250 watt hps heat?

ok if anyone has something to help me out please dont hesitate to offer your thoughts if you have been there done that i really would like your help..im going to be running my 250 watt hps with 4x 2700k 23 watt cfl for full spectrum in flowering my question is im going with 2x 6" inline fans for exaust one to each upper side of box what type of intake should i run for best results?should i do a passive intake for this set up or should i run a couple of 4" fans bottom side to assist with the intake? my box is 2x3x3 1/2 depth width hight i have 2 x 6" circulating fans inside for air flow...any help is apreciated..thanks and peace pot prosperity

As long as you have a vent at the bottom to let in cold air, if you have a fan that is pushing air out then there will be a negative pressure in the box and suck air in. Its good enough with the 2 6" fans unless your temps are going above 30 degree Celsius or 86 Fahrenheit then you might want to add one for intake.

yeah thats what i tried with my current cfl grow and when i sealed my box the temps got way to high then i had 1x 4" 80cfm exaust fan at the top and 2x 1 1/2 " passive intake holes in the bottom...maybe the exaust and intake were not large enough thats why im looking for some kind of ratio intake to exaust.. thanks for your reply...ppp

anymore help would really apreciate it from anyone..

I am not sure if this helps.
Here’s how you can calculate the amount of ventilation you need. If for instance you wanted to keep you grow room temperature from getting any more than 5° warmer than the intake air temperature, and you were using 400 watts of power, you’d make the calculation below in blue. The chart is based on the following formula. It is a well-established heat transfer formula.


(3.2 × 400) ÷ 5 = 256

---------------------------Calculating the passive intake.-------------------------

The Home Ventilating Institute recommends one square foot of open air inlet per 300 CFM of ventilation fan capacity.

If you were going to use 256 CFM, you’d want 256/300 square feet of intake area, which is 122.88 square inches.

Here are some options for the intake area for a 256 CFM ventilation fan:

1 hole - 12.5 inches in diameter.
2 holes – 8.84 inches in diameter.
3 holes – 7.22 inches in diameter.
4 holes – 6.25 inches in diameter.
5 holes – 5.59 inches in diameter.
6 holes – 5.11 inches in diameter.


Here is how to calculate the hole sizes:

1. Take the total area in square inches needed, in this case 122.88 square inches, and divide by the number of holes you want.
2. Then divide by Pi (3.14).
3. Take the square root of that value.
4. Then multiply by 2.

The answer is the diameter that each hole would need to be to make up the total area needed for intake.

A large number of small holes will create more backpressure than one large hole of equivalent area. This would be negligible unless you’re using a huge number of holes or you’re using ducting to supply the air to each intake hole. If you’re just cutting them in a wall you should be fine using 8 or less holes without having to take into account the extra backpressure.

What is the CFM on the 6 inch and proposed 4 inch? Air pressure is tricky when you decide to add intake fans. It has to be very close to balanced. For that size area depending on CFM of the 2 six inch fans a 12 inch passive intake should be fine.

Edit: FMan do you play L2?...sry but had to ask

Fman said:

I am not sure if this helps.
Here’s how you can calculate the amount of ventilation you need. If for instance you wanted to keep you grow room temperature from getting any more than 5° warmer than the intake air temperature, and you were using 400 watts of power, you’d make the calculation below in blue. The chart is based on the following formula. It is a well-established heat transfer formula.

(3.2 × 400) ÷ 5 = 256

---------------------------Calculating the passive intake.-------------------------

The Home Ventilating Institute recommends one square foot of open air inlet per 300 CFM of ventilation fan capacity.

If you were going to use 256 CFM, you’d want 256/300 square feet of intake area, which is 122.88 square inches.

Here are some options for the intake area for a 256 CFM ventilation fan:

1 hole - 12.5 inches in diameter.
2 holes – 8.84 inches in diameter.
3 holes – 7.22 inches in diameter.
4 holes – 6.25 inches in diameter.
5 holes – 5.59 inches in diameter.
6 holes – 5.11 inches in diameter.


Here is how to calculate the hole sizes:

1. Take the total area in square inches needed, in this case 122.88 square inches, and divide by the number of holes you want.
2. Then divide by Pi (3.14).
3. Take the square root of that value.
4. Then multiply by 2.

The answer is the diameter that each hole would need to be to make up the total area needed for intake.

A large number of small holes will create more backpressure than one large hole of equivalent area. This would be negligible unless you’re using a huge number of holes or you’re using ducting to supply the air to each intake hole. If you’re just cutting them in a wall you should be fine using 8 or less holes without having to take into account the extra backpressure.

Click to expand...

hey man thanks thats what ive been looking for something solid im kind of technical almost anal about it when you start purchaceing high price beans lol thanks to you + rep my man...

Dradden said:

What is the CFM on the 6 inch and proposed 4 inch? Air pressure is tricky when you decide to add intake fans. It has to be very close to balanced. For that size area depending on CFM of the 2 six inch fans a 12 inch passive intake should be fine.hey dradden they are 150 cfm rated each and the 4 inch intake is 80 cfm's rated so your saying of i run a passive intake and my two exaust are 320 cfm = 12"total my passive should be almost equal say 10" or so..? also ill be using one strictly for cooling the light and the other for cab exaust..

Edit: FMan do you play L2?...sry but had to ask

Click to expand...