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How To Build Your Own Hydroponics Grow Room – Dialing In Your Temperature and Humidity (part 3)

In this new, exclusive series from Advanced Nutrients we show you to build your own indoor hydroponic garden so you can start enjoying the benefits of growing!

How To Build Your Own Grow Room Series:

Part 1 — Choosing your space & planning
Part 2 — Calculating lighting and insulation needs
Part 3 — Dialing in your temperature & humidity (you are here!)
Part 4 — Accurately calculating heat, plus safety & sanitation tips

In part one we covered how to choose the perfect spot for your grow room, including many factors that you needed to keep in mind to set you up for success.

In part two, we went over calculating the lighting you need and insulating your grow room.

Today, we’re going to talk about organizing your grow room and dialing in your environmental needs such as temperature and humidity!

The Importance of Proper Ventilation In Your Grow Room

There are many reasons why a proper ventilation system is super important for your grow room.

Here are just a few …

  1. Faster Growth and Bigger Yields! Plants given the right environment grow faster and produce more buds/flowers.
  2. Maintains Ideal Temperature and Humidity! A properly setup ventilation system helps control the temperature & humidity levels in the grow area by venting out hot and humid air, and replacing it with fresh air. Fans within the grow area prevent hot or humid patches.
  3. Helps Prevent Mold & Pests! Many molds and pests like stagnant air, high humidity and heat. Fresh cool air blowing over and under your plants will reduce your chance of seeing many types of mold and pests.
  4. You Get Stronger Stems! A breezy environment strengthens stems because the plants are forced to grow stronger, just like they would in nature


Proper ventilation is also important because it keeps your grow room in the ideal temperature and humidity range

What Is The Ideal Humidity And Temperature?

There is some debate to this, but here are some good guidelines …

When your lights are on:

The ideal temperature for cuttings & seedlings is between 68ºF and 77ºF (20ºC and 25ºC). For both, you can start around 60-70% humidity and gradually reduce it to around 40% humidity as your plants mature …

That’s because as the plants go through vegetation and bloom phase, they can evaporate more & the temperature may increase to a maximum of 82ºF (28ºC).

What’s important though is to gradually reduce the humidity as the plants get more mature too.

If you’re starting around 60-70% humidity it should gradually reduce to 40% humidity by the time you’re ready to harvest.

Here is a typical “ideal” level of humidity as your plants grow, flower and are proceed to harvest.

Week 1 growth: 60%-70%
Week 2 growth: 60%-70%
Week 1 flower: 55%-65%
Week 2 flower: 50%-60%
Week 3 flower: 50%-55%
Week 4 flower: 50%-
Week 5 flower: 50%
Week 6 flower: 45%
Week 7 flower: 45%
Week 8 flower: 40%
Week 9 flower: 40%

When the lights are off:

The temperature should be between 62ºF and 72ºF (17ºC and 22ºC). (Humidity levels should remain as when the lights are on).

BIG TIP: Another important guideline that expert growers follow is to keep the temperature differences between day and night as little as possible — a maximum difference of 10ºC is ideal. In other words, if it’s 82ºF (28ºC) during the day, you don’t want it to drop below 64ºF (18ºF) at night. In fact, most growers agree that a temperature difference of only 5ºC is ideal.

How To Calculate How Many Fans You Need

In the video below, expert grower Eljay again helps us figure out how many fans we need for our grow room.

Once we know how many lights we have, we can start to get an idea of our ventilation needs.

To cool lights properly, you should use about 150 – 250 CFM per light.

What is “CFM” and why is it important to hydro growers? Most fans purchased at your local hydroponic dealer are rated by their CFM. This stands for Cubic Feet per Minute and dictates how many cubic feet of air this fan is capable of moving per minute.

For example, let’s say I was building a grow room using 6 lights. That means that if I am trying to hit a target of 200 CFM per light then I would multiply my 6 lights times 200 CFM and arrive at the number 1200. This is how much CFM I should be using to cool these lights.

Normally you would use a 12 – 14 inch fan to get an output that high, then we would reduce the ductwork down to the size of your reflectors. But in this case, you could easily use two 8 inch fans that are 630 CFM a piece.

BIG TIP: Many experienced growers like to use one fan on the intake that feeds the lights, and one fan on the exhaust that helps pull the air through quickly. That way you’re still using over 1200 CFM of fan, but you can’t add two fans CFM together, it doesn’t work like that. This system just runs at a very strong 630 CFM. However, either way will work.

How To Figure Out Your Air Cooling Needs…

Now there are two ways to cool your grow room that most growers use …

You can either go straight against the heat you are generating with Air Conditioning or you can use fans and Air Cool your room.

Method #1: Air Cooling your Room – How To Cool & Ventilate Using Only Fans

Again, expert grower Eljay helps us here, to explain how to use fans to cool your grow room …



When you’re using “Air Cooling”, you’re using fans to pull cold air from outside into your room, and exhaust the heated air from inside your grow room.

Remember, you’re trying to mimic outdoor temperatures inside of your room. The target for this is to clear the cubic footage of your grow room in 1 – 2 minutes.

The faster you can exhaust all of the cubic footage of air from inside your room, the better that this will work. The idea is to replace the heated air from within your grow room with colder air from outside.If you are going to air cool your room then additional venting will be required.

The good news is this is a much cheaper method than air conditioning, both for the initial purchase and monthly usage (generally). This method works best with colder outdoor temperatures, however if you run your room at night you can use this method in most areas. You are looking for temperatures below 70 degrees before this is an option worth exploring.

The downside of this method is that you can’t inject CO2 because you are removing all of the air from the room every minute or so. By doing this you would be theoretically exhausting all of the CO2 out of your room as well.

This method does NOT require a lot of math which makes it GREAT for beginners — if the room is hot, cycle more air faster!

The only math required is taking your cubic footage of your room and matching it up to the cubic footage of the fan or fans you will be using.

To do this we need to figure out our square footage of our room and then multiply it by the height of our room. For example if I have a 12ft by 7.5ft grow room, then the math looks like this: 12ft x 7.5ft = 90 sq. ft. And if my ceilings are 9ft tall, then I multiply 90 sq. ft x 9 ft. tall = 810 cubic ft.

Knowing that I have 810 cubic ft. I will start by using 747 CFM fans for intake and exhaust to see if that will cool the room amply. The fans will be clearing the room in about 1 min 10 seconds. If this doesn’t work, I add more or bigger fans!

It’s that simple and for that reason, it’s our #1 choice for beginners to cool their grow room!

Method #1: Air Conditioning your Room: What You Need To Know

In this video, expert grower Eljay shows us the ins and outs of air conditioning for our grow room …



In order to calculate the amount of Air Conditioning we will need, we will be learning about BTU. BTU stands for “British Thermal Unit”. This is how most of the world measures heaters and air conditioners.

Some of you might be asking “How much heat does a 1000 watt bulb put off?”

A lot of experts say that HPS bulbs put off around 3.5 to 4.0 BTU per watt. Meaning that a 1000 watt bulb will generate 3500 – 4000 BTU. Now the thing to keep in mind here is that 3500 – 4000 BTU per 1000 watt bulb is for an un-air cooled bulb. This would be the heat you are going up against only when using parabolic reflectors or just hanging vertical lights from a socket with no air cooling in your reflector.

Air cooling will generally remove around 25% – 50% of the heat generated. The reason for the mixed results has to do with your air source. That means that if you are pulling air from outside in Oakland, CA at night you can expect that air to probably be around 40 – 50 degrees. If you are pulling air in the middle of a summer day in Palm Springs, CA that air can be over 100 degrees, and not a lot of cooling will take place. Once again, this is another benefit to running your grow room at night and drawing cold air from outside.

Maybe you have purchased an air conditioner in the past and noticed that it said 12,000 BTU or 8,000 BTU. This is the amount of cooling that the air conditioner is capable of putting out. 12,000 BTU is also called 1 ton of cooling. Meaning that a 5 ton air conditioner puts out 60,000 BTU. And a 1 ton air conditioner puts out 12,000 BTU. These BTU ratings are critical when trying to cool your room. Let me give you an example.

If you had 4 x 1000 watt air cooled lights in your grow room, and you were in taking cold 40 degree air from outside you could expect probably a 40 – 50 percent reduction in heat per light, meaning that 4 lights x 4000 BTU would be 16,000 BTU. Once we air cool them properly we could safely reduce that 16k BTU of heat by 40% resulting in 9600 BTU of heat that we are actually going up against with air conditioning. This means that a 1 ton “12k BTU” Air Conditioner should amply cool this area.

Wrapping It All Up…

At this point, we’re almost done!

You discovered the ideal environmental conditions in your grow room and how many growers typically achieve this … the types of cooling systems they use … and more.

In the next installment of this series we will cover:

  • How to calculate EXACTLY how much heat you’ll have in your grow room
  • 5 safety & sanitation tips you absolutely MUST know
  • And much, much more!


Until next time, please share this article with your friends or anyone you think it can help. Post it to social networks too. And good luck finding the perfect grow room space!


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About the Author

The Advanced Nutrients Team

Since 1999, Advanced Nutrients has been committed to educating the community and bringing the most up-to-date knowledge to the forefront of grows across the globe. Every article you read here has been curated by Advanced Nutrients’ industry experts, so you can continue raising your bud weight… and your reputation.

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Over time, components within the nutrients settle on the bottom of the bottle. When you pour a bottle without shaking it, you can potentially be pouring out an unbalanced solution. Shaking up the nutrient bottle ensures you are pouring the right blend into your reservoir, giving your crops the nutrition they need.

Usually, it’s not a problem. But some products are incompatible with each other and can damage your plants when they’re used together. For example, bloom boosters with high PK numbers or low-grade silica products can destabilize your nutrient mix and cause nutrient lockout.

Nutrient manufacturers design their products to be used with each other. In doing so, they include specific portions of each nutrient in each product, so crops receive the right nutrition through each stage of the grow cycle. When you stick with one manufacturer, you don’t have to worry about inadvertently destabilizing your nutrient mixture. One example of why you need to stick with only one manufacturer’s products is Advanced Nutrients’ pH Perfect line. These products are designed to keep your crops’ root zone within a specific pH range. When you use them alongside products from another manufacturer, we can’t guarantee your root zone will maintain its optimal pH level.

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