where to vent exhaust?

this is my first serious attempt at growing indoors. i'm getting my 10x10' room ready for flowering. vegging under HO T5s right now in the closet of that room. planning to run (2) 600watt HPS aircooled tubes similar to what this guy did: http://www.youtube.com/watch?v=RnQ9BzVaJ80

for air intake into the room, i plan to just use the existing ducting in the house. this particular room has a 5" insulated duct going to it. i was going to add a booster fan and just let the cool air spill into the room from the vent on the ceiling. i figured that even if the central a/c is off, the fan would still be pulling some (presumably) cooler air into the room. would it be better to upgrade the ducting to 6" or even 8"?

i built a DIY scrubber using instructions found here: http://forums.mycotopia.net/cannabis/8038-diy-carbon-scrubber.html. mine is 24" long and activated carbon trapped between 8" and 6" diameter screen. surface area works out to 4.2 sqft. i used aluminum screen instead of pantyhose and used bamboo/cotton batting on the outside since it's a little less flammable than polyester.

i'm planning to hang the scrubber close to the ceiling, running 6" duct to the bottom of the first tube, coming out the top and into the bottom of the second tube, then out the top again, where it's being pulled by an el cheapo suncourt 6" duct fan rated at 160cfm (free air, unboosted). that should be sufficient to cool (2) 600watt HPS, right?

i was going to run the exhaust into one of several places (with another booster fan pulling from the far end):

1. the dryer vent is very close to this room. i could just pump it out the dryer vent, but i hear police helicopters flying over my neighborhood once or twice a week and am a little paranoid about a strong infrared heat signature constantly being emitted from that vent. yes, technically cops need to have a court order, but...

2. back to the return air duct. issue here is stale air. when the a/c is running, it will mix the air with fresh air coming in from the main return air intake, but when it's not running, it's almost a closed system. it's just going to recirculate the same hot, moist air.

3. out a vent in the laundry room, which is right next to the central a/c thermostat. my rationale is that as the warm air fills the laundry room and spills out the open door, the warm air will kick on the a/c.

4. into the master bathroom, which is always cold due to the fact that it is north facing and the bedroom and bathroom flooring is tile (seems to have a small but noticeable geothermal cooling effect). i'm leaning toward this option since the exhaust fan noise will be isolated to the master bath/bedroom and since no hot air is actually vented outside the house.

is hooking into my central a/c not a good idea? my gut tells me i need more air coming into the room. how/where should i vent? thanks in advance for any advice.

vent straight outside thru a door or window or thru the roof. Hooking into a central ac isnt bad unless you want the place NOT to smell like cannabis

If smells not an issue (i.e. you have it under control) I'd just vent into a heat duct or ac duct. That way your heat signature blends in with your home's ambient heat. In the summer time your ac should in theory cool your heated air too. Obviously this is pending that you have central ac and heating. Other wise I'd just vent in a crawl space bellow your home. Just about every video I've seen on flair detection prevention has said to try not to vent heat outside. Try to get your heat signature to match your home's radiant temps. You should try not to vent in an attic since hot air tend to move up. That might be suspect.

2 600w lights shouldn't put too much a dent into your total home's radiant heat signature. Something like 4-5 1000w would be suspect. In the grand scheme of things 2 600wers are small potatoes in terms of light setups...Hell 2 1000wers are too. Obviously a larger light setup shouldn't be vented in your home. 4-5 lights put up a lot of heat.

2 lights in either the 600-1000w range shouldn't raise your home's temps much more than a degree or so. It's also not suspect for heat vents and interior pipping to be 10-30 degrees above room temp. I'd go this route if I were you.

thanks, ronjohn.

10 pounds of activated carbon should do the trick as far as odor, i'm guessing, especially for a small grow.

starting with (2) 600s but want to built out my room to be able to scale up to more light/heat down the road. i doubt i'll ever go beyond 3000watts total.

some have suggested that as far as cfms, you want to be able to change the air every minute. that would mean my 10x10x10' room would need a 1000cfm of ventilation? while it might seem overkill for (2) 600s, i want to be able to scale up to 3000watts. thinking of getting an inline centrifugal fan in the 1000cfm range that can be dialed down using a dimmer switch. any suggestions as far as (quiet) fans?

you just about answered your own question. if your gonna get a dimmer/ fan controller switch, you would just want to get a large enough fan to compensate the dimmer. for example, if your room needs a 1000 cfm and you plan on running on 1/2 power to control sound, you want to get a far bigger fan to make up for the cfm loss. 1500 maybe 2000 cfm. but for 2 600's, 1000cfm fan on a dimmer should do it. you may also wanna look into a muffler. their a little pricey but i hear they are bad ass.

To find how to cool your room look up a CFM calculator.

If you're air cooling your hoods (i.e. cool tubes, or airtight reflector) then you need roughly 100-200 CFMs per hood. 1000w hoods need are 160-200 cfms per hood. You most likely need something in the 200 cfm range. You don't want to get too large of a fan since it's a waste of power and it won't cool your hoods properly (too large of a fan will actually make them run hotter).

man, just looked into 1000cfm: 12" intake! i think that's overkill. 200cfm x 2 sounds about right. looking to pick up active air 6" 400cfm inline fan.

Every room with a A/C/heating duct will also have a cold air return vent. Cut yourself a piece of 3/8 plywood to replace the vent cover. Cut a 6" or 8" hole in the new cover and attach an adapter to receive your exhaust air vent tube from your filter and/or cool tubes. It is a good idea to install vent back flow valves in case of a power outage. (If the the exhaust fan stops the flow valves will close limiting the unfiltered odors from entering the A/C heat or cold air return vents.) Leave the furnace fan on 24/7 and it will distribute the heat EVENLY throughout the building. 3 - 600W cool tubes can seriously augment if not supply all your heating requirements during the winter months. Using a quality carbon filter, you can't smell a thing. Another benefit is that you are not exhausting hot air outside which generates steam and possibly unwanted attention to your hydroponic garden. In the summer months you may want to locate a sewer pipe. Each pipe has a service port sometimes near the base of the wall. To locate these drainage pipes just run your shower, sink or what have you and listen for the sound. You will need an adapter from your 6" or 8" exhaust vent down to the 4" drainage pipe. In case of a power outage, a back flow valve is imperative. In the winter you seal off the pipe preventing all odor. A 4" sewer pipe will restrict the exhaust flow and if you ever have to clean a trap you will want to shut off your fan otherwise you will discover forced air coming from the open pipe. Water in your traps prevents any air flow out of drains.. I have heard of some people forcing unfiltered air into the sewer drain however I don't recommend it. In the case of a condo or town home I would be particularly cautious that you are not sharing plumbing with your neighbors.