Grow Room Setup

The initial grow room setup is certainly one of the most important steps for anyone to successfully grow cannabis indoors. An adequate grow room is one where there is a controlled environment tailored to suit the needs of your particular strain of cannabis plant. There are various factors, in which you need to consider for your grow room setup in order to optimise overall potential.


You will need to have an idea of how many plants you wish to grow in order to accurately calculate the amount of room and light you will need for your grow room setup. The size of the grow room and the amount of light that is correctly used are the two factors which determine the overall yield of a cannabis grow cycle. A 600 watt HPS light used correctly over a 4ft x 4ft space (1.2m2) should produce 15-20 ounces of good quality cannabis. HPS lights produce a vast amount of heat so ideally your grow room setup would be approximately 2 metres high, this is allows room for the fan and filter to extract rising hot air from the lights more efficiently. You will need to consider where you will position grow equipment such as inline fans and oscillating fans, a carbon filter and any other accessories you might be using. Lamps of different powers need different amounts of space in order to be used at their full potential, for example, a 400 watt lamp will cover a 3x3(ft) pace, a 600watt lamp will cover a 4x4(ft) space and a 1000watt lamp will cover a 5x5(ft) space. Click here for light positioning information.


Ability to maintain the temperature inside the grow room should be considered when choosing the location of your plants. You will need to take into consideration whether you will be able to keep it warm enough or cool enough, whether anyone will able to hear the sound of the fans, air conditioning or any other equipment you may be using. Where will you get your fresh air from? Where will you ventilate your used air to? Can you get an easy and sufficient supply of water and electricity to this location? I would recommend setting up your grow room in a private place that isn’t often visited. For example a grow room setup where there is a boiler, may seem ideal at the time but if it breaks and needs to be repaired it would mean dismantling your grow room setup.

Security and secrecy.

Essentially, for your plants to reach their full potential you will need a high quality carbon filter and a ventilation system that creates negative pressure to avoid any unwanted odours escaping the grow room setup. Although you will be using a carbon filter, some odour may still occur with little ventilation. I would recommend that you avoid extracting hot air into an unventilated place as this will cause windows to condensate, an obvious sign of a cannabis grow.

The sound of cannabis growing equipment can be quite distinctive and therefore noticeable, particularly to experienced cannabis growers or anyone who has heard the sound of a grow room setup previously. I would recommend that you consider spending a little extra money on quieter equipment, hanging fans from bungee cords and a fan silencer can make a big difference to the level of noise.

Controlling Air Flow

A tightly sealed grow room is always more effective. The only way that air should flow through the room is via the intake and extractor fans. The intake fan should be positioned near to the floor to bring in fresh air and the extractor fan, with the carbon filter attached, should be placed near the ceiling on the opposing side of the room. The fresh air will enter the room at a low level and be circulated via the intake fan, the air will then become warm and rise up towards the ceiling and as a result the extractor fan will work effectively with a constant supply of used air, creating a very efficient air flow.

It is important to remember that you’re extraction fan with carbon filter attached will need to exceed the power of you’re intake fan to create negative pressure in the room, this ensures that all of the odorous air flows through the filter without escaping. Fan speed controllers can be used to ensure that the rate of airflow and temperature of the room is kept stable at all times, you will also need a thermometer in the room in order to show you the temperature allowing you to access whether you need to make alterations. An oscillating fan should be pointed in the gap between the light and the top of the plants, i would suggest you buy on that’s adjustable in height or alternatively, hang it from a hook and string upside down so that you can shorten the string to raise the height of the fan or vice versa, should you need to.


Health & Safety

When setting up an indoor grow room its likley that you may need to wire a plug or fan yourself, if you are inexperienced at this, don’t worry, there are plenty online guides to assist you on google search, or you could use the instructions that came with your fan as a guide. When using an extension lead, always remember to check that you are using the correct cable for the amount of power you wish to supply.

You should place plugs, timers and ballasts outside of the room, but all of the these things should be elevated from the ground incase of a flood. If possible i would recommend you line your floor and bottom of the walls with plastic sheeting so that in the unfortunate event of a flood the sheeting acts as a bath to stop the water escaping and causing further damage. You can also place your ballasts on house bricks and attach the plugs and timers ect to a board or wall to protect them.

Organising The Room

Taking the time to plan and construct a well organised grow room will essentially create far less stress for you in the future. Simple things such as placing cables out of the way, having a pre-organised method of raising and lowering lights and allowing yourself space to store tools and mix nutrients will make things much easier for you and give you more time to concentrate on your plants. If you plan to build a grow room in a loft with reflective grow sheets, a stapler and tape, please remember to place a doorway into the room where you can access plants easily to work on them. If you plan on building your own grow room from reflective sheeting i would advise you to staple the sheet into wood then tape over it an staple through the tape, as general use of the room (wear and tear) and enough negative pressure from fans can cause the sheet to easily rip.


The room you are using should be both light and air sealed, any light that leaks into the grow from outside the room can cause confusion to the plants affecting their growth potential. If your any of your equipment emits light such as a heater with a red ‘on’ light I would suggest that you tape over it. On the inside of the room you should be using reflective white paint or some form of reflective sheeting if you wan’t to get good results for your money as this will optimise your light emittance. The lights should be adjustable in height so that you can always have them at the desired distance from the plants.

Useful hints and tips!

400 watt lamp will cover a 3x3(ft) pace. A 600 watt lamp will cover a 4x4(ft) space. A 1000 watt lamp will cover a 5x5(ft) space.

400 watt lamp should be kept 30cm(1 foot) away from the plants canopy. A 600 watt lamp should be kept 45cm(1.5 foot) away from the plants canopy. A 1000 watt lamp should be kept 60cm(2 foot) away from the plants canopy.

A useful method to ensure the distance from light to plants is sufficient is by putting the back of your hand underneath the lamp for 30 seconds, if it’s too hot for your hand it’s too hot for the plants. Click here for more on this.

While the lights are on the room temperature should be 25-27ºC, while the lights are off the room should be 20-22ºC.

The grow room will need 1 medium sized oscillating fan(around 12-16 inch) for every 2 lights used, the fan should blow in the gap between the lights and the plants canopy, do not blow a strong wind directly at the plant as this will cause the leaves to dry out and hinder growth.

An intake fan and an exhaust fan with enough power to completely exchange all the air in the room within 5 minutes. A 5 or 6 inch exhaust fan(depending on model and heat being produced) per 2 meters squared(2 400 or 600 watt lights) with a suitable intake is usually adequate.

It is important that your exhaust fan with a carbon filter connected can move more air than your intake fan to create a negative pressure in the grow room. If the intake fan brings in more air than the exhaust can take out you will 100% have issues with the smell of weed escaping the room for anyone and everyone to sniff out. A carbon filter will reduce the amount of air a fan can move by 30%, take this into account when measuring the CFM ratings of the 2 fans. A fan speed controller can be used to ensure the correct temperature and a negative pressure is maintained. I advise you to spend a little extra money on a good quality carbon filter as a cheap budget filter will not fully clean the air that passes through it, this is especially important in the flowering stage as the odours given off by maturing cannabis buds are extremely strong and distinctive.