Ventilation Explained

[dragonboizee]

nice one mate, you dont know how much you jus helped me with this post i bn scratchin my head about this. thanks again. top man.

[Adambomb]

exactly the info i needed ,have now set my cf and fans with confidence superb timing of a superb post!

[a13x]

something i found on the topic

Below are two ways you can work out the size of extractor fans you will need in your grow room.

1. This method is based on the volume of the grow area and is perfectly suitable for small grow rooms.

First calculate the size of the room in cubic meters (m3): Length x Width x Height in meters = size of room in cubic meters.

Then multiply the total m3 by 25 to give you the air exchange needed in one hour.

Add 30% to this figure to allow for the inefficiency created by using carbon filters and lengths of ducting and the figure you will have is the air exchange rate needed in m3/hour for your grow area.

Because all extractors are sold with a m3/hour air exchange rate, it is a simple matter to select the correct size fan(s) you will need. For example, if you have calculated the air exchange rate needed is 450m3/hour then this could be achieved by using one exhaust fan rated to 450m3/hour or by using two fans, one for input and one for exhaust that together total this amount. If you use two fans (recommended) make sure that the exhaust fan is approximately 70% larger than the input fan.

2. This formula is used by commercial growers and is based on the number of lights used. This is recommended for medium to large sized grow rooms and guarantees the control of temperature regardless of the number of lights being used.

Extraction:

Take into account at least 200m3 of exhaust for each 400w lamp
Take into account at least 300m3 of exhaust for each 600w lamp

Add approximately 30% more exhaust to this to allow for the inefficiency created by carbon filters and lengths of ducting.

Intake:

Intake should be approximately one third to one half of the volume of the exhaust. (If your extractor is 1000m3 per hour or less, use approximately one third of its volume for input. if your extractor is over 1000m3 per hour, use one half of its volume as input)

Example 1: A grow room with 5 x 600w lamps would be 5 x 300m3 = 1500m3 of exhaust. Add around 30% to this (approx 500m3), and you will need 2000m3 of extraction. The size of the intake fan should be approximately half of this, so about 1000m3.

Example 2: A grow room with 2 x 600w lamps would be 2 x 300m3 = 600m3 of exhaust. Add around 30% to this (approx 180m3), and you will need 780m3 of extraction. The size of the intake fan should be approximately one third of this, so about 260m3.

Hot air rises so your exhaust fan should be situated at the highest point of the grow room and the intake should be situated at the lowest, most opposite point. Air should come in from below and make its journey up through the grow room and through the plants, supplying them with what they need. The air then moves out through the extraction from above taking away with it excess temperature and humidity. You must be careful to avoid what is known as a ‘laminar flow,’ this is where air is drawn in through one vent and out through another without moving through the plants. You may find it helpful to imagine that you can see the air flow as little arrows making their journey through the room. There should be no stagnant areas in the room, the air should always be moving. Oscillating fans are essential to move the air around as it makes it journey. Take care not to bash plants around with oscillating fans; the idea is to move the air around the plants rather than moving the plants themselves. When you look into your grow room you should see the leaves gently shimmering as the air moves through them. They should not look like they are in force 9 gales.

It is advisable to have a separate intake fan although you can use a passive inlet. This needs to be a vent hole at least the same size as the size of the extractor you are using to draw air out of the room, for example, if you are using a 200mm extractor then the size of the inlet hole should be at least 200mm. This can be one hole or several providing the total open area equals at least 200mm. In practice we recommend the inlet hole to be approximately 20% larger than the exhaust, this reduces drag and allows the extractor to work more efficiently. Providing that the rest of the room is sealed, the volume of air the extractor is pulling out will now be pulled in through the passive inlet.

A separate intake fan that is one third to one half of the volume of the extraction fan is much more efficient and is what we recommend. It allows better control of temperature and humidity, creates a negative air pressure within the room that is good for plants and prevents smells escaping back through the ventilation system, and because the extractors are not working so hard you will find they makes less noise and last longer. Also the size of the hole needed to fit an input fan into the room needn’t be as large if using a passive inlet.

[Mr_Bimble]

How do I work out the amount of ventilation I have is enough for this setup as I'm planning on setting it up at a friends in a couple of weeks?

Small tent 60*60*100 with a 6400K 250W CFL running 18/6 for Veg it has a passive inlet from an unheated loft, the outlet of this tent is fed into the inlet of a larger tent using 5" ducting, the larger tent is 100*100*160 with a 250W HPS running 12/12 for flower.

Planned extraction is via a 5" Rhino carbon filter & 5" RVK running full speed 24/7 in the large tent with acoustic ducting and an exhaust silencer.

Do I just add the volumes of the two tents, multiply by 25 & add 30% for the loss caused by the filter? ie ((0.60*0.60*1.00) + (1.00*1.00*1.60) * 25) * 1.30.

[Naxx]

a 5" extraction and passive intake will be fine for a cfl, and should be ok with the hps

[BudMan]

a 5" extraction and passive intake will be fine for a cfl, and should be ok with the hps

Id think 4" would be better for in loft... Be cold up there to begin with

[a13x]

the origional post is wrong i think as if you calculate the fan needed for 1 600w hps light you would use a space of 1m x1m x2m or 1.2mx1.2mx2m or something symilar, if you calculate it using the first post youll get the power of a smaller fan i think its common knowledge that to adequetley ventilate a 600w hps in that space you need a 6" extraction and 4" intake. if you follow the 2nd method on my above post youll find that the result will be a 6" extraction. the 1st method in my above post is flawed because it doesnt take into account the lamps and it uses the maximum reccomended air circulations per hour.

[stone14]

ok so going off weed lovers post for calculating fan size a 2.4mx2mx2m with 8x600watt hids and 2cfs a 12" ruck etaline fan (3490m3h) exhaust and a 10" ruck etaline fan (1750m3h) intake is fine with 2x12" cfs will be ok

[Sparky30g]

Air Circulation

Always provide your plants with adequate air movement and circulation in the grow room. Air circulation within the room eliminates stale spots and also reduces the formation of micro-climates within the leaf canopy. If air circulation in the grow room is poor then the micro-climate in between the plants increases in humidity and temperature. This can result in mildew and insect problems, as well as less deficiencies. For adequate air circulation use a wall mounted fan; 2-3 fans will provide sufficient air movement. Never switch these fans off unless you are spraying or fogging your room[/QUOTE]

[121beale121]

NAXX i have built a room myself 1.2wx2.4lx2.2h its basically half of a small room what intact and outtake should i have? also with me having such a long room my intake by the window of fresh im thinking of ducting all along the back wall and stabbing it up so it leaks oxy out all by the bottoms of the plants what do you reckon mate, really looking forward to your answer