Vent size and building stability question

[Ref1]

Hello,

I have a question about vent size. I read Vent101 but I want to make sure I get everything right or at least close to right.

I am in the process of building 13x15 room with 6K Gavitas. I have 24,000 BTU AC in there but I want to have a regular exhaust just in case my AC goes to sleep. The room will be in the basement and I want to run exhaust pipes in between floor joists. I have room for 7" pipes (sheet metal). I want to run these pipes outside and I would have to cut an 7" hole in the exterior wall but I am afraid that there will be nothing much left. The opening between the floor joists is 7" tall by 14" wide. Would there be a problem if I cut 7" round hole?

Another question is size itself. My room is 1560 CF and I have Hyper Fan Stealth 10" rated for 1065 CFM. So I figure that that should be enough for this room to have air exchanged every minute and a half. Well, lets say every 2 minutes with carbon filter which is 10"X39" Phresh Filter rated at 1400 CFM. So if I have to downsize my duct to 6" sheet metal pipes, would I still have adequate air movement to cover me in case my AC fails?

Thanks you all in advance and please excuse me if I am not expressing myself correctly as English is my second language.

Peace,

Ref1

 

[corky1968]

13' X 15' is a very odd size.

Can you by any chance go 12' X 16'?
This would be so much easier to build.

Reason: They sell 8',10'.12' and 16' lumber.

Sticking with industry standards will save you lots of headaches, save you money and generate less waste.

 

[Ref1]

13' X 15' is a very odd size.

Can you by any chance go 12' X 16'?
This would be so much easier to build.

Reason: They sell 8',10'.12' and 16' lumber.

Sticking with industry standards will save you lots of headaches, save you money and generate less waste.

Yes, it is odd and generated some waste, but mostly from drywall. it's being built in one half of the basement, and size is 13 ft wide by 30 ft long. I split that in 3 rooms and have dedicated 13 x 8 for mother/veg area(1 4x8 tray and mothers with clone area), 13 x 15 bloom (3 4x8 f/d trays) and 13 x 7 for utility/storage. I have 36" doors and they are right by the wall apprx. 3 inches off the wall so I can have my trays right next to each other like Gavita rep recommended for better light spread and still have some room to work around it and for placing CO2 generator, scrubbers, fans and water intake/outtake pipes.

I learned a lot of new things in this build and I would've done some things different now since I have an experience, because I had to do it all by myself due to security reasons. But, it is half way finished now and no turning back.

I will post progress pictures in the future when it's finished and when I learn how to do so securely.

Appreciate any feedback.

Thanks,

Ref1

 

[corky1968]

The best way to learn is to do things by yourself after you've checked out other people's ideas.
This way any mistake made the 1st time around will really stick into your mind whenever you do
approach the same problem. Getting other people to do everything for you doesn't really get you
anywhere in life.

Bring on the pics when your ready.

 

[Punisher 421]

I'm sure u can find the information you're looking for if you do a Google search on "duct calculator". I'm an hvac guy and I have one that u input room size and equipment size and it tells u minimum duct size so I'm sure u can find an online version. Good luck, hope this helps

 

[Ref1]

I'm sure u can find the information you're looking for if you do a Google search on "duct calculator". I'm an hvac guy and I have one that u input room size and equipment size and it tells u minimum duct size so I'm sure u can find an online version. Good luck, hope this helps

Thank you for a reply.

I just did a search and I came up with multiple options and some of them require velocity speed and velocity pressure. I am not sure where to get these numbers.

I found one and asked for ft/min input and duct size so when I put 1065 for my fan cfm and 7" for duct I came up with 285 number. I believe that's 285 cfm with that duct size, correct?

 

[Ref1]

Also I am still wondering if I can cut a 7" hole in the wall. I hope its not structurally damaging.

 

[Ref1]

I was also thinking about going with rectangular duct. Let's say 12x6. Would that be sufficient?

 

[Ref1]

on one site I found that 7x10 rectangular duct equals to 9" round duct. and that should give 1000 CFM. I am going to have this custom made though. Anybody see any problems with this?

I will be posting pictures soon. I estimate to have this finished in 3 weeks tops.

 

[Granger2]

Use straight duct pipe wherever possible. Cheaper, better air flow than flex duct. What you're talking about cutting shouldn't be a problem structurally as long as you're not cutting load bearing material like studs, rafters, beams, etc. Good luck. -granger

 

[Punisher 421]

Yes the 285 is cfm. U can use any of the options u talked about.

 

[Ref1]

Use straight duct pipe wherever possible. Cheaper, better air flow than flex duct. What you're talking about cutting shouldn't be a problem structurally as long as you're not cutting load bearing material like studs, rafters, beams, etc. Good luck. -granger

Thanks G2.

I am glad to know I can proceed. Can't wait to finish and start growing again.

I get all duct in sheet metal too. I had a bunch of flex duct from my tent grows but this time I want to do everything right.

 

[Ref1]

Yes the 285 is cfm. U can use any of the options u talked about.

285 isn't much.

Well, its decided. I will get custom made rectangular 7x10 duct

 

[booghy]

Slightly off topic.....but what's ur height? I've heard the Gavitas need a lot of head room to operate. You said basement and most don't have more than 7/8' height.

 

[Ref1]

Slightly off topic.....but what's ur height? I've heard the Gavitas need a lot of head room to operate. You said basement and most don't have more than 7/8' height.

My basement is 8 ft. I will use flood and drain tray on the floor with reservoirs dug into the ground for more head room and geothermal climate control. My ceiling is insulated with automotive reflective heat shields that withstands 2000 degrees. Light movers are installed in between the joists to help with height. They will be moving only for 1 foot to help with the hot spot. My friend also got me a new gavita w150 reflector that is supposedly made for lower heights. It has 150 degree throw (wider than usual) and doesn't have such a bad hot spot as the regular reflector. I usually keep my canopy no higher than 3 feet off the floor. 1 ft for lamp itself which will be in between floor joists, and it leaves me with another 5 feet of head room. I will need only 3 feet as I will be running them at 1000W. I doubt I will boost them to 1150 but I will see how it goes along my AC.

My friend that gave me those wide reflectors runs his Gavitas at 1150W 3 ft off the canopy with great results, constantly pulling 3.3+ per light. He emphasized on light movers. It is a must, otherwise risk a hot spot right underneath the lamp. He has 6000 BTU's of cooling per light though.

 

[Mikell]

Wow, this sure sounds expensive. As does a lot of what's being bandied about (2000* heat shield).

What's wrong with rigid round? There's nothing in a framed house you can punch a seven inch hole through that isn't plywood wall or roof sheathing.

High temp shut off's? Seems simpler.

 

[Ref1]

Wow, this sure sounds expensive. As does a lot of what's being bandied about (2000* heat shield).

What's wrong with rigid round? There's nothing in a framed house you can punch a seven inch hole through that isn't plywood wall or roof sheathing.

High temp shut off's? Seems simpler.

According to HVAC calculators 7" round would only allow 285 cfm. Not enough for proper air exchange. I want to cool the room with fresh air during the colder times of the year. Which is a good half at least. Will save me 2000+ watts coming from an AC. I got an estimate already and it will cost me only $310 for both room air exchange and window AC ducting to the outside. Not having to turn my AC for 2 months will pay that amount and then clean saving after that.


I also have gavita EL2 controller that would serve as high temperature shut off but I don't want to miss a beat in case my AC takes a shit. It will switch to air cooling right away. The problem is replacing AC if it takes a shit. I would have to coordinate with a family member to help me bring it inside because its heavy. And that would take a good 2 days. This way the grow will keep going on air exchange.

 

[Mikell]

Can't have too many back ups I suppose.

What about just using the joist space? Like tinbangers do. This would allow for a much more creative exhaust if you're cutting into a joist butt plate or whatever those are called.

Just spitballin'. I didn't intend to sound like such a dick with the first reply but I naturally am one.

 

[Ref1]

Can't have too many back ups I suppose.

What about just using the joist space? Like tinbangers do. This would allow for a much more creative exhaust if you're cutting into a joist butt plate or whatever those are called.

Just spitballin'. I didn't intend to sound like such a dick with the first reply but I naturally am one.

That's exactly what I am doing. My joist space is 14 X 10" but 12" X 6" duct is suffice for my needs if the need arises. It will only be used at night to remove humidity and once during the lights on. I know there are 2 camps about "sealed" and "semi-sealed".

I prefer "Seal-On-Demand" method.

I used to have a bottled CO2 in my last grow room but it was becoming expensive and I was running out of places to have it filled without suspicion. Installed CO2 generator and started having problems. Then switched to NG and it didn't help. Then I cut a 6" holes to bring in fresh air at night and once a day and plants haven't looked better, but that's for another subject.

And regarding butt plate. I have to cut through it to get my exhaust outside. Actually I am going to have 4 cuts. One in/out for grow room and one in/out for my AC (modified window banger)

 

[Ref1]

I have another question to the HVAC pros.

I have a 10" ducting and it's rectangular equivalent (12x6) and I want to use motorized dampers. I have 10" and 12" round Durazone dampers.

Question: Since inside flap of the damper may cause flow obstruction, should I use 12" damper with 12 to 10 reducer to increase flow?

Or is it unnecessary? Would that change in size ducting cause unwanted static pressure?