400w hps too much for this homebox?

(inch):31 1/2 x 31 1/2 x 63

Not if you move enough air through it.

air cooled relector ???

The light is perfectly fine to use in that box assuming you can control Temp still. An air cooled reflector would be ideal but it can be done without it. Do you have a passive intake or are you using a seperate fan for exhaust and intake?

jealous wish i had one

I have a 95 CFM fan exhausting. It most likely won't be air cooled, but this fan is overpowered for this box so I should be good Im thinking?

Thanks guys...and how the hell do I leave rep?

whats your temp, looks like mh is it? my journal might help setting up your tent. might want to get a 6 in inline

Toppers said:

I have a 95 CFM fan exhausting. It most likely won't be air cooled, but this fan is overpowered for this box so I should be good Im thinking?

Thanks guys...and how the hell do I leave rep?

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You will be needing to move more air about 250+ CFM without an air cooled hood. How are you intaking air that is important as well. You will surley want to have a small oscilating fan inside there to stir up the air as well.

A cheap fix for you without having to buy an inline fan is to use a Dayton 6" or 4" Axial Fan. Tape it to ducting on both sides directing air where you wish. The 6" moves an Impressive 230+ cfm and can be bought for about 75 bucks uses only 27 watts! Intake air passivley and keep a small oscilating fan inside to stir air and you will be good. This is what I would do. G/L.

I haven't bought it yet. Its going to be a 400 hps for flowering. And yes its passive thru my 95 CFM.

DDub said:

You will be needing to move more air about 250+ CFM without an air cooled hood.

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Where are you getting this? My fan is too much power for this small space as is.

Toppers said:

Where are you getting this? My fan is too much power for this small space as is.

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This is how you can calculate the amount of ventilation you need. If 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.


CFM= 3.2 x Wattage/ Difference in Degrees Farenheit from Intake Air

So, (3.2 x 400)/5 = 256 cfm


I don't know where you are getting that 95 cfm is overpowered....

DDub said:

This is how you can calculate the amount of ventilation you need. If 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.


CFM= 3.2 x Wattage/ Difference in Degrees Farenheit from Intake Air

So, (3.2 x 400)/5 = 256 cfm


I don't know where you are getting that 95 cfm is overpowered....

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Ok cool thanks. Well, 5.25' x 2.5 x 2.5 = I need a 32 cfm fan...am i doing this wrong?

Toppers said:

Ok cool thanks. Well, 5.25' x 2.5 x 2.5 = I need a 32 cfm fan...am i doing this wrong?

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Yes you are doing this wrong. First of all this calculation has nothing to do with the size of the room. Answer me this and I will tell you what size fan you need. What is the temperature (in Farenheit) of the room that your Homebox is in.

DDub said:

Yes you are doing this wrong. First of all this has calculation has nothing to do with the size of the room. Answer me this and I will tell you what size fan you need. What is the temperature (in Farenheit) of the room that your Homebox is in.

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So how do I calculate it right? And I'm talking about what size fan I need to get air exchange on my grow, not for cooling this light.

Temp is 70 now, it's wintertime here. Probably 75 in spring/summer.

Toppers said:

So how do I calculate it right? And I'm talking about what size fan I need to get air exchange on my grow, not for cooling this light.

Temp is 70 now, it's wintertime here. Probably 75 in spring/summer.

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Ok so if Temp in room is 70 right now the calculation I made in the post above is exactly what you need to exhaust this grow area, not the light.

The calcualtion I made above would keep your temp in the Homebox at about 75 Farenheit now and 80 Farenheit in summer, 80 is too warm. You need at least 250+ CFM just like I said at first.

I'll try to explain this Formula: ****FORMULA APPLIES TO MH/HPS ONLY NOT CFL****

3.2 x W/T = CFM

( 3.2 is the only constant in this formula )

W= Watts of Light
T= Temp. increase from Room Temp.
CFM = Fan strength required

3.2 x (Watts) / (The Temp in degrees Farenheit Air will increase from Room Temp.) = Your required CFM's to keep Temp at Normal Room Temp plus (T)

So again in your case:

3.2 x 400watts= 1280
1280/5 ( 5 because you don't want Temp over 75 degrees Farenheit and you starting room Temp. is 70, so 70 + 5 ) You can substitute 5 with any number but this will be the increase from normal room temp.

So lets say we have 2000 Watts of Light, 65 degree Farenheit Room Temp. And we want our Temp in grow rrom to be 75 degrees Farenheit.

3.2 x (W which is 2000) = 6400

In this case we divide by 10 since room temp. is 65 and we want an increase of 10 degrees to get to 75.

6400/10 = 640

So you would need 640 CFM of Exhaust Ventilation to keep the grow area at 75 degrees Farenheit if you have 2000 watts of light and a intake temp. of 65 degrees Farenheit.

Hope this helps.

DDub said:

Ok so if Temp in room is 70 right now the calculation I made in the post above is exactly what you need to exhaust this grow area, not the light.

The calcualtion I made above would keep your temp in the Homebox at about 75 Farenheit now and 80 Farenheit in summer, 80 is too warm. You need at least 250+ CFM just like I said at first.

I'll try to explain this Formula:

3.2 x W/T = CFM

( 3.2 is the only constant in this formula )

W= Watts of Light
T= Temp. increase from Room Temp.
CFM = Fan strength required

3.2 x (Watts) / (The Temp in degrees Farenheit Air will increase from Room Temp.) = Your required CFM's to keep Temp at Normal Room Temp plus (T)

So again in your case:

3.2 x 400watts= 1280
1280/5 ( 5 because you don't want Temp over 75 degrees Farenheit and you starting room Temp. is 70, so 70 + 5 ) You can substitute 5 with any number but this will be the increase from normal room temp.

So lets say we have 2000 Watts of Light, 65 degree Farenheit Room Temp. And we want our Temp in grow rrom to be 75 degrees Farenheit.

3.2 x (W which is 2000) = 6400

In this case we divide by 10 since room temp. is 65 and we want an increase of 10 degrees to get to 75.

6400/10 = 640

So you would need 640 CFM of Exhaust Ventilation to keep the grow area at 75 degrees Farenheit if you have 2000 watts of light and a intake temp. of 65 degrees Farenheit.

Hope this helps.

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Very informative! Can you tell me where the 3.2 comes from?

Great thanks, I would leave you rep but I don't know how to?

Where in the hell am I? said:

Very informative! Can you tell me where the 3.2 comes from?

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That is a very good question that I don't know the answer to.

**Also I must mention this does not refer to CFL lighting**

Only for MH/HPS lighting.

Also, is that constant? or just a few changes per hour will suffice on a timer?

DDub said:

That is a very good question that I don't know the answer to.

**Also I must mention this does not refer to CFL lighting**

Only for MH/HPS lighting.

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Ty! I knew that, but I appreciate ya lettin me know