent for different electric kilns. To be clear, every electric kiln that’s on and firing should have a kiln vent, but kiln vents can be shared between kilns if only one is running.
A kiln ventilation system should be turned on as soon as the electric kiln is turned on, so constant power and adequate power for both the kiln and the vent are required. You should also have at least 18 inches of uninterrupted space between the kilns and anything else.
If you have more than one kiln in the same room, they should be at least 36 inches apart from one another. This gives the kilns adequate space in order to achieve the temperatures they do safely so that nothing close by gets set on fire.
You should also be aware of what your homeowner’s insurance policy supports when it comes to the components of a kiln room. For example, if you have sprinklers in your kiln room (perhaps a garage or basement), you’ll need to make sure that the kiln’s heat does not set them off accidentally.
Fire suppression systems are great to have in your kiln room, as long as they’re not touchy enough to go off if the temperature rises a bit.
How Hot Do Kiln Vents Get?
Pottery kilns can get as hot as 300-500 degrees Fahrenheit on the exterior during kiln firings. This temperature depends on the cone you’re firing to within the kiln and where the kiln is at in the firing process.
As far as the ventilation system goes, this can vary depending on what type of vent you use and the ambient air temperature.
Since the majority of kiln vents are downdraft vents, where room air is pulled out, temperatures should be somewhere between 100 degrees and 150 degrees Fahrenheit.
You still don’t want to touch a kiln vent when your kiln is running or even after it’s done firing. However, the vent itself should not be as hot as the kiln exterior or interior, for that matter.
The flexible hose that directs the gases out may get hot as well, so be cautious of this if your kiln is running.
How to Vent a Kiln
Depending on the type of kiln vent you purchase, the installation process might differ from the following step-by-step guide. However, you should always consult your owner’s manual for the best way to install your brand-new kiln vent.
If you’re more of a visual learner, you can also watch Evolution Stoneware’s Janis Wilson Hughes install her kiln vent in a step-by-step video.
Step 1: Prepare the Kiln
There are two places where you’ll need to drill holes to not only remove air from the kiln but also replace it.
First, start by drilling small holes in the top of the kiln. The number and spacing of the holes will be specified in the owner’s manual of your new kiln vent.
Ensure that you are wearing a mask as you cut through the kiln brick, which shouldn’t be hard to do. In fact, you may not need a drill in order to cut through the kiln lid.
Next, drill holes in the bottom of the kiln as well. Make sure to vacuum the dust out of the kiln, so it doesn’t get caught in any projects after you’ve installed your kiln vent.
These holes on the bottom of the kiln will be responsible for removing heat and gases, while the holes on the top will replace the air within with fresh air.
Step 2: Drill Holes in the Bypass Box
Your kiln vent may or may not have a bypass box. That said, there will still be some sort of attachment piece that connects the kiln to the ducting that directs the gases out of the kiln room.
Within this piece, you’ll need to drill holes in order to dilute the kiln gases in the ducting with fresh air from the kiln room and surrounding area.
Step 3: Determine the Direction of the Blower Fan
Blower fans are sort of a misnomer in this case since you really want the fan you purchased with the kiln vent to draw air out of the kiln by pulling rather than pushing. This is also known as a centrifugal fan.
That’s why it’s important to determine which direction the fan will spin when it’s powered. Once you know the direction, you can easily make a mark on the fan for reference later when you’re putting the whole vent system together.
Step 4: Assemble Kiln Vent
Speaking of which, it’s time to gather all the pieces together. Connect the bypass box to the kiln and then to the ducting that will lead from the kiln out. Make sure the fan is set in the right direction. You now have a complete ventilation system.
Step 5: Attach Vent to the Outdoors
Attaching the vent to your kiln is the most important step, but that doesn’t mean you have to attach the other end to a specific point in your kiln room. In fact, some potters simply direct the end of the kiln vent (the exhaust duct) out underneath an open attached garage door or cracked window.
Step 6: Test Out Your New Kiln Vent by Venting Kiln Fumes
The only way you know if your kiln vent works is to actually fire it up and use it for the first time. This might be a good time to kiln fire only a few pieces, so you can focus more on the kiln vent than paying attention to the pieces within the kiln.
You should notice that any gases or unwanted fumes you might have smelled in the past are now gone. The air should be fresh, and the fan should earn its keep by pulling out air efficiently.