Prep work's a drag, huh? Don't worry, it's all very worthwhile.

Shoulda mentioned last installment that you should snap or otherwise draw a line showing where your ceiling joists are. You can do it now,though.

So why do you need to know where your studs are?

I'm gonna actually refer you to another old fart . ( Go ahead, click the link)

You're going to hang an HID lamp from the ceiling. There are three ways that a fire can start in a growroom. One of them is to overload a circuit or powerstrip. Another is a flammable material too close to the lamp. The third is for your lamp to have fallen.

Go check out the first page of the ?? Plant Problems? forum. There's a new thread on there every single day where somebodies dropped their light onto their plants- and that's really a best case scenario. Worst case is that your light falls and ruptures the bulb, IGNITING A FIRE!! Somewhere in the middle is your light falling while you are working under it, causing painful burns. ( Painful, painful burns...)

Remember, the only constant in life is entropy- shit falls apart...

I don't regard an HID lamp as any more dangerous than a microwave oven. (That being said, I have rarely suspended my microwave over my head.)

The reason that you need to know where your studs are is that you are going to hang your HID lamp, from these joists.
Would you hang a microwave oven from string tied to a little wire hook in your ceiling drywall? If you would, would you take a bath underneath it?

Me, I'd use chain, hooks rated at least three times the load that I was going to hang on them, and I'd have those hooks very firmly mounted onto ceiling joists. But if I hung it, then yeah, I'd take a bath under it.

I'm sure that this sounds like hyperbole, and it sort of is- but the point is safety, so I don't feel bad about it.

By now, you should have a very specific plan of how your going to lay out your plants- if you don't, set up your containers, trays, what have you , and do a layout plan- figure out how you're going to water things, where things should go so that you can reach them easily- Frequently, it doesn't make sense to hang the light in the center of the room. It's a whole lot easier to re-arrange empty pots until you have something that works for you, than it is to move pots around to water. Make sure that there's room for you in there too, and that you'll be able to reach the pots with a full, heavy container of water- or if you're going to do hydro, that you'll be able to maneuver five gallon buckets of water in there, get nute samples easily, that kinda thing.

Anyway, do your layout, and get a look at where your plants are going to end up when they finish flowering. This is going to determine where you end up putting your light. Assuming that your walls are fairly level, you can take measurements on the floor and transcribe them to the ceiling- Just make marks on the floor and use a plumb bob. ( Borrow your grand-dads- it'll thrill him)

A quick tip- the great majority of the light from an HID lamp is emitted from the sides of the arc tube. I always try to align the arc tube so that it's parallel to the shorter walls of the room- this gives you the most efficient distribution pattern.

Personally, I like to have the light suspended from more than one joist, although I suppose that if you actually have a complete failure of a joist, the lamp will be the least of your problems.( I used to do swing stage work in an urban area- I'm really into redundant back-ups.) If I'm at ninety degrees to the joists, then a couple of hooks and we're done- if I'm parallel, I usually strap a plate across two joists and sink the hook in that. This also adds a lot of flexibility in placing the light, as I'm not stuck with the joist layout- if I want to be six inches further over, I have the option.

Hooks and chains are load rated. Always at least triple the load rating- ie a 20# reflector requires hooks and chains load rated at at least sixty #s. It's the cheapest insurance you'll ever buy, and the most likely to pay off. ( Speaking of which, if your homeowners underwriter ever finds out about you're doing this, they will never pay any claims for any damage- Are you going to walk into a courtroom and sue your insurer because they wouldn't pay for fire damage caused by your garden? Me neither.)

It's a really good idea to pick one hook on any given chain that you're going to use for adjustments, and crimp the others or otherwise ensure that they cannot possibly dislodge. Play out scenarios like:

You have walked into the room and tripped, falling directly onto the reflector.
Will your body weight pushing it to one side knock it off a hook?

You have been crouched over under the lamp, and misjudged it's location. When you straighten up, the back of your head touched the bulb- causing instant, searing (literally) pain. You thrash about.
Can you knock any of the hooks out by taking weight off of them or shaking them back and forth?

These things happen, and suck.

But they suck even more if they end up dropping your lamp onto your plants, onto your head, or into some water.

Ok, are you happy with where your reflectors hung, how it's hung, what it's hung with? Great- take it down. We need to strap more stuff on the ceiling- we did the light first because it's big, and position sensitive.

I usually do the carbon filter on the ceiling as well, hung from hook and chain. It's not as critical to have the filter perfectly positioned- Nice to have it nearish the light, as that's where airs often hottest, and center of spaceish- but pretty much anywhere reasonable on the ceiling's gonna do. As the filter will neither burn me or start a fire, I usually just hang it off one of the joists- sink two hooks, put chain on them, hold the filter up, wrap chains around filter and back onto same hook. Good idea to check the fit with the reflector back in place- also to make sure that it's really as easy to move the reflector around as you expected. Try to point the flange end of the filter toward the exhaust flange you installed earlier, or at least not away from it. The fan goes anywhere that's good between the two- again, heavy, joist. The fan will seem quieter from outside the room, where it matters, if there's flex ducting between it and the exhaust flange, and if you suspend it from a piece of chain or bungee, so it's vibration is not transmitted to the joist.

Now lay out your ducting, cut it to a good fit (Not so short that it wants to pull off the flanges, not so long that it's all over the place) For this, I use drywall hooks and cable ties- it doesn't weigh anything.

Ok, so we have your ventilation in place, with the cord from the fan just hanging down. Go ahead and hang the reflector back up, (no bulb just yet, and with the lamp cord unplugged from the ballast, if you can,) stand back, and admire your work. It's starting to look like a growroom in there.:thumbsup:

Let's break again here, and pick up with cable routing, environmental controllers, timers, and keeping the ballast off of the floor and therefore out of the water.