Setting up a sealed indoor garden is more expensive but, if done correctly, it should give you the maximum ability to dictate and control temperatures, CO2 levels, humidity, and disease, 24 hours a day, 365 days a year.

Temperature

Now, some of you might be scratching your heads at this point. Isn’t a totally sealed room going to get really, really hot from all the grow lamps? And what’s going to stop the plants from suffocating to death, right? Well, these are the same challenges that face every indoor gardener. It’s just that the “sealed room” approach tackles these challenges in a different way.

First, let’s look at the whole issue of temperature. Every indoor gardener knows that it’s absolutely vital to control this key factor for successful cultivation. Plants perform better in optimum temperature ranges without large fluctuations. So how do we deal with all the heat produced when we fire up our grow lamps, dehumidifiers, pumps and ballasts? The answer is short and simple. AC, my friend! Air Conditioning is the only solution to beat the heat of a sealed room. Here’s an AC rule of thumb to help you spec the right unit:

You will need 4000 BTUs of cooling per 1000 Watts of lighting.

Example: 6 x 1000W= 6000 Total Watts of lighting  x 4000 BTUs= 24,000 BTUs of cooling required.

Note: the term “BTU,” or British Thermal Unit, is used to describe the power of heating and cooling systems. When used as a unit of power, BTU ‘per hour’ (BTU/h, that is, BTU divided by hour) is understood, though this is often abbreviated to just “BTU.”

Be aware that there are companies that have designed units specifically for hydroponic setups that can be installed without the expense of hiring in a certified electrician. These same units can handle the demands of constant cooling year around.

CO2

Next, let’s take a look at CO2 levels. We all know that plants need CO2 in order to photosynthesize, so we’re going to supply this if we’re not relying on fresh air ventilation. Growers using standard ventilation can maintain normal atmospheric levels of CO2 in their indoor gardens. If they wish to add more, however, they often encounter a dilemma. What’s the point of injecting extra CO2 into your indoor growing environment if it’s going to be vented out again before your plants have had a chance to benefit from it? Historically, growers have shut down their ventilation systems temporarily to give their plants time to absorb the extra CO2 but then, of course, temperatures begin to rise! It’s a bit like trying to fit a carpet that’s too big for the room!

With a sealed room you can inject optimum amounts of CO2 without worrying that it’s all being vented away. There are two standard ways to inject CO2 into your environment: using a burner, where natural gas or propane is lit as a flame and the off gas produces CO2; and bottled gas where you open a bottle of CO2, enriching the air directly. Using a burner is most common among larger setups of 6000 watts or more, due to the amount of CO2 required to drive PPMs from 400-2000PPM. This method can create additional heat due to the flame, but keep in mind that using AC can easily combat any heat issues you may have. There are also water-cooled CO2 generators on the market these days. The bottled CO2 is ideal for smaller rooms and can be equipped with diffusers that automatically release the CO2 gas as needed. Many growers have found that having CO2 enriched air in a grow room can produce up to 30% more yield.

Humidity

Next, let’s tackle humidity. Without venting moist air to the outdoors, the humidity in the indoor garden will quickly rise as the plants give off water vapor (transpiration). If humidity levels are too high it can be a cue for pathogens to attack and growth rates to slow dramatically. However, venting presents its own challenges. The outdoors will always dictate the humidity indoors as most places in North America have fairly high levels. In a sealed room you can control humidity to precisely where you want it, all day, every day, using dehumidifiers and air conditioners. Much like air conditioners, dehumidifiers are available in many sizes and properly selecting one for your size room is important. Lower humidity levels are often preferable towards the end of many plants’ flowering cycles to decrease the probability of mold and mildew.

Pests

Finally, a huge advantage of growing in a sealed room is disease and pest control. As long as you make sure you (the grower) stay clean, you can be sure that your environment is sealed from any nasty critters who see your plants as breakfast, lunch or dinner. To explain why a sealed room is ideal for disease control, ask yourself this question: how did my room get diseased in the first place? Much like humans, our environment means everything. It could be large temperature swings, high or low humidity, outside influences such as outdoor crop sprays, insects or anything else floating around. In a sealed room, you not only protect yourself from negative outside influences, but you also strive to create the environment you think is best – independent of what’s going on outdoors.

The sealed room concept has been successfully used for many years in gardens of all sizes.I hope that I’ve managed to inspire thoughts on how to bring a perfect environment to your garden!

Happy growing!

Greetings Urban Gardeners.

Let’s take a look at how we can get the most out of our hydroponic nutrients, otherwise known as “nutrient management.” Now, to the skilled grower, nutrient management represents an opportunity to enhance plant growth, enjoy bigger yields and achieve higher overall crop quality. However, to the novice it can represent a difficult challenge or even a complete mystery! The difference is in knowledge, understanding, environment and equipment.

Here are six questions to test your nutrient knowledge. Do you already know the answers?

Your nutrient solution should be maintained at around 68 °F (20 °C) for the best combination of oxygen content and uptake by the roots.

Q2) What is the “dissolved solids” content of the water you use to mix your nutrient and does this content vary greatly from season to season? Does your water supplier provide you with good water from one reservoir at one time of the year and bad water from a different reservoir at another?

Test your water with an EC meter before adding anything to it.

Q3) Are there any components (such as high levels of calcium or magnesium) in your water that could affect the availability of other nutrient  elements? Have you considered the presence of sodium chloride from sea-water contaminating your water supply?

Ask your water supplier to provide you with an analysis of your water. Some grow stores also offer this service.

Q4) What is the “EC” or strength of your nutrient? Do you mix special nutrient blends for different kinds of plants and for each stage of the crop’s lifecycle, or in response to different environmental conditions like high temperatures and low humidity?

If you are unable to prevent temperatures in your indoor garden from rising too high, you can decrease the stress levels for your plants by decreasing the strength of your nutrient solution.

Q5) Does the pH of your nutrient stay within a reasonable range, or does it drift up and down significantly? How quickly?

It’s quite normal for the pH of your nutrient solution to rise (say from 5.8 to 6.5) over the course of a few days – but greater changes could indicate the presence of pathogens in your nutrient solution from contamination or from sick plants that may spread disease to the rest of your crop.

Q6) Do you change your nutrient often enough to prevent imbalances from salt accumulation or deficiencies from nutrient exhaustion?

It’s really important to change your nutrient solution regularly because it helps to minimize the wastes your plants discard into the nutrient. Did you know that, as plants transpire and nutrient levels drop in your reservoir, the EC or strength of the nutrient can rise to dangerously high levels?

What’s In Your Water?

Water quality is a crucial issue for all gardeners. Success comes easier with soft water. Just add the right combinations of nutrients to the water and you’re off to a great start. However, if you have very hard water, or water contaminated with sodium, sulfide, or any number of heavy metals, your first step may be to filter your water using “reverse osmosis.”

The best way to find out what’s in your water is to obtain a seasonal water analysis through a lab. If you’re on a municipal water system, call your water district and request a copy of their most recent analysis. Keep in mind that a good analysis at one time of the year does not mean that the water quality will remain good throughout the year. During dry seasons water suppliers often switch to a different reservoir with different water quality.

Another approach – highly recommended – is to check your water regularly yourself with a dissolved solids meter, also called an electrical conductivity (EC) or parts per million (ppm) meter. These instruments are one of the most important tools for a grower to use regularly. By measuring the EC (ppm) of your source water routinely before adding nutrients, you will be able to tell if your water supply is consistent, or changing.

How Does a Conductivity Meter Work?

All dissolved solids instruments work in essentially the same way: they measure the electrical conductivity of the water. It is the dissolved salts in most water that allows it to conduct electricity. Pure water is a poor conductor since there are none of the conductive salts found in impure water. Purified water will show no, or very low, salt content (conductivity) when tested with a dissolved solids meter.

It is not uncommon to find high levels of salts in well water or municipal water supplies. Calcium and magnesium carbonates are among the most common ingredients in tap water and in well water. In fact, water “hardness” is defined as a measure of the water’s content of calcium and magnesium carbonates. In some regions sulfates can also reach high levels in water supplies.

Since calcium and magnesium are important plant nutrients, water with reasonable levels of these elements can be just fine for hydroponic cultivation. However, even a good thing can become a problem if the levels are too high. Generally, a calcium content of more than 200 PPM, or 75 PPM for magnesium, is on the verge of excessive for most hydroponic applications. An excess can cause other important elements in the nutrient solution to “lock-out” and become unavailable. For example, excess calcium can bond with phosphorus to make calcium phosphate, which is not very soluble and therefore not available to the crop. If magnesium bonds with phosphate it becomes completely insoluble and unavailable to the plant. The key to success is to start with decent water and add the right combination of nutrients.

Nutrients – A Question of Quality

What makes a quality nutrient? Here are some questions to ask. Some answers may be harder to find than others!

• How pure are the ingredients?
• How consistent is the product?
• Is it properly labeled with ingredients and NPK?
• How reputable is the manufacturer?
• What ingredients are in there and how are they combined?
• Does the product contain contaminants from poor quality control?
• If it is a liquid, did the manufacturer use R/O or purified water in the blend?
• Does the manufacturer have a quality control (QC) program like safety sealed bottles so you know it is pure and has not been tampered with?
• Are there any hidden or ‘mystery’ ingredients?

Too Hot, Too Cold

The temperature of your nutrient solution is another important factor. If your solution is too cold, seeds won’t germinate, cuttings will not root and plants will grow slowly – or stop growing and die. If it’s too hot, the same seeds won’t germinate, cuttings won’t root and plants will die from oxygen deficiency, or they will succumb to pathogens that thrive in higher temperatures, or simply bite the bullet due to temperature stress. Most plants prefer a root zone temperature range between 65 and 72 °F (18 to 22 °C), cooler for winter crops, warmer for tropical crops. When adding water to your reservoir it is a good idea to allow it to come to the same temperature as the water in the root zone before starting circulation pumps.

Remember, plant roots have evolved in a soil environment where temperature changes occur slowly, tempered by the thermal mass of the earth. Rapid temperature changes in the root zone can cause shock and invite root disease.

Water pH

A subject that is often discussed but rarely understood by many growers is nutrient pH. Plants normally grow best within a pH range from 5.5 to 6.8. Generally we worry about pH and its affect on nutrient availability. For example, if pH is too high, iron may become unavailable. Even though your nutrient solution may contain an ideal amount of iron, your plants may not be able to absorb it, resulting in an iron deficiency – the plant’s leaves will yellow and weaken.

On the other hand, hydroponic plant foods usually contain special “chelates” that are designed to assure iron availability, even at higher pH ranges. The result is that your crop will grow reasonably well even at higher pH levels. Nonetheless, high pH can damage plants in other ways. The cause of a high solution pH can be fairly complex. Most city water supplies contain calcium carbonate to raise the pH of the water and prevent pipes from corroding. As a consequence you are starting with water that has an abnormal pH: typically 7.5 to 8.0 for city water.

One method of dealing with the high pH of city water is to mix in fresh nutrient, let it stand for a while to stabilize, then test and adjust the pH. With city water supplies you will often have to add a solution of pH down (usually phosphoric acid) to lower the pH to the suitable range for most plants.

As your plants grow it is a good idea to occasionally test the pH and adjust it if needed. You can safely allow pH to drift between 5.8 and 6.8 without adjustment. In fact, constantly adjusting the pH in your system to maintain a perfect pH of 6.2 can do damage. It is common for pH to drift up for a while then down and up again. This change is an indication that your plants are absorbing nutrient properly. Adjust pH only if it wanders too far, below 5.5 or above 7.0 for example.  A pH below 5.5 or above 7.0 can spell trouble but don’t overreact. An apparently sudden and dramatic shift in pH can be the result of a malfunctioning pH meter. If in doubt, double-check with a reagent (color match) pH kit before adjusting your solution. Also remember that pH meters are temperature dependent. Read and follow all of the instructions that came with your meter or test kit. I know of at least one case where a grower lost a crop due to a defective pH meter after over-correcting nutrient pH.  Use a meter as well as a color-match test kit to double-check your pH.

Big pH swings can also indicate strong microbial life in the nutrient solution and root zone.  Microbes can change the pH to meet their needs.  The best way to manage this is to introduce beneficial microbes into your nutrient solution and the plant’s root zone. These microbes are nature’s little plant helpers.  The beneficial fungi typically help plants grow bigger, stronger and more effective root systems. The beneficial bacteria typically populate the root zone and protect the roots from bad microbes and environmental stress factors.

Time For a Change?

How often should you change your nutrient solution? That’s one of the most common questions asked and one of the most difficult to answer. Many people have tried to come up with a simple, easy-to-follow rule … once a week, every two weeks – but they’re all wrong! They’re wrong because there is no simple answer. It all depends on the plant variety, the number and size of your plants, their stage of growth, the capacity of the reservoir, the kind and quality of nutrient you use, water quality, environmental conditions such as temperature and humidity, and the type of hydroponic system used; there are so many factors that the answer is not obvious. Instead of a simple answer, what we need is a procedure that takes many of these variables into account and is responsive to changing conditions.

It sounds complicated, but it’s actually quite simple. All it takes is a little monitoring and some basic record keeping.

• Start with a fresh reservoir of nutrient and make note of the date, pH, and EC or PPM of the solution.
• As you run the system, the level will drop in the reservoir. Note the EC/PPM level then top-up the reservoir with fresh water. Test again for nutrient concentration. If the nutrient strength has dropped significantly, add a bit of nutrient to bring it back up to specs. Be sure to record how much water you added to top-up the reservoir. Repeat the procedure every time you top up the system, carefully recording the amount of water added.
• When the total amount of water added equals the capacity of your reservoir it is time to drain and replace all of the nutrient solution.

For example, imagine a hydroponic system in a cool greenhouse in the spring with 24 strawberry plants and a nutrient capacity of 20 gallons. Typically, such a system might require about five gallons of added water each week. After four weeks the plants will have transpired 20 gallons – the capacity of the reservoir. You need to completely drain and replace the nutrient every four weeks in this example.

Now imagine five tomato plants with a 20 gallon reservoir. They are fully mature, growing and producing quickly. It is hot and dry. Each plant pulls in a gallon a day so you are adding five gallons a day. After four days it is time to change the nutrient. It may be best to use a larger reservoir since the EC flux in this case will be pretty high.

Fascinated? Read on in the second installment of this feature in Issue 5 …

Dan’s Method – Calculating By Room Volume

You will find many calculations on the web for sizing a fan for ventilating indoor gardens; however, what many of these calculations fail to take into consideration is the friction loss on carbon filters and increased temperatures from HID lights. So here’s my calculation method, which you can use as a guide for sizing an exhaust fan for a growing area. Keep in mind that this calculation will give you the lowest required CFM (Cubic feet of air per minute) required to ventilate the indoor garden.

Step 1 – Room Volume

First the volume of the room needs to be calculated. To calculate, multiply length x width x height of growing area. For example: a room that is 8′ x 8′ x 8′ will have a volume of 512 cubic feet.

Step 2 – CFM Required

Your extraction fan should be able to adequately exchange the air in an indoor garden once every three minutes. Therefore, 512 cubic feet / 3 minutes = 171 CFM. This will be the absolute minimum CFM for exchanging the air in an indoor garden.

Step 3 – Additional factors

Unfortunately, the minimum CFM needed to ventilate a indoor garden is never quite that simple. Once the grower has calculated the minimum CFM required for their indoor garden the following additional factors need to be considered:

• Number of HID lights: add 5% per air-cooled light or 10-15% per non-air cooled light.
• CO2: add 5% for rooms with CO2 enrichment
• Filters: if a carbon filter is to be used with the exhaust system then add 20%
• Ambient temperature for hot climates (such as Southern California) add 25%; for hot and humid climates (such as Florida) add up to 40%.

An Example

In our 8’ x 8’ room we have 2 x 1000w air cooled lights, and we plan to use a carbon filter. We also plan to use CO2 in this room. The ambient temperature is 90 °F (32 °C), however, we will be using air from another room that is air-conditioned. Here’s the minimum required CFM to ventilate the room:

1)    Calculate the CFM required for room (see above).
2)    Add 10% (for 2 air cooled lights).
3)    Add 5% of original CFM calculation (for CO2).
4)    Add 20% of original CFM calculation for the carbon filter.
5)    Air is coming from an air-conditioned room so no need to add any other percentages.
6)    CFM = (171CFM) + (171CFM x 10%) + 
(171CFM x 5%) + (171CFM x 20%) + ( 0 )
= 231CFM.

This is the absolute minimum CFM required to ventilate your room.

The next step might seem to match the closest fan to this CFM. However, for this example I’d choose a six inch fan with a CFM of around 400 or more, and a 6 inch carbon filter to match. The extra CFMs may seem a bit excessive (calculations on most indoor gardening websites would recommend a 4” fan and a 4” carbon filter) but it’s always better to over-spec since we need to compensate for air resistance in ducting too.

Also, as we are using a carbon filter we will need to match the fan with the filter so that the fan that will neatly fit onto the filter.

Note: If all the variables are kept the same and we changed the room size from 8’ x 8’ to a 12’ x 12’, then the minimum required CFM would be 519 CFM.

The All-Important Inflow!

An intake port can be anything from a gap under the door to an open window – even a hole in the wall. The best place for an intake port is diagonally opposite from your exhaust fan; that way, air has to pass across the entire room – very efficient. You can put a piece of screen over the opening to keep insects and animals out, a piece of A/C filter to keep dust out, or a louvered shutter or backdraft damper that opens when the fan turns on and closes when it turns off. You can also use a motorized damper. This gets installed in-line with your ducting and is plugged into whatever device controls your exhaust fan. When your fan turns on, it allows air to pass. When your fan shuts off, it seals completely, preventing CO2, air, etc. from passing. You can get creative with these devices and use one fan to control two rooms, etc.

One additional note about intake ports: you will see much better results from your exhaust system if you install a second fan to create an active (as opposed to passive) intake system. Normally, when your exhaust fan sucks air out of your room, air is passively going to get sucked back into the room. By installing a second fan on the intake side, you will reduce the amount of negative pressure created in the indoor garden, thereby cutting down greatly on the amount of work the exhaust fan has to do and allowing much more air to pass through. If you’re not sure or you don’t want to spend the money, start out with just an exhaust fan. If it’s not performing as well as you thought it would, try adding an intake fan – you’ll smile when you see the difference!

Fred’s Method – Calculating By Wattage

Hello there. First off, I’m used to working with Celsius, not Fahrenheit, but I’ve done my best to provide formulas for both. My method for calculating fan requirements does not cover active cooling with air conditioning systems or cool-tube designs. We’re talking about everyday grow chambers here, totally enclosed for air-flow control, with no large amounts of radiant heat into or out of the box. Your mileage may vary some for these reasons.

Right then, let’s get started:

1) Start at the beginning and design this right! Before you even buy or cut anything for your new project, determine the highest temperature that your intake air will ever be when lights run. Call this T (inlet).

2) Use these formulas to determine the difference in temperature you can tolerate. 80 °F (27 °C) is just about the optimal for growing most plants. You can go up to 76 °F (30°C) if you have to, but aim for 80 °F (27 °C).

Tdiff = 27 °C – T (temperature of inlet air)

3) Add up wattage for all power sources in your indoor garden. Lights, pumps, heaters, humidifier, radio, coffee maker, whatever! Add it ALL up and call it Watts. If it is on for more than three minutes and uses more than a watt, add it up. This will make your number worst-case and therefore a conservative value.

4) Compute the absolute minimum fan power you will need using the following formulas. Fan power is measured in the amount of air (cubic feet) shifted per minute. The formula below is the minimum fan rating you must have to achieve your temperature goals. You will have to increase fan power to compensate for duct constriction, small inlets, carbon scrubbers, screens, or other items that block airflow.

CFM = 1.75 x Watts / Tdiff (in Celsius)

If you prefer to work in Fahrenheit, try this formula:

CFM = 3 x Watts / Tdiff (in Fahrenheit)

5) Get at least this fan power or don’t come and ask questions! If you are going to have more than one fan, they should be mounted side-by-side rather than inline if you want to add their different CFM ratings. For inline fans, use the lowest air-flow rating of all fans in the path. A fan on the inlet and a fan on the exhaust of the box are considered inline fans. Fans just circulating air inside the indoor garden should not be counted for airflow but must be included in your initial wattage calculations.

Ok, to see these formulas in action we’re going to have to do a little number crunching:

An Example

Ok, let’s say you have 2000 watts in a 8 foot by 8 foot room with an 8 foot ceiling height.

So what amount of air do I need to move to keep the room at 82°F (28°C)? My incoming air temperatures are 68°F (20°C) during the lights on period.

Tdiff = 28 – 20 = 8°C

For Celsius the formula comes out at:

CFM = 1.75 x 2000 / 8 = 438 CFM

For Fahrenheit we get the following:

Tdiff = 82 – 68 = 14°F

CFM = 3 x 2000 / 14 = 429 CFM

Here’s a quick look-up chart to show some further examples:

Remember, Tdiff shows how much your temperatures will rise above your inflow air temperature for a given wattage and air movement.

* Just a humorous example. 1000 watts of light with a PC computer fan (15 CFM) – temperatures rise 189°F according to this formula!

If you are adding any carbon scrubbers or extensive ductwork, this is where you add to the fan size to account for air pressure losses. You have to move this many CFM, or the numbers don’t come out right.  Exactly how much these items diminish your airflow depends on your exact configuration and is beyond the scope of this introductory article!

What to do when your outside temperatures are higher than your maximum allowed indoor garden temperatures:

You have a few choices:

1)    Stop growing for a while ’til things cool off, or try running your grow lamps at night when inlet air will be cooler.

2)    Reduce your lighting to drop the heat load. Not good if the incoming air is already over critical when it arrives in the box. Might be possible if the inlet air temperature is lower but you are running too many lights to keep up with the cooling.

3)    Use active air conditioning.

Any other helpful formulas out there? Tell us about it below!

The obvious heat-beating tactic is to install an air-conditioning system. But this just isn’t feasible or desirable for everyone. Other growers use air-cooled lighting to manage rising temperatures in their indoor gardens. After all, it’s your HID bulbs that generate the vast majority of heat – so it makes sense to tackle the problem at source.

Air-cooled lighting is not a complicated idea. The bulb is encased behind glass in a tube or reflector. Both styles have two holes at either side, one for air to be blown in and one for air to exit, taking heat with it. So, using an extractor and a few lengths of ducting, it’s pretty simple to create a stream of cool air, blown directly over the bulb, which constantly cools it. The hot air exiting the reflector is then ducted out of your indoor garden, minimizing its potential to heat up your growing environment.

Suck or Blow?

For best results, the cool air should be blown over the bulb, not sucked over it. There’s still a lot of debate in the indoor gardening community over this one – but one good reason is this: it’s better for the fan to blow cooler air through it, rather than “suck” hot air straight into it from around the lamp. You can also align two or three air-cooled lights in series using one fan and ducting in between lights – this technique is popular with growers using larger fans and reducers. It also makes for a lot less ducting and fan chaos! The cooler the air you can pass over your HID bulbs, the more heat it is able to remove. A properly air cooled light can remove up to 50% of the heat of the lamp. Some growers even go to the extent of passing air-conditioner-cooled air over their lamps (and not air-conditioning their indoor garden itself!).

However, air-cooled lighting isn’t just something that’s nice to have in the summer months – it allows you to position your lights closer to your plants all year round, meaning they can enjoy a greater light intensity. And more light on your plants = more yield. It’s as simple as that. Air-cooled lighting also reduces the cost of running a large air-conditioner. A cooler bulb results in less bulb stress and failures. It is much easier to remove heat at the source rather than try to get it after it has entered the indoor garden. Due to the small volume of air in the reflector (compared with the entire volume of the indoor garden), much less energy and effort is required to remove the same amount of heat.

As mentioned earlier, there are two types of air-cooled lights available: tubes and reflectors. Cool-tubes allow the grower to extract heat from the bulb completely without having to deal with the resistance of a larger, potentially more cumbersome reflector. However, the spread of light from a cool tube is smaller. Rectangular air-cooled reflectors usually come with a flip open glass lid beneath the lamp.

Some early air-cooled reflectors used low quality glass. Big mistake! The lower the quality glass, the more it absorbs light – light that your plants could be using. Make sure your air-cooled rig uses top quality glass. But even more importantly – KEEP IT CLEAN! Dirty, dusty glass can absorb more than 15% of the light from your lamps instead of it reaching your plants. Also remember: glass absorbs UV which can help with the production of essential oils in some crops (e.g. mint, basil and rosemary).

When ducting air from your air-cooled lights, make sure you use insulated ducting inside your indoor garden. This will help to prevent heat escaping through the ducting itself and thereby increase the efficiency of your cooling.

Finally, check how well sealed your air-cooled reflector is. An easy way to verify this is to switch on the fans that are cooling your reflector (and no other fans in the room) and light a match underneath it. Blow it out and watch the smoke. Does it get sucked up towards the reflector? Bad seal! Good seals are particularly important when you’re adding additional CO2 to your indoor garden as you don’t want it to be extracted through your lights before your plants have benefited.

Other bits and bobs you may need:

• Insulated ducting to match reflector and fan – 4″, 6″, 8″
• Duct clamps – 4″, 6″, 8″
• Inline fan
• Timer for fan (or fan could be plugged into the same timer used for light)

New Innovations: The Ice Box

Instead of ducting the hot air out of your indoor garden, check out “The Ice Box” by Hydro Innovations – it’s a specially designed heat-exchanger that fits on the exit-flange of your 6” air-cooled reflector. Using water at just 65 °F (18 °C), the manufacturers claim that it can remove all the heat from a 1000 watt lamp! Pretty damned impressive, and no ducting overload in your indoor garden!