Venting this underground room.

Nobody? ........ Chirp.......... Chirp......

It's sort of absurd to expect to ventilate 10'x12'x10' (1200cu. ft.) and 6'x10'x10' (720 cu. ft) with 4"...anything. A full 14" (16" on center) stud space (54 sq. in. - roughly equivalent to one 8" or two 6" ducts) might work to take air out of the space but where does it go? Where is fresh air going to come from?

I certainly understand the attraction of growing below the frost line (particularly in AK) but if this space is totally buried (like a bomb shelter or something) then humidity will most likely be a problem (along with the mold/fungus that plagues dank/humid spaces). But then if it was actually a bomb shelter then it should already have ventilation/filtration better than you'd need. I guess you could (partly) get around the porosity of concrete by framing in a "room within a room". But if the walls in your diagram are already there... Of what materials are they made? Can you frame out "room within a room" walls? They'd help to keep temperatures more stable, anyway, but I still think you'll need gallons and gallons of dehumidification (good thing there are drains all over the place, eh?)

The more I think about your space, the more I think you may be better off sealing it up; going the "climate control and CO2" route. You could use a single stud space on either end (in and out) for the lamp heat in the flowering room (use a "T" or "Y" fitting to go from 6" to 8" and then into the wall on the way out; do the reverse on the way in). But the exterior walls are concrete... Dammit.

The real problem would be controlling climate in each grow space (as cannabis generally prefers slightly different conditions during veg and flowering). Either you could control the climate in the entire space using a heat pump and humidifier/dehumidifier (then use passive intakes and temperature-controlled fans in each grow room to spit "bad" air out to the big room) or you could put a heat pump (and other climate control machines) in each room. I guess you could get a two-zone heat pump and use each "head" for a room. If your condensers were in the big room, though, it would become a fungus factory in short order without adequate dehumidification...

Good Gawd, what a nightmare. I hope you're a secret millionaire so you can afford all the crap you'll need to make this work... But not having seen your space, and having no idea what the temp/RH are like in there without plants, I can't do much apart from spitballing ideas at you. In the end, you're the one that has to make this space work. I wish you much success.

not a nightmare at all. easy to fix. you say you want a sealed room but you want to air cool the lights.then do a real sealed room and forget air cooling, you can still use the reflectors or get parabolics, and just get a 18000 btu minisplit ac. my 12000btu easily handles 3k non aircooled,ballasts,dehumidifier, and feeds the veg room both equaling 110sf. no leaks to worry about, no odor problems. plus your plants will love the bulbs not being behind glass.

Ok, let me simplify........

The drawing I provided IS what I am going to build (start in a couple weeks), so it's NOT a pipe dream; just need to research it, and doing so.

So, I gave you the footprint, help me out. Ok, 4" intake/out take wont work; fine! Tell me what will. This project is in the 25k range, the price is not the problem. Setting it up to be completely auto, is the problem. I need to know, that's why I asked; go figure! The building will be underground, 4" slab, 6" concrete walls poured in "quadralock" blocks (2 1/2" styrofoam both sides).

Not hard to figure out, air comes in from 'outside', and then vents 'outside'.

I stated I could use "any kind" of venting; piping or tin vent style. Its not built 'YET' hence the question(s).

You have the dimensions, you have the understanding of what I'm trying to do; so why a long winded post of.............. ?

if you still insist on the venting, although a sealed room is beter, the box vent will be 3-4x as much volume as 4"pipe.

i would run a 10" or 12" in and out.

my only question is if you plan on running 3600w in your flower room...exactly how many CFL's are you running in your veg room? you might want to look into T5's or MH. might be a lot more efficient.

i also agree with above. get rid of the intake/exhausts alltogether and run a truely sealed room with Co2. if you completely seal the room then you may just want 2 4" exhausts that run at night to exchange the air in the room. i've seen a lot of growers switching to this model with good results. you would just need to make sure that your exhausts are filtered for odor.

a sealed room is a sealed room. there is no need to exchange air. you provide the enviroment. plants need light,food, water and co2 not fresh air they provide that.