Venting Using 2" PVC?

My first post here. Love this site. Tons of great info. I've spent the past couple of weeks reading and searching to pick up knowledge. I see a lot of posts here that could be answered with a simple search. I believing in doing homework before asking questions! That said, here is my case. I'm looking for a little help setting up my grow room. Here is what I've got.

Basement set up. Good climate control all year round. Ready access to electric and H20. Lockable and away from all utilities and systems that might need to be accessed. It's an A- on the rhizome scale. I'm planning a 3'6" x 3'6" x 7' enclosure lit by a 400w dual HPS/MH lighting. I'm going to construct a box and line it with mylar. Stealth is only an issue when it comes to odor and noise (hence the A-). I need to be able to entertain and have the in laws walking around in the living room directly upstairs with no odor and little noise. And naturally I'm concerned with heat from the light. So my issue is venting and scrubbing.

I've read and re-read the AWESOME Noob's Guide put together by rhizome and others. What a great place to start learning. Thanks. So I am familiar with the parameters of venting and scrubbing. I plan a vented hood that will be open to the grow room thereby venting both the light and the room.

My problem is that I only have one way to access an external vent - by tapping into my whole house vacuum exhaust which is 2" PVC piping. I was looking at a hood with a 6" exhaust but I'm now looking for a 4" exhaust hood (do they make a 2" exhaust hood? Would it work?) My thinking is that I will step down from 4" to 2" and out of the house. With a little negative air pressure I should not face any odor issues in the house. I'm not overly concerned with the back yard but don't want it to stink either. I figure that the setup will look like this:

Light hood > 4" exhaust tube > charcoal scrubber > inline fan > 4" exhaust tube >step down to 2" exhaust tube > 2" PVC > Y connector with vacuum vented outside.

Now I'm guessing that I will also need to find some kind of reverse air dam (not sure what it is called) that will go upstream of the Y connector such that the exhaust does not push back up the vacuum system for distribution throughout that house... That would definitely defeat the purpose.

Have any of the gurus here seen or heard of such a setup? Will I face issue stepping down from 4" to 2"? Does this seem feasible? If not I have to move out to a tent in the garage which will be very very limiting. rhizome would give my garage option a b- or perhaps c+...

Any advice appreciate!

Thinking about it a bit more I will also need a reverse air dam on both sides of the Y connector. I wouldn't want the vacuum discharging all over my grow room!

It's called a back draft damper. I can't seem to find a 4" to 2" duct reducer. Damn.

good luck finding anything smaller than 4" for ducting. I have never encountered 2" ventiation ducting of any sorts.

I wish they did make like 2" extraction fans and filters to match for miniature growing environments.

I'm not worried about the fan. It will be a 4" inline fan readily available. My concern is forcing it down to 2" where it meets the PVC. I have found a 4" to 2" reducer but it isn't actually a reducer in the true sense. It is a 4" to 2" PVC bushing and it doesn't reduce - it's an sharp angled reduction (90 degrees). This is going to be a custom job to be sure.

I've refined my rig config a bit:

charcoal scrubber > 4" exhaust duct > Light hood > 4" exhaust duct > inline fan > 4" exhaust duct > damper/draft control > step down to 2" exhaust PVC > Y connector with shared vacuum line > vents outside.

I'm guessing that I will need a speed control unit and that it will be a question of finding the optimal fan speed. Appreciate any help from the board before I go buying components. This is my only hope for external vent.

i don't think it will work going 4" to 2"... what about venting out the enclosure into the basement room?

may i suggest looking into LED lighting as it does not create any heat except about 3-4 degrees...then you might look at an ozonator for the odor....works really well...and quieter than a big fan with a carbon filter~then your 2" pvc would be taking some air out for circulating some air through your box...and some odor out to wherever your exhaust goes!:jointsmile:

Thanks for the feedback. Badly needed here!

bigtopsfinn, what make you think that it won't work? I respect your opinion and I am certainly willing to believe that it won't work but I'd like to confirm with facts or at least conjecture ;). Considering that it is possible to reduce from 6" to 4" why not for 4" to 2"? I realize that there are significant volume differences between 4" and 2" but enough to make it unworkable? What about my idea of using a speed control unit to adjust the air flow? Perhaps it says something that there are no reducers going from 4" to 2"?

stra8outtaWeed, I'm not sold on the LEDs. I've read very mixed reviews. I like the proven technology and results of the HID. I'll do some more reading. Concerning odor control, I have considered other options. My situation calls for 100% reliability. I have to be able to have very uptight work colleagues (including my boss and his boss) directly upstairs on a regular basis. I suppose I could do an internal filter and odor box but I'd MUCH prefer to vent everything out doors.

You raise a good point about fan noise. Can anyone comment on the noise level of inline fans?

Thanks guys. Keep the comments coming.

i am growing with 900w of LED that i did with 2000w of HPS and my weed is much stronger with the LED's...if you get good ones 300w of LED will blow your 400's away! So if you can find some good ones they are well worth it and they pay for themselves in energy savings and no bulbs to buy :thumbsup:

just something to look into with your situation....if your exhaust was bigger then i don't see any issues stopping you but heat could e a problem and only a 2" exhaust!:(

look at my bottom link...that is my LED grow and flower :jointsmile:

Sorry bigsby, it is more conjecture on my part, never tried a 2" exhaust. But I can say that I have a hard enough time maintaining temps on my 400w cab... small ducting, small fan and several bends in the duct make things more difficult.

If you do some calculations, the area of the duct (area of 6, 4 & 2 in. circles) and volume differences (cylinders) reducing from a 6" to 4" and 4" to 2" are pretty significant. You'll have to worry about the fan noise AND the whistling, pressurized exhaust air, and maintaining good temps might also be a problem... There's probably a good reason why 2" ducting isn't produced.

A lot depends on the temps in the basement too. In order to cool that 400w, you'll need a strong fan or cool intake temps (this would most likely require a heater for when the lights are off).

That's why I'm suggesting to keep all the exhaust in the basement if possible. Use a carbon filter in the growroom, and one in the basement room (or some other odor neutralizer). Then there are some instructions online for silencing inline fans, it think you'll be set.