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Thread: Replacing standard flex duct with insulated R8 flex ducting - Condensation issue

  1. #1

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    Default Replacing standard flex duct with insulated R8 flex ducting - Condensation issue

    Heyo!

    We'll I'm about 45 days into my new grow, this is my second grow. 1st grow started in March of '20, although it was cold, it was not as cold and condensation did not appear as much of a problem as it now. My grow tents are in my insulated attic.

    I' ve added a 2nd 3x5 tent along with the original 4x4 tent. I have Y's for both the 6" intake and 8" exhaust. This allows me to use the same two roof vents, one for dedicated fresh air and one dedicated for exhaust and are shared between the two tents. The intake & exhaust are NOT mixed, they are both separate and dedicated to their purpose.

    I've also made some modifications to the tent by adding insulated foam board, to the 3 primary sides and roof and adds an R6 value. I cut holes in the foam board for the 6" intake and 8" exhaust. For the front door of the tent, I zipped up two sleeping bags as a drape for the front entrance for both tents. It's a pretty nice setup, I'll be certain to add pictures once it's complete.

    On to my problem. Last week I went up to water, and noticed water on the floor, outside of the 4x4 tent. That tent sits on a 6x6 platform over the insulated floor of the attic.
    Initially, I noticed it was coming from the outside flex duct of the 6" intake, closest to the tent. I dismantled the flex duct and noticed it had a wet interior throughout. Then I checked the 8" exhaust, and felt weight of actual water inside the flex duct, which thankfully, I was able to drain without further issue.

    The issue is easy to understand, hot air escaping into non-insulted ductwork that is just above freezing, gets you condensation. I didn't have this problem on my first run, because the temps were more mild and 3 internal fans for air movement.

    I purchased 25' of both 6" and 8" R8 insulated flex duct and also picked up 3 - 6" & 3 - 8" spring loaded dampers. My plan is to add the dampers at the initial exits of tent and roof (for both tents). The galvanized Y's are closest to the roof, and the dampers are before the Y at the roof, and before the inline fans at the exits of the tents. I'll include a drawing of this as well.

    Once completed, I hope to achieve airflow that doesn't create condensation build up in the ductwork. When I inspected the original flex duct, there was a lot of dust inside and in the original inline 6" fan had mold. I cleaned the inline fan with bleach, and thankfully wasn't using it, as the temps were just to cold to add cold fresh air. But so glad I'm doing this as I've discovered a lot of issues as a result.

    I'm currently using one tent at the moment, not taking in fresh air from the outside, only from inside my home using a 6" inline fan with insulated ductwork. Thankfully, I had the knowledge to buy insulated duct for this single run, because it pulls both AC as well as heat - no condensation issues - but I will be inspecting to confirm this.

    It's a battle, but I'm committed to making it work. Please let me know if you have additional ideas for me to implement.

    Thanks,

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  3. #2

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    An interesting read... I don't get these issues & wonder if some of it is due to low humidity in my groom... along with my 24/0 lighting?
    It's Not What You Know, It's What You Can Prove

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  5. #3

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    It's definitely dry humidity here in the North Central US. The attic is about the same as outside, the floor of the attic is all blown in insulation, about 16". So any air flowing through the flex ducting is warmer than the attic air tepm and causing the condensation. I haven't used the inline fans consistently this round as it lowered the internal tent temps too much.

    Once I have all the insulated duct in place, I will see how it works. I want fresh air in and exhaust the stale air. Thinking of doing 6 minutes exhaust and within the 6 minutes of exhaust, run the fresh air intake on the first 3 minutes. Every three and a half hours.

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    Wanted to upload these photos a while back.

    This looks very industrial now. This upgrade still does not fully address the condensation issue for my attic set up.
    Overall, the inline fans for each tent's intake, are joined together using a Y Connector. The same set up is repeated for both tent's exhaust feature. I use a timer with both setups, running the intake the first 3 minutes of each our and then the exhaust runs the next three minutes. If I don't do this, I see condensation form on the outside of the inline fan motor casing. Each night I'm visiting, I run the fan for 15 min to move out any condensation existing in the insulated vent. My obvious concern is mold, so I'm trying to be vigil with this. Click image for larger version. 

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    If you have any advice, do tell.

    Thanks!

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  9. #5

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    imo your attic could do with a bespoke outlet vent. Angled so that any condensate runs downwards and onto the roof, not into the fan. Would be awkward to make or spendy to have fabricated but only needs to be done once.

    If the fan is slightly off horizontal, say 15 degrees with the outlet end the lowest, the plate that the solid ducting is joined to needs to have an elliptical hole cut in it. Cut the angle in the pipe first and use that to mark out the ellipse on the plate. Welded together if steel or strong glue if plastic. Fan hung up high and taped directly to the angled outlet vent. Then, if there is condensation inside the ducting, it does minimal harm as it runs down.

    I like to figure out how I would use other peoples grow space and as you asked for any ideas...

    ... I'm a minimalist with an aversion to ducting. I'm probably too Spartan for most but if I can do without using something and not risk running dry, why would I make an extra effort? I'm self sufficient either way.

    For years, I've been using open cabs in my cellar. Imagine a 4'x4' tent frame, just the metal poles. Hang the light from the top and wrap Orca around the outside. Held by spring clips. So that the top of the Orca only just covers the highest that the reflector is likely to be. That gives a 16 sft passive inlet and a 16 sft passive outlet. Warm air up and out, cool air in from the bottom. Chimney effect. For the plants to overheat, the entire room has to overheat. That's not going to happen in my cellar. I didn't have any tent poles so I made the frames with 2"x2" timber and used 4'x4' white faced mdf as the 'walls'.

    I once ran 3 open cabs as a staggered harvest. A harvest every 5 weeks. Whichever cab was currently in veg had a 15w pygmy incandescent bulb on a dimmer laying on the scrog screen. Enough light to stop them flowering, not enough light escaping the cab to bugger up the flowering plants. Was a very dim glow outside the vegging cab. A problem with staggered harvest is that it takes ages to start and/or stop. Before I knew it, I had 2 years supply of weed jarred up and I was caning it back then. Took me 15 weeks to wind up the grow.

    My last cellar grows were 6'x6' scrogs using three 6'x2' trolleys on castors. As I was only doing one, maybe two grows a year, I removed the (worn out) filter from the 6" outlet fan and didn't replace it. My main cellar room is also my workshop and needs the fan running all the time or it gets musty down there. I wasn't going to wear out a filter when I didn't have a grow going. So I had an 8" fan and filter taped together as an air scrubber close to the grow to control odour. What odour did come out of the airbrick dissipated a few feet from it. If someone takes the trouble to kneel down and sniff my airbricks, I'm already in trouble. Can't see anyone climbing your roof to sniff the outlet vent.

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  11. #6

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    e2a: The angle of the roof needs to be considered. If the roof is say 45 degrees and the fan is to be 15 degrees off horizontal, then the angle to cut the pipe is 60 degrees.

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