The Complete Exhaust Fan and Carbon Filter Buyer's Guide

Everyone knows plants need light and nutrition to thrive, but one thing that often goes overlooked is a grow room’s airflow system. Airflow and climate control are vital for the strength of any grow, but most people do the bare minimum to make sure their indoor garden’s breathing.

You see, airflow in your grow room or grow tent is about more than just opening windows and vents for fresh air. You need to make sure you’ve got air circulating around your grow and that your garden’s environment is at optimal conditions at all times.

The right exhaust fans, oscillating fans, and carbon filters will keep your grow room’s environment and plants thriving. Without them, your humidity levels, temperatures, and CO2 levels will be all over the place, and your plants will suffer.

That’s why we wrote this guide to give you the ins and outs of airflow in your grow room. We’ll help you understand exactly what fans and filters are, how they help your grow room, and how to choose the right ventilation setup for your grow room. Heck, we’ll even help you build your vent system and maintain grow room environments, too!

Table of Contents

1. What Are Exhaust Fans and Charcoal Filters?

• Exhaust Fans and Oscillating Fans
• Carbon Charcoal Filters
• Ducting and Connectors

Why Do You Need to Use Exhaust Fans and Charcoal Filters?

• What Are the Best Temperatures and Humidity Levels for Your Grow Room?

Airflow, Filtration, and Ventilation Throughout Your Grow Room

• Airflow
• Active Airflow
• Passive Airflow
• Filtration
• Ventilation
• A Quick Note on Air Conditioners and Heaters

How to Choose the Best Exhaust Fan and Charcoal Filter

• How Can You Figure Out What CFM You Need for Your Growing Area?
• What About Negative Air Pressure?

The Best Airflow Systems for Your Grow Room

• Editor's Choice
• Perfect for Small Grow Tents/Grow Rooms
• Perfect for Large Growing Areas
• Perfect Supplemental Fans
• Perfect for Circulating Air

Your Grow Room's Environment Depends on Airflow

Frequently Asked Questions

So if you’re ready to get your grow room’s airflow on point, let’s get to it. Strap in, because we’re starting off with a complete breakdown of fans and filters.

What Are Exhaust Fans and Charcoal Filters?

Your plants can’t thrive without the right ventilation and circulation for fresh air. To get the air your plants need, you’ll need equipment that helps you bring in, filter, circulate, and expel air. That’s where fans and filters come into play.

Exhaust Fans and Oscillating Fans

Exhaust fans and oscillating fans help bring air into your grow room or grow tent, circulate air around your garden, and push stale air out of your growing area. A variety of fans will help you achieve the airflow you want, and we’ll get into those shortly. What’s important to know is that fans are going to be moving air throughout your garden.

• Exhaust fans are cylindrical and work off of a large motor to push lots of air. They offer ports that are used to fit ducting over in order to direct the flow or air.

• Oscillating fans are semi-open-faced fans with large blades, just like the ones you find in homes.

Carbon Charcoal Filters

Charcoal filters, on the other hand, help filter the air your growing area receives. When air is pushed into a charcoal filter, the material inside helps trap large particles like dirt and dust, along with scent cells, to lower odors. 

So whether you’re concerned about the air coming into your garden or the air inside of your growing area, filters help keep the air inside your grow room the freshest it can be.

• The carbon medium (usually coconut or charcoal) sits inside of a metal cylinder, and when air’s pushed through, particles adhere to it. The air that comes out of the filter is then fresh and free of particles like dust and dirt.

Ducting and Connectors

Nothing in a ventilation system would be able to connect together and work properly if it weren’t for grow room ducting. From fans to filters, ducting helps direct air from one area into and around your indoor garden.

Ducting connectors are vital to grow rooms that need to put together multiple fans, filters, and duct work in a huge range of sizes. These connectors include:

• Duct connectors that connect one length of ducting to another.

• Split (Y or T) connectors help connect multiple lines of airflow together, usually stemming from one fan and the airflow going in multiple directions.

• Reducer/increaser connectors connect different-sized duct work together. For example, if you’re working with 6-inch fans but you want to connect to 4-inch ducting, and vice versa.

Why Do You Need to Use Exhaust Fans and Charcoal Filters?

There are plenty of growers that ask us, “Do you really need fans and filters in the grow room?” The answer is an overwhelming “Yes!” While choosing the right ventilation can be tricky, it’s important to make sure you have what you need to control the air coming into your indoor garden.

Adding fans and filters to your grow room will benefit your garden in a number of ways, including:

• Temperature Control — Just like in nature, your plants will suffer without the right temperature. That’s why you’ll need exhaust fans and even oscillating fans in your grow room to ensure your grow room doesn’t get too warm and your plants don't suffer.

• Humidity Control — Humidity is the amount of moisture in the air. Without the right amount of humidity, your plants will either dry up or become overwhelmed and droop. The right exhaust fan or oscillating fans will help level out the humidity in your grow room and help dial in the right environment for plants to thrive in.

• Maintain Optimal CO2 Levels — Carbon dioxide (CO2) is one of the key factors of plant respiration and metabolism activation. Exhaust fans and secondary fans can help you maintain the optimal CO2 levels your plants need to thrive. 

• Air Circulation — While exhaust fans help bring air into and push air out of your grow room, oscillating fans will make sure the air inside your garden is circulated. Plants suffer from stagnant air — not to mention it’ll start to smell — so it’s important to both keep fresh air in your grow room and to keep it moving while it’s in there.

• Improving Air Quality — When new air is pushed into a carbon filter, particles like dust and dirt that are in the air are trapped in the charcoal. When air leaves the filter, your plants get nothing but fresh, particle-free air. This will help stomata stay clear so your plants take in what they need to grow and thrive.

• Strengthening Plants — A small breeze against your plants’ leaves and branches will signal it to strengthen itself. Flimsy plants won’t be able to hold flowers or fruit, so a steady breeze will help branches grow strong.

What Are the Best Temperatures and Humidity Levels for Your Grow Room?

We wanted to take a moment to go over optimal grow room conditions. Running exhaust and oscillating fans — along with carbon filters — means nothing if you’re not sure where temperature and humidity levels should be for your grow room.

• Temperatures should be around 70 to 80°F while your lights are on (“daytime”), and 65 to 70°F while lights are off (“nighttime”).

• Note: Daytime and nighttime temperatures shouldn’t drop more than 10 to 15°F — otherwise your plants are going to shock themselves.

• Humidity levels for most plants are around 50 to 70 percent while growing, and 50 to 60 percent while flowering and fruiting.

• Most plants can waver between 40 to 60 percent humidity at any time, so the key is making sure it’s never too dry or too damp in your grow room.

• CO2 levels for most plants should be 1000 to 1300 PPM, and 1500 PPM if you’re going to enrich your plants’ CO2 levels.

Airflow, Filtration, and Ventilation Throughout Your Grow Room

Now that you have an understanding of how exhaust fans, oscillating fans, and charcoal carbon filters help your grow room, let’s talk about the science behind how each of these work. Here, we’ll take a dive into airflow, filtration, and overall ventilation of air and show you how each piece of equipment works to give your plants the environment they need to thrive.

Airflow

To begin, let’s talk about airflow. Airflow can be seen as the flow of air into and out of your growing area. There are two types of airflow your growing area is capable of utilizing. In fact, you might be utilizing one now and now even know it!

Active Airflow

With this style of airflow, air is mechanically moved into, out of, and around your grow room or grow tent. This is especially helpful in areas where plants can’t exchange and circulate fresh air, because a grow room without moving air will suffer.

• Exhaust fans are perfect for bringing fresh air into a growing area. They can also help push air into filters for odor reduction, and help push stale air out of your growing area quickly and efficiently.

• Duct fans will help your exhaust fan’s ability to keep airflow speed where it should be as it travels around corners and through long stretches of ducting.

• Oscillating fans help mechanically move air around your growing area to make sure the air your plants receive is always circulating.

• Ducting helps direct active airflow into your growing area. Without it, the wind from a fan would blow into the open air, having little affect on your indoor garden.

• Inline fans are often used in long stretches of ducting to help airflow travel at a consistent speed and volume. Keep this in mind when we get into finding the right size fans and filters for your indoor garden.

Passive Airflow

This is a non-mechanical form of airflow where air is allowed to travel freely into, throughout, and out of your growing area.

• This can be done by opening a window in your grow room, opening passive airflow flaps on the side of your grow tent, or even opening the door on your grow tent or grow room.

• Passive airflow is important for any garden, as it helps exchange the air inside your grow room with new air that can be filtered for clarity.

• You can also use passive airflow to cool down a growing area, as well as lower the humidity and CO2 levels in your grow room.

Filtration

After your air is pulled into your growing area, the best idea is to ensure it runs through a filter. This is for two key reasons:

• Higher Quality Air for Plants — Most carbon filters are filled with material (usually charcoal) that helps adhere dust and debris in the air to its surface. By doing that, the air that’s pushed out of the filter will be free of those particles that can clog stomata and keep plants from breathing properly. That way all the air circulated inside of the grow room is clean, and any air pushed outside will dissipate.

• Reduce/Eliminate Smells — Filters also help suppress the smells in your grow room that can leak out into the rest of your home or environment. Rodents and bugs are attracted to the scents your grow room gives off, and those scents are carried through the air. By filtering them, you’ll reduce the concentration of aromas in your grow room, in turn reducing the number of unwanted guests looking to your indoor garden for a buffet.

Ventilation

As you can see, the overall ventilation of your grow room relies heavily on fans and filters. While you could get away with passive air and no filters, it’s never guaranteed that your plants will get all the air they need — at the quality they need it — to maintain the perfect growing environment.

That’s why we recommend using at least one fan and one filter in your grow tent or grow room. Combined with passive airflow, you’ll be able to ensure your plants have fresh air to take it. Here’s the best way to arrange a ventilation setup for your growing area:

• The passive airflow outside of your grow tent/grow room will be your main source of air.

• Position an exhaust fan at the top of your growing area, as air rises and you want to capture it and push it back through a filter for your plants.

• Connect ducting from your exhaust fan into a carbon filter. Try to make the distance between your fan and filter as short as possible to avoid weak spots of airflow.

• Remember that if air has to travel through long distances, that air's speed and volume will be reduced.

• You can let air passively float out of your grow room through an open door or window, or you can use an active airflow approach and duct a second exhaust fan to push air out of a vent.

• If you want to push air out of your growing area, we suggest venting out of a vent port — like you would find in a laundry room — or by using a window vent. Don’t worry, they’re relatively cheap and super easy to install. Find more info on them here.

A Quick Note on Air Conditioners and Heaters

Just like in your home, air conditioners and heaters help change your grow room’s environment quickly. While this can be helpful in extreme circumstances, it’s important to use them sparingly.

The problem arises from how quickly they work to raise or lower levels in your grow room. Extreme changes in environment — quick changes, no less — can lead to mold and bacteria growth on your plants. Not to mention, extreme fluctuations in temperatures aren’t optimal for plants, so without being eased into their new conditions, they’ll have stunted growth.

Of course, when regulated properly, this isn’t an issue. But in growing areas that don’t face extreme changes in environment, the best form of ventilation is with passive airflow and active airflow via exhaust fans.

How to Choose the Best Exhaust Fan and Charcoal Filter

When it comes to choosing the right fans and filter for your grow room, there’s one calculation that will unlock the key to airflow success: CFM. Cubic feet per minute (CFM) is the measurement of how much air an exhaust fan can produce and how much a carbon filter can handle before they’re virtually ineffective. So if you don’t choose the right size (in CFM), you can overwhelm or underwhelm your plants’ growing environment.

How Can You Figure Out What CFM You Need for Your Growing Area?

Calculating the right CFM for your grow room is actually pretty simple. All it takes is measuring tape, a little bit of time, and a bit of math.

Here’s what the formula looks like:

(Volume of Growing Area) x (Number of Air Exchanges per hour) / (60 Minutes) = CFM needed to fill your room with air or the amount of air your filter can handle at a time.

So let’s break that down:

• To get the volume of your growing area, simply multiply the length x width x height.

• Take that number and multiply it by the number of air exchanges you want in your growing area. For most grow rooms, you’ll want to exchange your air about once every 3 to 5 minutes, or 12 to 20 times each hour. 

• Air exchange is necessary to ensure all the air in your growing area is fresh. Even filtered air will eventually stagnate, so exchanging air is important.

• Take that number and divide it by 60 to get the minimum CFM your grow room needs.

• Now, take that number and multiply it by 2. This will give you a rough estimate of the true CFM requirements your grow room needs, taking into consideration pushing air through filters, the distance air needs to travel, grow room heat, and humidity.

• Once you have that number, find the fan that will give you what you need.

• Keep in mind you’ll have two sizes you’ll be looking at: the CFM and the diameter size of the duct opening (4in, 6in, 8in, 10in, and so on).

To illustrate the point, let’s figure out the CFM requirements for a 6x6x8ft grow tent:

• The volume of this grow tent is 288 cu ft.

• In this grow tent, we’ll use 20 exchanges (1 per 3mins) — 20 x 288 = 5760.

• We’ll divide that number by 60 (5760 / 60) to give us a minimum requirement of 96 CFM.

• Now we’ll double that number to take into account grow room factors like heat and air pressure, which give us a requirement of 192 CFM. With that CFM size, we’ll be able to figure out what diameter size fan we need.

• In this case, something like the Yield Lab 4 Inch 190 CFM Charcoal Filter and Duct Fan Combo Kit would be perfect, as it’s enough to give your grow room all the air it needs to perform at peak conditions.

Now, of course, there are a number of factors that also come into play when it comes to CFM.

• For example, if you’re running ducting around your growing area’s ceiling, you’ll find that air travels a lot longer than 8ft.

• Therefore, you may need an extra bit of force to get air where it needs to go, like an inline fan.

When conditioning your garden’s environment (i.e., lowering/raising temperatures/humidity/CO2 levels), you’ll want a system of fans, not just one. For example, in grow rooms that need 192 CFM, ideally you'd use two 4-inch 190 CFM fans. This ensures that one fan will introduce fresh air into your growing area, and the other will help get rid of excess heat/humidity/CO2.

No matter what your setup is — a single exhaust fan and filter, or multiple high output fans and charcoal filters — the key to ensuring your grow room has the environment and airflow it needs to thrive is calculating your CFM requirements. From there you can find out how many fans you’ll need to achieve your grow room’s goals.

What About Negative Air Pressure?

Now, if you know a little about physics, you know that negative air pressure happens when the air exiting a given space is higher than the air it takes in. When this happens, you’ll notice your growing area start to pull inward. If you’re in a grow tent, you’ll see the walls and ceiling concave a little, but in grow rooms it may not be that noticeable.

Negative air pressure isn’t all bad. In fact, some negative air pressure is a good thing:

• Minimal negative air pressure is a sign that you’re effectively getting rid of particles that cause mold in your garden.

• It’s also a sign that your environmental conditions are being regulated and not staying stagnant.

However, excess negative air pressure has its downsides, too. Aside from pressure pulling on your walls, risks include: 

• Unfavorable Environment — Too much air leaving your growing area and it’s likely that your grow area’s environment is too cold and/or dry.

• Lack of Vital CO2 — When you’re pushing significantly more air out than you are taking in, the air coming in will have little effect on your plants. That means that while they’re not receiving all bad air, they’re not really receiving CO2-rich oxygen, which is necessary for plant growth.

To avoid too much negative air pressure, switch from a passive airflow intake to active airflow intake. The key is to even out the amount of air coming in as it is coming out.

Tip: If you find you’re pulling too much air out of your grow room, consider using a motor speed controller to help regulate the speed of your fans. Keep in mind when you’re lowering environmental conditions, you’re going to create a little bit of negative air pressure. Remember:Minimal pressure is a good thing, but too much is a problem.

The Best Airflow Systems for Your Grow Room

Let’s face it — even with all the best info, it’s still a pain trying to figure out the best fans and filters for your grow room or grow tent. That’s why we tested a number of exhaust fans, oscillating fans, and charcoal filters to come up with the best setup for your plants.

Yield Lab 6-Inch 440 CFM Charcoal Filter and Duct Fan Combo Kit — Editor's Choice

This 6-inch fan and filter combo can filter enough air for up 8x8ft grow tent or grow room!

Of course, if your air has to travel around turns and curves, this setup will still fill a 6x6ft grow tent or grow room with CO2-rich air — and that’s on full power. Using the built-on fan controller, you’ll be able to adjust that output for pretty much any grow room.

The exhaust fan also has an on-board variable speed controller in case you need to adjust your fan’s speed. Turn the knob to dial down the speed of the fan or to raise temperatures. When coupled with another fan, these can be adjusted to give you virtually complete control over humidity, CO2 levels, and temperatures for optimal growth.

The carbon filter is filled with charcoal that helps ensure the air coming from the area outside your grow room is clear of harmful particles — not to mention keeping grow room odors down. This includes pollen, dust, and dirt that can clog and infect your plants, as well as cells carrying scents.

These carbon filters last at least 6 to 8 complete growing cycles, giving your plants around 2 to 3 years of use — that’s longer than most grow bulbs you’re going to use.

Yield Lab 4-Inch Pro Series Fan with Speed Controller - 190CFM — Perfect for Small Grow Tents/Grow Rooms; Best Paired with Yield Lab 4-Inch Purifier Activated Charcoal Filter

If you’ve got a 4x4ft grow tent or a 2x4ft grow tent or closet grow room, this is the fan you’re looking for.

This grow room fan comes equipped with twin intake and exhaust ports. Unlike most other exhaust fans that only have one port, this fan can be used as an intake, exhaust, and inline fan.

In addition, the fan also includes a built-on speed controller, so you'll have full control over your grow room or grow tent's environment including its climate and any unnecessary odors. That makes this one of the most versatile grow room fans around.

Paired with the Yield Lab 4-Inch 190 CFM filter, this exhaust fan and carbon filter combo is perfect for small grows. From your closet to a covered grow tent, this fan will give your plants the air they need to regulate and maintain the perfect grow room environment. And with the speed controller, you'll be able to ensure that speeds and strength are as high or low as you need them to be.

If you're a grower who just wants to grow a few plants, or you want to keep your growing area small, this is the perfect fan for the job. It'll get you results without damaging your plants!

Phat Fan 12-Inch, 1708 CFM — Perfect for Large Growing Areas; Best Paired with Phat Filter, 12x39in, 1700 CFM

If you’re looking for a large amount of air inside your growing area or want to get a lot of air out of your grow room, this Phat Fan is the exhaust fan for you.

With the ability to provide air for or remove air from your grow room at 1708 CFM, this fan is made to service large grow rooms with a lot of plants. We’re talking at least 10x10ft grow tents and 15x15ft growing areas. With this fan, you'll get the perfect amount of high power for larger spaces, making it ideal for any larger-scale growers.

In such big grow rooms, you’re going to need multiple fans — but you'll also want a fan like this to ensure both climate and odor control are handled properly. Coupled with the 1700 CFM 12-Inch Phat Filter — and maybe a few 6-inch inline fans for those larger grow rooms — you’ll be able to effectively stabilize your growing environment and reduce smells.

If you're running a larger grow room or grow tent, you'll want this Phat Fan. It'll give you both the climate and odor control you need to ensure your grow room and your plants are healthy.

Yield Lab 6-Inch Booster In-Line Duct Fan, Yield Lab 4-Inch Booster In-Line Duct Fan  — Perfect Supplemental Fans

These booster fans are surprisingly versatile and extremely effective.

The primary function of these booster fans is to help assist 6-inch and 4-inch exhaust fans keep their airflow consistent across long stretches of ducting. They do this exceptionally well, but that’s just their primary function.

Booster fans are perfect for very young plants, too.

Seedling and clone growing areas need a little more airflow than simple oscillating fans will give you, and that’s where booster fans help. With fans like these, you'll get the air circulation necessary to keep your grow room or grow tent thriving.

Just use one of these fans in your seeding/clone area and they’ll get the breeze they need to grow strong. At the same time, your plants will receive the CO2-rich air they need to keep their environment stable. If you're looking for the perfect supplemental fan for your grow, it doesn't get much better than these 6-inch and 4-inch booster fans.

Active Air Heavy Duty 16-Inch Metal Wall Mount Fan — Perfect for Circulating Air

Rounding out the list of vital fans for your grow room or grow tent is this large oscillating fan. While you could go with a few smaller clip fans, we recommend this 16-inch oscillating fan for two key reasons:

1. Variable Speeds — Whether you need a heavy breeze or a gentle one, the varying speeds on this fan can be adjusted for large and small grow rooms alike.

2. Coverage Area — With a 16-inch surface, the breeze from this fan can be felt by more than one part of a plant. Instead, it will cover at least 3 to 4 plants.

So whether you’ve got a few plants or a lot, an oscillating fan like this is what your plants need to keep air circulating around your growing area.

Your Grow Room’s Environment Depends on Airflow

In the end, choosing the right fans and filters for your grow room is vital for your grow room’s environment. Without the right amount of CO2, proper humidity, and correct temperatures, you can lead your plants down the road to destruction. So it’s important to choose the right airflow equipment to keep your grow room’s environment at optimal conditions.

To determine what the best setup for your grow room is, it all starts with the CFM your grow room or grow tent needs. From there, you’ll want to find the appropriate fans to give your plants what they need.

Once you’ve got the right equipment, you’ll be able to dial in and maintain your grow room’s environment better than by opening windows and doors. So now that you have the foundation for your indoor garden’s airflow, it’s time to build the environmental control system to help your grow room — and your plants — thrive.

Frequently Asked Questions

1. What fans and filters do I need?

While you may not need an entire HVAC system for your plants, there's some basic airflow equipment that all grow rooms absolutely need. Let's take a look:

• At Least One Exhaust Fan — This will help either bring air into your growing area or push it out.

• With two or more exhaust fans, you’ll have better control over temperatures, humidity, and CO2 levels.

• Ducting — Whether you’re bringing in air or pushing it out, ducting will help direct air into/out of your grow room efficiently instead of blowing into the open air.

• At least Two 6-Inch Oscillating Fans — These fans will help circulate the air inside of your grow room so your plants aren’t breathing in stagnant air.

Now, while we highly recommend a carbon filter, they’re not 100 percent necessary. Believe it or not, some sources of air are actually fresh enough to give your plants unfiltered air, like grow tents in homes with clean air. Moreover, if you don’t mind smells outside of your garden and your oscillating fans keep stomata clear, there’s no dire need for a carbon filter.

We will stress, though, that the lower the air quality outside of your growing area, the worse quality air that will go into your garden without a filter. So unless you can guarantee your air source is fresh and clear of most debris — which, in reality, you can’t — get a carbon filter.

2. How do I set up my exhaust fans and carbon filters?

Setting up your grow room’s airflow and filtration equipment is surprisingly easy. Really, it all comes down to four functions:

• Intake of fresh air.

• Filtration of that air.

• Circulation of air.

• Stale/stagnant air out.

When you think of it this way, all you have to do is fill in the gaps with passive and active airflow. That said, here’s how we suggest setting up your grow room’s fans and filter:

• Start by setting up your oscillating fans so that there’s a breeze throughout your entire canopy.

• Depending on the size of your fans, you can either position them above your plants or at their canopy. Large fans can circulate air from above well, whereas small fans do best when circulating close to the canopy.

• Remember to keep fans from blowing too hard. The point of these fans is to circulate air around your canopy and garden, so if they’re going too fast, you’ll risk plant damage and environmental issues.

• Position your intake/exhaust fan toward the middle/bottom of your grow room or grow tent. This is where you’ll intake cool air for your grow room (opposed to warm air from up top).

• If you’re unable to position your fans at the bottom of your growing area, place it as low as you can so that the air around it is as cool as possible.

• Hang your charcoal carbon filter above your plants. This will ensure that the fresh air forced out of your filter fills your growing area.

• Connect ducting from your exhaust fan into your carbon filter and turn on your fans — now your grow room will be able to get the airflow it needs.

Now, if discretion is the name of the game and you want to keep heat and smells to a minimum, we suggest getting another exhaust fan, length of ducting, and a second filter.

• Hang your second exhaust fan toward the top of your growing area to draw in warm and unwanted air.

• Run ducting from your fan to a window vent or simply outside of your growing area. This will help unwanted air get out of your growing area, reducing the heat in your growing area.

• For those who want to eliminate odor, run ducting from your fan into a second carbon filter instead of outside.

3. How do I control the temperature/humidity of my grow room?

Controlling your grow room’s environment is all about air intake and exhaust. By controlling the amount of air coming in, circulating, and leaving your growing area, you’ll be able to control your grow room’s environment.

Now, if you’re committed to controlling your grow room’s environment without A/C units and heaters, you’re going to need at least 1 intake fan and 1 exhaust fan. Here’s how you do it:

• To raise grow room temperatures, lower the speed of both your intake and exhaust fans. This will allow the heat that’s naturally occurring in your grow room via condensation and equipment running (on top of external conditions) to build and stay inside of your grow room while slowly being filtered in and out.

• To lower grow room temperatures, increase the speed of your intake fan and slightly lower the speed of your exhaust fan. This will allow for cooler air to enter quickly and leave slowly without too much heat build-up.

• To lower humidity, increase your intake and exhaust fan speeds. This will allow you to take in lots of air and push it out quickly, getting rid of moisture quickly.

• If possible, it may also help to increase the speed of your oscillating fans. This will help get rid of moisture faster.

• To increase humidity in your grow room, lower your intake fan and drastically reduce your exhaust fan. You will need air and moisture to build up in your garden, so do not completely eliminate fans, but reduce them until you’ve reached optimal conditions.

We should note that if you haven’t done so already, make sure you have a thermo-hygrometer to check both temperature and humidity. Normal thermometers only read temperatures, which are only part of the airflow equation.

4. How can I automate my airflow system?

Grow rooms thrive when they have consistent environmental conditions, and airflow is one of the best ways to achieve those conditions. But automating your exhaust fans and filters to maintain the optimal environment is about more than setting timers. Automating your airflow system is all about knowing where conditions need to be and getting the right controller to keep them there.

That’s why we recommend one of these three controllers for your airflow equipment:

• LTL Digital Temperature Controller - Cooling — With a controller like this, you set your hottest temperature, and when your grow room or grow tent reaches that temperature, the fans kick in to lower it.

• LTL Day/Night Fan Speed Controller — This controller lets you set both nighttime and daytime temperatures, and once your grow room reaches those temperatures, exhaust fans will help lower them. This helps avoid fluctuations in environment all day long.

• iPonic 614 Environmental Controller — While expensive, this controller will activate exhaust and oscillating fans when it detects unfavorable environmental changes. From CO2 levels to humidity and temperatures, with a controller like this you can automate your airflow and filtration for optimal conditions 24/7.

5. How much will it cost for me to use my airflow equipment?

Exhaust fans and oscillating fans usually take the least amount of energy to run. Compared to grow lights and even hydroponic systems, exhaust fans and oscillating fans make up for a minute amount of energy in the grow room.

That said, start by looking into the wattage draw of your fans and any other airflow equipment that uses power. This will let you know how many watts of power will be drawn while your airflow equipment is in use.

• Note: Wattage can usually be found on a sticker or somewhere on the fan itself. If it’s not there, it should be in the instructions or packaging that came with your fan. If all else fails, there are meters you can use to read the wattage draw of an electrical component.

After that, you’ll need to take a look at your electric bill and see how much you’re charged per kWh. Keep in mind that this fluctuates depending on the season, time of day, and how much energy you use overall. Nonetheless, make sure you get the rates you’re charged for electricity.

Once you’ve got the total wattage draw of all your equipment, it’s time to do a little math:

• Take the total wattage of your equipment and multiply it by the number of hours you’re using said equipment.

• Divide that number by 1000 to give you the kW you’re using while the equipment’s running.

• Take that number and multiply it by the rates on your electric bill.

Let’s put this into practice. In this example, we'll use a 10-inch fan that uses 228w, a 6-inch fan that uses 135w, and three small oscillating fans at 15w each:

• While these fans are running, they’ll be using 408w of power.

• For a rough estimate, let’s say that you’ll run your fans while lights are on. You'll be running them at least around 12 hours. So 408w multiplied by 12 hours is 4896.

• Divide that by 1000 and you get ~4.90.

• Now multiply that by the kW/h rate — we'll use an example of $0.12/kWh. So 4.9 multiplied by .12 is ~.59.

• In total, your fans would cost you $0.59/day to keep their growing environment stable, and that’s not bad at all.