AC Boxes Made Easy (to understand and build)

[DenseBuds]

Thanks. No way I can keep the ducting the same size as the ac fan. If I all of a sudden had a 12"+ vent on the side of my house, it'd draw too much attention. 6-8" is my max.

 

[Gold123]

Thanks. No way I can keep the ducting the same size as the ac fan. If I all of a sudden had a 12"+ vent on the side of my house, it'd draw too much attention. 6-8" is my max.

why not put the ac in the wall and duct the cold air to the grow?

 

[DenseBuds]

why not put the ac in the wall and duct the cold air to the grow?

I'm not confident I can mount it properly and I don't want to be in a position where I cut a big hole in the wall and have issues. I've put in exhaust vents before though.

 

[louie]

Hoosierdaddy awesome thread man! So I just bought a 15,000 btu AC and am going to run it in a room I built inside a bigger room. I plan on cutting a hole in the wall of the smaller room and mounting the AC in the wall and directing the AC cold air into the small room (somewhat sealed) and have the back hang out into the bigger room. I was going to build a box on the outside of the AC to vent the hot air outside. I plan on using 6" ducting because I already have a bunch and because I wont be able to build a box that leads all the way outside (its like 10 ft, so ducting is the only option). My question is what size fan should i use to assist in ducting the hot air outside? I have a 465 cfm squirrel cage, and an 8" vortex (pretty powerful) laying around I could use. Thanks man

 

[hoosierdaddy]

A 15k unit is going to push lots of air out the back to keep the coils cool. I suggest taking the cover off the unit and having a good look at the fan in the back. It will probably have plastic that surrounds the fan blades and the coils. The diameter of the plastic around the fan can be looked at as a duct of sorts, in that it meters how much air moves through the coils. Now, if there is no restriction, the units fan alone is enough to keep the unit cooled.

But let's assume that the fan is blowing through plastic with a diameter of 12". If you choke it down past the back to a single 6", you will have really restricted the air flow, and the fan will not be enough to move the proper amount of air...so you will need to add a fan to be able to suck enough air to keep the coils cool. Now, what this means is that the only way you can get the old volume of air back once you choke it down, is to run a fan real fast so it can pull more air. And with a single 6" duct and fan, you probably aren't going to have the CFM to do the job. I would suggest adding both the 6" and the 8" together to pull on that unit. Use 8" duct for the bigger fan.

Now, if your internal room were only 8ft from the other wall, a single piece of dow corning supertuff R would probably be all you need to make a square duct (the size of the back of your ac) and run it through the same size hole in the outer wall. You would need no extra fans doing that, and the board is only like 12$. Roll of aluminum tape to put it together another 10$.
If it is 10 ft...you would still be better off buying another piece of board and add two foot for less than it would cost on equipment, electric, noise, and life of ac unit if you run ducts and help with fans.

 

[greenhornets]

bump

 

[louie]

A 15k unit is going to push lots of air out the back to keep the coils cool. I suggest taking the cover off the unit and having a good look at the fan in the back. It will probably have plastic that surrounds the fan blades and the coils. The diameter of the plastic around the fan can be looked at as a duct of sorts, in that it meters how much air moves through the coils. Now, if there is no restriction, the units fan alone is enough to keep the unit cooled.

But let's assume that the fan is blowing through plastic with a diameter of 12". If you choke it down past the back to a single 6", you will have really restricted the air flow, and the fan will not be enough to move the proper amount of air...so you will need to add a fan to be able to suck enough air to keep the coils cool. Now, what this means is that the only way you can get the old volume of air back once you choke it down, is to run a fan real fast so it can pull more air. And with a single 6" duct and fan, you probably aren't going to have the CFM to do the job. I would suggest adding both the 6" and the 8" together to pull on that unit. Use 8" duct for the bigger fan.

Now, if your internal room were only 8ft from the other wall, a single piece of dow corning supertuff R would probably be all you need to make a square duct (the size of the back of your ac) and run it through the same size hole in the outer wall. You would need no extra fans doing that, and the board is only like 12$. Roll of aluminum tape to put it together another 10$.
If it is 10 ft...you would still be better off buying another piece of board and add two foot for less than it would cost on equipment, electric, noise, and life of ac unit if you run ducts and help with fans.

I really appreciate the help man! Now I just mounted the AC last night. It is mounted in the wall of the grow, blowing cold air inside. I plan on building the box tonight with the insulation board. I am planning on using the 8" 747 cfm vortex fan to exhaust the heat from the AC outside via 6" hosing which will be hooked up to a 6" vent that already exists in the house. It would be optimal to to 8" ducting off the fan though. I was thinking of ways to exhaust using the 8" ducting, but I am kind of stumped. If I use the 8" ducting off the fan and then reduce it to 6" right before it exits the house that would be the same as reducing to 6" ducting straight from the fan, right? The only other thing I can think of is cutting a hole in my furnace exhaust and exhausting into that with the 8" ducting the whole way, but don't really want to because: a) don't want to have a hole cut in the furnace ducting and b) don't want to have the chance for even a small leak in the connection of the furnace ducting and possible AC exhaust because of the chance of having Carbon Monoxide and other harmful gases leak into my living space. What do you think?

 

[hoosierdaddy]

You are correct in that if you go through a 6" at any point, you might as well have 6" inch all the way. The flow can only be figured using the smallest orifice in the line.

Give it a go. The unit will more than likely let you know if it isn't enough air movement.

Units that size will often have a fresh air vent feature. You must make sure that is glued shut and caulked if need be to keep the cool air and the funk in the grow.

 

[louie]

You are correct in that if you go through a 6" at any point, you might as well have 6" inch all the way. The flow can only be figured using the smallest orifice in the line.

Give it a go. The unit will more than likely let you know if it isn't enough air movement.

Units that size will often have a fresh air vent feature. You must make sure that is glued shut and caulked if need be to keep the cool air and the funk in the grow.

So this fresh air feature, where is it located? I have the new 15,000 btu LG window model. Will it say anywhere if it does have this feature? How does it work?

 

[hoosierdaddy]

One of the controls may say "VENT" on it. When engaged, it will open a door withing the unit that allows air coming in from the rear intake to mix with the cool air.

All window ac units have a chamber that the cool air circulates though. This is where the cold coils are that cool that air. This chamber can have a door on it on the inside of the unit.
You would need to take the cover off the ac to see this.

 

[GMax]

dude hoosier i just wanna personally thank you for the awesome thread. you literally saved my crops I did the whole portable ac thing last summer and that thing was a pain in the ass. DO NOT BUY ONE OF THESE they are impossible to get smell free AND enough airflow and when i dusted it off this summer it was aready out of freon!! what a waste of $300. anyways i run a vertical aero system and for the last straight week my plants been sitting in 95 degree canopy 86 degree water temp !!!!!!(yeah i know crazy right) i guess i can thank SM-90 too cause my roots still nevr looked heathier (miracle product in my eyes) and a lil silica but after reading your tutorial got myself a lil 5000 btu and some 10 inch ducting now i am sitting in 76 degree and i can walk in my flower room without sweating like a hog. so thanks again it was way easier to build than i thought and it was half the cost of a portable ($170 total with ac being $99) and cools 3x better than a portable of twice the power. great job dude my plants thank you

 

[Tactical Farmer]

Im working a plan for summer cooling - first planned to use the roof vent ports to pull air in through the attic via 6 in duct to room.

But during the day when the roofs hot will it make the heat problem worse ?

Bad place for summer intake right ?

Should work well in reverse for venting at least.

 

[hoosierdaddy]

Man, that is great news, GMax!
I am so glad it worked out for you. I know I wouldn't be able to grow in my hot garage without mine.
I just now checked temps...
79F ambient garage air
70F floor of cab
74F 4" into canopy
86F top of cab at exhaust

Those last three temps will stay about the same with the first temp being as much as 90-95. When it gets real hot like that I need to turn it up to about 8 or so to keep up. But like now it is only set on 4-5 and only comes on occasionally.

Pass on the knowledge!

 

[hoosierdaddy]

Im working a plan for summer cooling - first planned to use the roof vent ports to pull air in through the attic via 6 in duct to room.

But during the day when the roofs hot will it make the heat problem worse ?

Bad place for summer intake right ?

Should work well in reverse for venting at least.

If you use insulated ducting it won't heat up the air more than it was at intake. Although on top of a black roof can be a real hot place for air to come from. Best if you can get it from a shaded area, or from the soffet, or even a gable vent area. But if all you can do is pull it from the roof, that works. But, I do agree that it would help to heat the air in the duct up if it were not insulated. You might get 100degF air from the roof on a hot day, but the air under the roof may be 120-140 degF.

FWIW, if I were to take the time to do a proper hole and stack, I would go bigger than 6". I want as big as I can manage for intake.

 

[Tactical Farmer]

that was quick thanks - there just doesn't seem to be just 1 perfect setup here, going to need multiple configurations for different times of the year.

 

[bs0]

What about a 4" inline fan for the back half? What do you construct your chambers out of?

Great thread, this dual hose A/C is not doing the job I expected for $600. Gonna have to look into this more.

 

[Tactical Farmer]

Dang it - Some crappy reviews on most of the A/C manufactures, cant even use the warranty if its all chopped up.

2 questions:

1. any reliable brands that stand out or are they all re-named China junk now ?

2. Can the rear shell be removed & custom box be fitted ? (could undo & return to normal for a possible failure return)

Thanks again - Great thread

 

[hoosierdaddy]

4" duct is not enough intake air to satisfy the hot side coils.
It is a good rule of thumb to have approx the same amount of intake area as the area that surrounds the fan in the back of the AC unit. The casing around the fan is a duct of sorts and dictates how much air it wants. If that plastic is 10" in diameter, you need to feed the back of the unit with a 10" duct, or a combination of smaller ducts that equal the intake area or greater.

TF,
No idea of brands..probably all chinese specials. (shrug)
I suggest fitting a box around the existing back like in the tutorial. Much easier than building another from scratch. You can attach it with duct tape.
It is always much better if the back of the unit is in an area that it can just suck up the ambient air without needed ducts feeding it, then box up and duct out the hot air.

 

[bs0]

4" duct is not enough intake air to satisfy the hot side coils.
It is a good rule of thumb to have approx the same amount of intake area as the area that surrounds the fan in the back of the AC unit. The casing around the fan is a duct of sorts and dictates how much air it wants. If that plastic is 10" in diameter, you need to feed the back of the unit with a 10" duct, or a combination of smaller ducts that equal the intake area or greater.

what i meant was a 4" inline fan like a 4" vortex (like 260cfm or so) and do forced air movement on the exhaust... is there any negative to supplimenting the split a/c's exhaust by adding a duct fan? more airflow could mean increased cooling efficiency?

 

[hoosierdaddy]

If you are asking about a split unit, I can only tell you that you can increase the air flow by increasing cfm, so yes it would help on those types of units...I think...I don't use them and not familiar with the unit you are speaking of. I assume you are talking about installing the fan in the existing exhaust line?
Not really clear on what you are trying to do.
Maybe you could sketch it out?