Question about venting a 400w hps

Okay, quick intro…Haven’t grown a plant in 30 years, and certainly nothing on par with today’s strains or systems. Long story short, I used to grow whatever decent seeds I could get ahold of using a basic fluorescent grow light and miracle grow. Stumbled across the ILGM site whilst carousing the internet a little bit ago and decided to try my hand at one of these advanced strains.

I plan on trying some blueberry autos, and for my grow area, I’ll be using an old basement shower that’s 3x3x6 1/2. After driving myself near batshit crazy looking at all the different lighting options, I’ve settled on a 400w HPS.

My question is about how much venting I’ll need. I was considering the possibility of hanging a carbon filter in the shower, run 4" vent tube from it, through a cooled reflector, and connecting it to the cold air intake of my HVAC system. I’m just not sure, with either the furnace or the ac only coming on sporadically as needed, will that be enough for the amount of heat that a 400w hps generates?

Is it worth trying that or do I need to just scrape up some more money for a proper exhaust fan?

Many of us improvise the only way to tell is to try it an if the heats to high you can handle that to with minor adjustments

1 Like

all carbon filters are rated for a minimum cfm in order to be effective too little they will not draw air too much they won’t filter smell. When you buy a filter they usually recommend a fan size for it but as far as using your HVAC won’t be enough to keep smell down or to cool lamp :slight_smile: you can however use your exhaust from filter to cool your light on it’s way out and given enough of a draw it will pull fresh air in. This makes the 1 fan do 3 jobs and I use this trick with decent effectiveness mind you I overkill on my air exchange rates but it does work.


Thanks to both of you. I guess I’m off to do some more shopping.
Anybody have any good recommendations? I would like to go 4" I think.

My advice to you would be get anything out of your grow room and get temp- rh- right. I say this because you’re first mistake is choosing auto flower, and blueberry is super sensitive in auto. Here’s a pic of my closet. My mistake was trying Auto’s. Very unstable, like all 16 cracked within15 hrs, then half stopped growing, the four into rock wool, four into a soil largest pot I could fit, even tried a pvc 3 ft 4in tube as pot. YOU CAN’T TRANSPLANT. Don’t even try I didn’t even expose any root, I cut pot in half and set into larger one. My blueberry auto stressed to death. All rock wool sprouts took forever, not even growing them, any young stress stunts them to like 50 percent potential. Sprout to final pot and don’t touch. Not good for your skill level. Be realistic, grow regular fem seeds or clones from trusted source. You can’t kill them, you can do wonders with a three plants in a closet with a scrog . Top second set, train branches down, bend head to pot level, leave her couple days to adjust and keep training new growth. Put up screen and lollipop underneath. This will take 45 days to do small and bushy, then flower them to finish thru screen. You can’t loose with a stable strain grown indoor. Merry Christmas from the Barrieault family.

oh yes, I’m currently running 100,000 lumens at 90degree, at 78$ a month… Lol life is good. I love growing marijuana


Keithkush75, thank you for the valuable feedback. I may have been a bit anxious deciding to go with Autos. I think I will heed your advice…get my grow room right and try out some bag seeds or more stable strains first.

When I setup a grow room I build it dry (no plants) run it for several days to try and dial in my temps and set airflow levels to remain stable 68f dark 76f lights on good neg air pressure so stink won’t go unfiltered. After I have it dialled in so to speak I add my pots no plants just moist soil to see how humidity will be at it’s moistest point right after water :wink: this lets me know if humidifier is likely to be needed or not. Basically what I am saying is choose your plants after you know your room you are mother nature and need your shit in order before plants are there. This lets you concentrate on nothing but your plants needs and wants when you start it reduces stress to both you and your plants by being able to chew off one problem at a time with no rush to have fixed instantly :slight_smile:

1 Like

As for fem vs auto you have support here which will walk you right through either grow start to finish so it’s a matter of preference more than anything Auto’s are awesome for a first grow you don’t top them train them or transplant so lets you focus on the core of every successful grow proper feeding ph and environment. Reg fem let you train top transplant clone and veg longer so many skills to learn all at once so realy is personal choice thing

1 Like

I agree that autos might not be the best plant to start with for a beginner as they are much less forgiving of mistakes.

Apparently they can be topped, at least some strains, if done with care.

Also, it turns out they are not necessarily faster, or a shorter time from seed to harvest, than regulars. Especially as growing from clone with a regular photo-period plant, you can get a harvest in easily as short of a time period.

However, if you have an indoor environment, where you can not intentionally shorten the light period to induce flowering, then an auto can be useful. Or if you need to grow outdoors in the early spring/summer and you want a plant that will finish in a few short months instead of growing all year until the natural fall/winter light cycle drops to short enough to induce flowering, again, autos can be very useful.

Happy growing,


1 Like

You are a very smart man Donaldj. It couldn’t have been said better. I on the other hand should have forgotten most of what I know about creating monster plants from start. Autos were 50percent successful for me, you might be interested in seeing how this sugar baby auto fem from Kiwi seeds, I potted her directly into a 30 in pvc 4" pipe with soil and perlite approx 4"on bottom vented with lower airflow. I am hoping for a super tall large single cola, if it’s successful I can place them on a raised floor with fans under aiming up, and fit like 50 in a closet, a run could get me around 50 ozs of cola in 70 days. I messed up my first six that were ready because I was not treating them any different from regs .seeds . I thought I was that good, lol. I placed the other 6 directly in soil no messin with them. I just purchased a 600 watt cool tube digital ballast Mh/hps bulbs, timer, hangers , inline, clamps and pipes on Amazon, total was only 179$ +24+6+4= about 215$. Two day free delivery. Tell your boy they have all watt combos complete. Cheap. Good quality. Plus I’m running a sun blaze48 on 4 and 4 cool warm. And two 150 cfls. Total about 90,000 lumens 3 to 1 cool to warm for veg, then I’ll reverse it, then finish full warm. Is that about as optimum as I can give them. Th is 30%, temp 78. . Merry Christmas

just added a/c. Dropped temp from new light to 78

1 Like