Inline fan and length of ducting run

[Hawk]

How much flow is lost through having long ducting runs? Somewhere on the order of 30-40 feet from cab exit to final exhaust exit. This would be for a 6" inline in the 450cfm range. I'm planning on using a pair of such fans which I believe would normally be overkill for my needs (250w HID + some flouros in a veg chamber + ballast heat, in a ~40 cubic feet of cab). Cab temps can't be more than 5 degrees above ambient (2 or three would be better). But I want to be as sure as I can be that a long duct run isn't going to cut my flow down to 1/4 (or whatever) from what it could/should be.

I'd use rigid ducting as much as I could. The majority of that distance could likely be a straight shot.

Pulling is better than pushing, right? It's be better to have the fans located at the end of the run? I hope so because that would be a lot easier for me. My attic is a nightmare to work in.

thanks

 

[Hawk]

No one is running really long ducting?

 

[Albert Hofmann]

that is a really long run...I would say 2 450's would definately get the job done for a 40cf space. Yes, put the fans at the end of the runs and MAKE DAMN SURE THE DUCTING IS SEALED...otherwise the setup will work like shit


have fun,
albert

 

[Guest]

I think that's right. The longer the run the greater the chance for air leaks. Gotta be real carefull to seal everything up.

 

[Microwido]

For air filters, pulling is better than pushing. For ducting, I am not sure. I have my air filter in the room pulling through the air filter, and then pushing it through about 10 ft. of ducting.

For that long of a run, I would want the fan in the room, not at the end of the run. You need negative air pressure in the room, and the farther the fan is away, the less likely that will hold true.

 

[Albert Hofmann]

what I posted isn't up for debate...it is simply correct. Filters in the room fans as close to the end of the runs as possible, seal everything, done

albert

 

[Hawk]

So my filters should be at the intake side? I was hoping to put them on the exhaust side up in the attic with the fans (the end of the run). I'll have to really think about how I'd arrange everything in order to get the filters in the box. Plus, I'll need/want to muffle the exhaust outlets somewhat and I was thinking carbon filters might accomplish that to the degree I require.

Yes, I will be sure to seal everything well. I wonder if 6" pvc pipe would work up in the attic? I've never really worked with metal ducting but I have worked with pvc pipe some. Seems like it would be easy (relatively) to install and easy to seal the joints. Plus, I might be able to heat and bend it some as required for mild turns. Dunno, just thinking through the options.

 

[Harry Gypsna]

your filter can go on the other end being blown out of.... All the filters ive used have been suitable for use either way-either sucking or blowing....

 

[darthvapor]

can fan max are good for long runs or runs that have lots of bends. The airflow is much more streamlined so its like a jet coming out the fan and not so much air loss on the sides. helps to get the air moving better on your long runs.

 

[2buds]

So if leaks are prone to reducing suction then why not blow it out instead of sucking it out so even if you get a leak it has no ill effect on your volume of air being drawn out of your grow? No trip to the attic to repair a leak. I think I broke the law here but that is a flip side to the coin,NO? Also, with that much duct BEHIND a fan, your gonna lose a lot of air noise,NO? Increasing teh duct up 2" before you exit teh building will again reduce your air noise. A fan sitting at the exhaust point will indeed sound like a high velocity fan running. Good luck and use your best judgment along with the ideas from others. Its your ass if you get caught so be smart with what you do.
Use as much hard duct as you can for smoother air flow and remember to seal the seams! Seams as in elbows that have pivots, once you get everything in place then seal all the little slide places. Hope that make sense, if not it will when you start looking at the duct work elbows and seams in long straight pipes.

 

[Albert Hofmann]

Here is a quick experiment for you...lay out 30-40' of duct (flex would be fine for this test) with average turns and bends. Now hook a vortex up so that it is blowing through the duct, and observe the amount of air comming out of the duct (considerably less than the fan is rated for) Now take the same duct and fan and suck the air through, observe the amount of air comming from the duct now (very close to the CFM that the fan is rated for) These inline fans pull way harder than they push and are more efficient doing so. As for blowing through a carbon scrubber at the end of this long run...it can be done, but is not ideal. It is always best to get the air scrubbed in the room before venting in case there is a pinhole leak somewhere in the ducting that odor could leak out.

albert

 

[DIGITALHIPPY]

ive never had too much problems with long runs. just make sure that there are a minimum of obstructions/bends in the lines

 

[Hawk]

Thanks for the discussion. I think I'm going to go through with this (I've already started buying shit!).

I looked at the rigid ducting parts at the hardware store today and it doesn't look too hard to work with. If I plan it out well I think I'll be able to use rigid pieces for nearly every part. 6' foot straight lengths and various elbows should do it I think. I'll pre-fab as many sections on the ground as I can. Apparently there is purpose made duct sealant/caulk available as well. So I'll use that at the joints. Probably tape to just to be sure.

Also, I'll be sleeving everything in R8 insulated flex duct. I got 100' of it for about $20 on a blow out sale at Lowes. Should be more than enough for a pair of lines. My attic gets HOT so I think the insulation makes sense. Quiet too. I test fit a 6' rigid section in the flex duct and it slid right in.

The bitch of it will be working up there during the install. Ladder access only, hot as hell, piss-poor footing (gotta find the 2x4's under the blown-in insulation). I'm not sure how I'll keep from smashing down the insulation were I'll need to work. Brush it aside and brush it back when I'm done, I guess.

The only thing I'm worried about is the attic temps and fan longevity/safety. Mostly safety (fire). My plan is to build a muffled box each fan will reside in. Outer layer to inner layer of the planned boxes: particle board, sound board, 1/4" drywall, and then fiberglass matting all around the fan. The sound board has NO fire retardation so that's why the drywall would be there. My hope is that when the fan is running the airflow through the fan will keep the motor temps in check. I figure the boxes should protect the fans from the high ambient attic temps. Even if the fans are off and the temps in the boxes equalize with the attic, as soon as they kick on the airflow should cool them down to nearly the same temp as the exhaust. And then the boxes will keep them from sucking up the attic's ambient temperature.

Does that all make sense? Any other ideas for overheated fan safety in a super hot attic?

 

[BudZad7]

Hi All! Nice Info!!! Here's a setup question???? 4x8 Habitat hut with intake vents 6" and exhaust vents 6" intake vent attached to 6" ducting from ceiling, and a 6" inline duct fan sucking air thru the ducting into the hut.....then
the exhaust vent has a 8"~6" reducer and 8" ducting 25' going to ceiling and a
Max fan 8" attached with a 6" carbon filter"Freshmaker" pulling air from hut into the attic....the side walls of the hut are being sucked inward like a vacume, but the Hydrofarm website shows a diagram of air flow for their huts....So, is the
above info a good setup?? Please help!!!! Peace!

 

[Hawk]

Update on my progress:

I've got one of the duct runs installed and functioning. The second run is mostly done but is not functioning yet. The duct run that's online is probably more than 50 feet end to end. That's starting at a (temporary) carbon filter made from a "blanket" of activated carbon filter material, ~4 feet of flexible duct, Super Sun 2, ~6 feet of flexible duct, then ~25 feet of rigid duct with 2 90deg turns, then ~3 feet of flex duct, then the fan, then another 10+ feet of flex duct. The flexible sections all have some mild to moderate turns. A good portion of the flex duct is temporary until I finalize the position of everything and get more rigid in there. Although it's tempting to leave it as-is.

It's all 6" and the fan is an EcoPlus rated at 440cfm. I wish I had a way to measure the airflow. It's hard to gauge. But my sense is that while I've certainly lost some CFM, the drop isn't as dramatic as I feared. It's still moving plenty of air.

I was careful about sealing up all the joints on the rigid section. Every joint got ducting caulk plus duct tape. Even the elbow sections got caulk where the sections spin to adjust the angle.

I learned a lot about doing a project like this. My plan of sliding my R8 insulated 6" flex duct over the rigid sections didn't work out as planned. I test fit a 6" pipe in the flex duct at the store and it slid right in. But trying to slide the insulated flex over a 25" run is a whole different ball game. And sliding it over the elbows doesn't work. I ended up separating the inner hose from the insulation sleeve and just slid the insulation on. That worked but was still hard. An extra pair of hands would have made a big difference for doing that part. Had I cut the insulated ducting to 5' sections to match the length of the rigid sections and connected it all one piece at a time might have been better.

The fan noise is almost non-existent inside the house. The fan is mounted in a multi-layered sound isolation box. The only noise is a slight reverberation noise coming down through the walls/ceiling. There's hardly any vibration to be felt when you place a hand on the box but whatever vibes are there seem to travel well. I believe some rubber feet (or something) mounted on the box will block the vibration from transferring down through the framing. But even as-is, it's acceptable and only audible if the house is completely silent. My refrigerator compressor completely masks it if that gives some sense of how much noise I'm talking about (fan is located above the kitchen).

Overall, it's working out well. It's been a major PITA to do (and expensive) but I believe it will be worth it in the end.