Setting for another indoor round! Need advice

[DSXJ]

Hey Guys, finally have a little room to go indoor again.

Will be my second log on this forum as my outdoor crop comes to a finish soon.

Tent :
4' x 2' x 5'

Lighting :
600w HPS/MH w/ Cool tube

Soil :
SeaSoil -- Giving this a shot after I have heard great reviews.

Nutrients :
Fox Farm line w/ additives like calmag.

Strain :
GHS Super Critical ( BB x WW x Skunk )

I can only do 1 grow a year and would like to make it the most beneficial. Looking for atleast 1lb.

Plan of attack :

SCROG
I will be scrogging these girls with the screen 8" above medium (2"x2" holes for screen). I will be using the defoliation technique as well between week 2 and 3 of flower.

Questions :

1. How much CFM will I need to circulate air properly? ( I plan on using 2 homemade carbon filters, and 1 blowing fan for the cooltube. )

2. Given the above information, do you think it is possible to pull atleast 1lb out of 4-6 plants with 6 weeks of veg?

In the past I have pulled 3/4 of a lb off 5 plants and a 400watt light with very poor soil and walmart nutrients, on a 4 week veg.

Any information is appreciated, thanks!!

 

[JJ Bones]

A simple 4" duct fan should work well enough for that space: Ideal-Air Inline Duct Booster 4in 70CFM

 

[DSXJ]

A simple 4" duct fan should work well enough for that space: Ideal-Air Inline Duct Booster 4in 70CFM

Thanks for the reply.

I'm going to be using 6" since the port sizes on my tent are for 6". Not sure if you can still use a 4" fan since it's my first tent and I have not received it yet, going under the assumption they only fit 6".

I'll use 3x 70cfm fans and that should be plenty until I get into winter in a few months then my temps will drop significantly and I can probably get away with just 2 for the carbon filters and use the lights heat to keep the room warm.

Thanks!

 

[JJ Bones]

Try to get a fan controller as a 6" fan will likely be way too powerful for that size grow tent.

The vent ports can be tightened down to accommodate other fan sizes.

 

[DSXJ]

I'll take your advice and get some 4" 70cfm fans. I want to run 2 exhaust atleast for 2 carbon filters since the smell is going to be pretty strong.

Thanks boss!

 

[shottafire]

For that space I would use a 6" inline still but i would cool the light and have my filter on the other side of the light, so you would be exhausting and scrubbing the air with one fan. A speed controller is a nice extra to have around and you can use it to control the amount of flow you need. Two carbon filters for that space is completely unnecessary and not sure how it would fit in there with everything else.

 

[DSXJ]

For that space I would use a 6" inline still but i would cool the light and have my filter on the other side of the light, so you would be exhausting and scrubbing the air with one fan. A speed controller is a nice extra to have around and you can use it to control the amount of flow you need. Two carbon filters for that space is completely unnecessary and not sure how it would fit in there with everything else.

Gotcha, I'll use a 6" inline for fan cooling & carbon exhaust.

Dont think I'm gonna bother with the speed controller.

Also I dont think the heat is going to effect me majorly because in winter it can get to -40 easily. The first few months will only be -10/-20 or so. Wich the light should provide some nice heat for the house and my room

Thanks guys -- 2 1/2 more weeks till journals up!

 

[shottafire]

If its that cold you may want to just have a fan connected to your filter and forget exhausting the light. I have never grown in such a cold climate so What I told you might work it might not.

But you will be able to figure it out with everything you have.

 

[GreatLife4All]

Since you are, in essence, trying to vent a greenhouse, let me give you some data from one of my books.

These numbers are based on emperical research in outdoor greenhouses in full sun at the hottest point of the day. Therefore, these will be sufficient for all but the most intensive lighting systems.

The first column is the amount of air that must be moved from outside to inside to cause a temperature drop whose range is given in the second column. There are issues with this table, but I have found it very helpful in setting up my tents.

Air Change Rate,	Inside Temperature,
Volumes/Minute	Degrees F Above Outside
1/2	16 to 18
3/4	11 to 13
1	8 to 10
2	4 to 6

So lets make some assumptions and see where this table leads us.

A1 - Indoor Temp Goal 75F

A2 - Outdoor Temp Range 68-72

A3 - Tent Size 4x4x6'
​

Based on our assumptions, we know that we are trying to ventilate a space of 96 cubic feet (4' x 4' x 6').

We also know that we want to maintain a 3 to 7 degree temperature differential between inside the tent and outside the tent. So lets look that up in the table above... and we see that it is close to the same range for the last row in the table. So we need to change the air somewhere around 2 x each minute in order to effect the desired temperature drop.

So lets round a little and say that we need a fan that runs at 200 CFM (100 CF x 2 cycles/min).

but you will find that this is not sufficient. Why? Because you will NEVER get the rated capacity out of a fan once you attach it into your system. The numbers that I used above are taken from measuring the exhaust coming out of the greenhouse - not the rated capabilities of the motors. And this makes a difference.

In theory, you can use the type of duct work, the length of duct, the number of corners, to calculate the loss of air flow. In general, more flexible duct has greater loss than rigid... longer runs have greater loss than shorter... and the more corners you put in the more flow you lose (and this is a BIG loss). So you want to design your ventilation to run as short and straight as possible.

So... to make things simple. I just double what I need and keep all the duct work as short and straight as possible. Seems to be a pretty good metric that works in practice.

So... for a 4 x 4 x 6' tent, running a 1,000W light, you will need a 400CFM fan. Add 10% for errors... and both of my tents actually have 440CFM fans. I have had no issues with mold or humidity.

You can run this same math for your tent size and get a very good estimate for what you will need. A 600W light will not heat the tent as much as a 1,000... but more than a 400. So you will need to adjust slightly if you are running less than 1,000W. But if you just run the numbers like I did and stay below 1,000W - you will have more than enough.