Let's Settle This! 250w vs 400w: A common question with conflicting answers.

Greenscience

Greenscience

Member
Hey Everyone!

First post on this forum and I'd like to thank everyone in advance for taking the time to help a grower new to indoor gardening. Hopefully this thread can also help many others with similar dilemmas.

My growbox has been built with 2'D x 3'W x 4'H dimensions as this fit my space and security limitations. The problem is that I'm a little concerned about diving headfirst into the the lighting and ventilation. Money is not so much an issue as is security but I would still like to avoid making expensive mistakes.

I tend to see a lot of conflicting opinions regarding the light limitations of this sized box. My box will be a dual lighting ScroG system with Metal Halide for vegetation and HPS for flowering. My instinct is telling me that a 400w would be best but I'm concerned that even with an air-cooled hood, temps would become too high. On the opposite end, I'm not afraid of heat issues with a 250w as much as cutting myself short on yield.

Secondly, a concern I have is the type and amount of ventilation to use. I've considered isolating the lighting system ventilation entirely which would require secondary ventilation for the replenishment of CO2 in box environment. I have no plans of CO2 enrichment for my first indoor grow so that is not a consideration. I've read some interesting artilces on ventilation and I have to admit that, though they are well written, they don't make much sense (to me). Especially with regards to overventilation causing plant stress. My intake plans are passive and the exhaust will be pulling through a 4" Organic Charcoal Filter.

Here is where I ask for the help of you seasoned veterans! Please advise on my lighting and ventilation system ideas. Advice from those with experience in similar systems or those with years of experience is especially welcome.
 
YungMoolaBaby

YungMoolaBaby

Well-Known Member
Well if you are splitting the room into two I would go with the 250 w because heat won't nearly be as big as an issue if you were to squeeze a 400w in there.
Not to mention if you have a veg area right above your flowering area, you shouldn't worry about yield just because you can perpetually harvest plants. You can have a clone(s) in waiting while your other plant(s) are doing their scrog thing, but there isn't going to be a whole lot of room.
 
jawbrodt

jawbrodt

Well-Known Member
Are you splitting that area in two, or is that the size of each area?

If each area is that big, I'd go with a 400 MH for veg, and a 250 HPS for bloom. They both output the same amount of lumens, so that would keep it balanced. It will also keep the 'lumens per square foot' up around 5,000, which is getting into the 'sweet zone'. :cool: If you went with a 250 MH, that would push the lumens per sq foot down close to 3000, which is near the minimum that you would ever want to go. I know heat is a big issue for you, so I will just say this....the 400 watt MH will put out the same heat as the 250 HPS, so I'd go with the 400 if you want shorter bushier plants. If you went with the 250, the output will be close to that level where they will start stretching. Since you said money isn't a huge issue, I'd go with that setup, using ventilated hoods, preferably a rectangular model since your grow area is rectangular. It'll give you more even coverage. You might not be able to keep the temps down in the 75* range, but they will be fine up to the 85* range, and even a little higher. I had hot days this summer, up a little over 95*, and I have no issues, and still got a nice yield. I just had to water everyday, and they grew great.

If you're dividing that area in half, the 250's will be plenty. The 175's will probably even cover that are well. I'm not sure of their output, so you'd have to look it up and do the math. I like to keep mine at 3,500+ output at the weaker 'outer' areas of coverage, and most will agree that you wouldn't want to go much lower than that. :)
 
Greenscience

Greenscience

Member
jawbrodt said:
Are you splitting that area in two, or is that the size of each area?

If each area is that big, I'd go with a 400 MH for veg, and a 250 HPS for bloom. They both output the same amount of lumens, so that would keep it balanced. It will also keep the 'lumens per square foot' up around 5,000, which is getting into the 'sweet zone'. :cool: If you went with a 250 MH, that would push the lumens per sq foot down close to 3000, which is near the minimum that you would ever want to go. I know heat is a big issue for you, so I will just say this....the 400 watt MH will put out the same heat as the 250 HPS, so I'd go with the 400 if you want shorter bushier plants. If you went with the 250, the output will be close to that level where they will start stretching. Since you said money isn't a huge issue, I'd go with that setup, using ventilated hoods, preferably a rectangular model since your grow area is rectangular. It'll give you more even coverage. You might not be able to keep the temps down in the 75* range, but they will be fine up to the 85* range, and even a little higher. I had hot days this summer, up a little over 95*, and I have no issues, and still got a nice yield. I just had to water everyday, and they grew great.

If you're dividing that area in half, the 250's will be plenty. The 175's will probably even cover that are well. I'm not sure of their output, so you'd have to look it up and do the math. I like to keep mine at 3,500+ output at the weaker 'outer' areas of coverage, and most will agree that you wouldn't want to go much lower than that. :)
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Thanks for the awesome reply. 2 things to point out that I didn't mention originally. This is a DIY bubbleponic (basically a DWC, with continuous pump feeding). Also, for my first indoor grow I didn't set this up to be a perpetual harvest. As this is only for personal use, and will only hold 2 plants being a Scrog, I wanted to get a feel for what I was getting into and what the yield would be, as well as finding the kinks with my system, etc. That being said vegetation and flowering are taking place in this entire area and I'm switching bulbs at the change in photoperiods. The only thing that would be seperated is seedling growth.
 
M

mrmadcow

Well-Known Member
go for the 400! w/ an air cooled hood or a cooltube,heat wont be as much of an issue as you seem to think.consider using a hood w/ a seperate intake so you wont have to run it through the filter,doing this means a PC fan could be used for its airflow.
if still in doubt,a 250 will work & you could add a few CFL to spread the light to the far corners
 
Greenscience

Greenscience

Member
mrmadcow said:
go for the 400! w/ an air cooled hood or a cooltube,heat wont be as much of an issue as you seem to think.consider using a hood w/ a seperate intake so you wont have to run it through the filter,doing this means a PC fan could be used for its airflow.
if still in doubt,a 250 will work & you could add a few CFL to spread the light to the far corners
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Thanks mrmadcow! It's good to get some reassurance on my original idea. Although 250w would be the safe bet for this size, I think I'm just going to live'n'learn. It was always the plan to have the light air-cooled separately. (not through the filter) Does air-cooling a rectangle hood require fans on both sides?Intake and exhaust? Also, what is the threshold on benefit from air-cooling a light. At a certain cfm, I imagine you could no longer gain benefit.
 
stumps

stumps

Well-Known Member
you can se a cooltube so you have almost o heat from the light. even with my fans lacking I can keep my 400 off the tops about 4-6".I don't I like about a foot.
 
M

mrmadcow

Well-Known Member
Greenscience said:
.... Does air-cooling a rectangle hood require fans on both sides?Intake and exhaust? Also, what is the threshold on benefit from air-cooling a light. At a certain cfm, I imagine you could no longer gain benefit.
Click to expand...
if you have any concern about smell escaping,I would put the fan on the intake to blow air into the hood,that way it will have positive pressure and force air out any leaks into your grow chamber where your filter will deal w/ it.if you put the fan at the end to suck air,it will suck air (and smell)in from your grow and dump it out the unfiltered exhaust.
Im guessing your right about the cfm.Ive only done 1 cooltube for a small closet.a 250 watt hps w/ a hurricane lamp globe and a PC fan. after running for several hrs,the globe was warm but not too hot to hold.it worked so well I had to come up w/ a heat source for the closet as it was in a basement & temps were below 65.
 
Greenscience

Greenscience

Member
mrmadcow said:
if you have any concern about smell escaping,I would put the fan on the intake to blow air into the hood,that way it will have positive pressure and force air out any leaks into your grow chamber where your filter will deal w/ it.if you put the fan at the end to suck air,it will suck air (and smell)in from your grow and dump it out the unfiltered exhaust.
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Thats an interesting point. I didn't consider grow air being pulled into the light ventilation through leaks by sucking air through the system. Pushing the air through just doesn't seem like it would work though. This will require some research to see what others have done.:dunce:
 
ataxia

ataxia

Well-Known Member
great thread ..i'm keeping my eye on this ..I've been asking this quesiton all over the place for a 2x4x5 tent where heat is an issue. don't know what kind of hid to go with for flowering but vegging with cfl. i'd like some t5 advice for flowering and vegging......sorry bro ..i'll post a thread of my own..peace
 
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