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AC Boxes Made Easy (to understand and build)

hoosierdaddy

Active member
ICMag Donor
Veteran
It's HOT and my plants need AC!

42896ac0-thumb.jpg

I have seen several tutorials here and on other forums on how to construct an AC box. Some of the tutorials available seem to be lacking very important points. In fact, I know for certain that some of the AC box tutorials are completely wrong, and will do nothing but cause the user problems, money, and a potentially ruined grow.

From what I have seen, the biggest problem AC box builders face is not knowing how the AC unit actually functions. I think that if many growers were to fully understand what the AC unit does, and how it does it, they would not have any troubles in constructing their own box. They would also be able to easily recognize the tutorials out there that are completely hosed up and should be disregarded.

I have actually tried to offer up some help with some of these AC box tutorials, but it seems that ego often trumps common sense, and some of these hosed up tutorial authors do not want to admit that they are putting out bad info.
Constructive criticism seems unwanted, even when heavily warranted.

If any grower sees a fault with my tutorial in any shape, form, or fashion please do not hesitate to bring it up for discussion. I have thick skin and have learned that the ego is something best left in your back pocket.
With all that said, let me continue with my presentation....




For this tutorial I am going to assume that you have chosen the correct size AC unit to fit your grow. Many factors can come into play when sizing the AC unit, and there are several tutorials available that give great info on figuring out the proper BTU size of the AC unit.
I am using a small 5000 BTU unit for this tutorial, which is what I am using for my cabinet mini-grow. I will go into my specific unit later...

Although this thread is not to show you how to pick the proper unit, I do recommend that growers use a manual controls unit if possible. Digitally controlled units can fail to restart properly if the incoming main power is ever shut off or lost for any reason. Manual control units will simply start to function normal again once the incoming power is restored. This seems like a small item, but it could potentially mean the difference between a nice harvest and a cooked, wilted out patch of nothing.
Manual controls units also make it easy to control using timers, and digitals may not actually give you that option.

There is lots of air movement going on with an AC unit.
42896ac1.jpg


There are two main areas of an AC unit. The compressor side (cold side) and the condenser side (hot side).
These two area are separate from one another and have independent air flows. The cold side of the unit recirculates air that is within the grow space. This air is cooled by sucking it through the compressor coils and then returning it to the grow space. A thermostat on the front of the unit controls when the compressor will run and create more needed cold air.

The hot side of the unit uses ambient air that is not associated with the cooled space. This ambient air is sucked through the condenser coils, which cools the refrigerant material that flows inside of them. This hot air is then exhausted to the atmosphere.
42896ac2.jpg

There are options with how to configure your AC unit air flow.
The unit can be used in the conventional fashion by having a hole in the side of the grow room that allows just the cold side of the AC unit. The remainder of the unit (hot side) is outside of the grow area. This is similar to how the unit was designed to function. In fact, if you have a window in your grow room, you can mount just about any conventional AC unit without using a box at all, as that is how they are originally designed.
But having a widow in the grow room doesn't happen often. So we need to have other options.

One is to simply cut a hole in the grow room wall and only allow the cold side in the grow. The hot side can be in another room, and it can draw the ambient air needed to cool the hot side coils from that room. Although you must make certain that the room itself can draw in fresh air for the unit to use.
So far we have not constructed any box at all, but we will now need one for the hot side exhaust. We cannot let the hot exhaust go into our ambient air room, as it will quickly heat up the air in the room, which will eventually cause the AC unit to overheat and fail.

The box will need to enclose the whole back end of the AC unit, as the hot coils are nearly that size.
There is a fan on the inside of the AC unit that normally blows the ambient air from outside through the hot side coils and out to atmosphere. When we mount up a box around the exhaust of the unit, we must direct the air out somehow. For this, ductwork of some type is needed.
42896ac4.jpg

Sizing of this ductwork is of the utmost importance. The internal AC unit fan is blowing air at X amount of CFM through a fixed port size. Any time we restrict the size of the originally intended air flow, we jeopardize the integrity of the unit.
The vents in the side and top of the AC cover have provided adequate opening for the proper amount of ambient air to enter the unit. And as long as you do not choke down the air flow path downstream from the fan, then the unit will function properly.

If we kept the back end of our exhaust box open, and elongated the box until we reached an opening to the outside, then we would need no additional fans or ducting to exhaust the air properly. The problem is that this is often not a feasible thing to do.
So, we most often time depend on duct work that we add. The most common being 4" and 6" flexible ducting. Flexible ducting is one of the worst types of ducts we can use for air flow concerns, as that type of duct has a very large friction factor and can easily cut your airflow in half by simply making a turn.

Now, we can overcome the shortcomings of the smaller duct work by adding an additional fan that will assist with the air flow, or we can figure out what size duct we need to handle the air as normal.
One way to see if you have enough exhaust ducting is to take the AC unit cover off and measure the enclosure that surrounds the exhaust fan. This enclosure can be considered a duct, as it is the bottleneck of the AC unit's air flow. If your ducting is as large or larger than this enclosure around the fan, then you should be fine without an additional fan. But it is very seldom you will see folks running 10"-12" ductwork for AC boxes. Which is what even the smallest AC unit enclosure fan is going to be within.

OK, we have decided to use 6" flexible ducting and an additional fan to pull the air out of the box.
42896ac3.jpg

There is another option that can allow you to place your AC unit right inside of your grow room. However, we must do some work to make this happen. The ambient air that is used by the hot side to cool the coils should NOT be taken from the cool air grow room. This is a gross waste of energy and the cold air you spend money to create will simply be blown back out the exhaust. Eventually leaving you with a hot room and a failed AC unit. Not to mention that there is no oder control using this method, and the funk will find it's way out the exhaust.

What we need to do is to manipulate the incoming ambient air. To do this we construct another box around the ambient air vents, and duct this box to the outside so the unit can have fresh air.
42896ac5.jpg

You can build the box so that it completely encloses the intake air vents as in the previous sketch, and then run your duct to the outside.

You can also build a smaller box that only encloses one of the vents on the unit cover. The other incoming vents must be taped up and blocked off.
Thing is with this method is we run the risk of providing too little ambient air to the unit. If you choose to only duct in to one vent, make sure you snip the vent metal of the vent you are using so it opens it up. As long as you have the rectangular vent opening the same size or larger than your incoming duct, then it should be fine.
42896ac6.jpg


Again, if you have sufficient air flow area with your exhaust box, then you are going to also have to have sufficient air flow area with your incoming box as well...to get by without additional fans. However, since we normally will not have the correct size ducting, an additional fan is almost always warranted.

This additional fan can either be pushing on the intake side of things, or pulling from the exhaust side of things. Or both. The size of the ducting and fans are for another tutorial. Again, I am assuming you have these items worked out.

A free standing unit inside your grow room would look something like this:
42896ac7.jpg
Note that we now have TWO separate boxes. And for a word of advice, any tutorial that has you totally enclosing the whole back end of the unit, including the exhaust and the intake vents, is a NO GO. It may look nice and fancy, but it will NOT WORK PROPERLY, let alone efficiently.
If someone tries to convince you this will work, ask any HVAC man and see what he says. I guarantee it is a mistake to try it.

I realize that many simply do not have the tools or ability to build fancy boxes with wood. It can be a very daunting task for those who have never tried such work. But, there is an alternative.
I like to use aluminized foam insulation board. This stuff is very, very light weight, very easy to work with, and needs no special tools, save for a carpet knife, some duct or aluminum tape, and a ruler.
My product of choice is Dow Corning Supertuff R. This material is not only going to make it easy to build any sort of box you want in no time flat, it also is a great insulator and will not let the excess heat from the exhaust heat up the room. It also serves a decent sound barrier. Just remember to also wrap insulation around your flex duct if ambient heat is a concern.

Most AC units have a drain to get rid of the built up condensation that the condenser coils create when cooling them with the rush of air. You will need to compensate for the drain you have an run it to a safe runoff.
Some units are evaporative, and will not have a drain. These units will normally rely on the air movement to re-evaporate the condensed water back to the atmosphere. These types of units were designed to have the back end outside, and may not do what you think they will with the water. I suggest that you make a way to access the bottom of the inside of your unit so that you can periodically get the water out. I use a turkey baster to do this, and I have never had to take out more than an ounce of water or so from my evaporative unit. When the RH is low, the thing runs nearly bone dry.

I hope that this tutorial will be of help to fellow growers.
If you have any questions or concerns, please don't hesitate to post them up.
I will try my best to address any all questions. Or, I will try to get the right person involved that can clear up any cloudy issues for us.

Overgrow the world, and stay COOL!
:pimp3:


Oh yeah...my AC unit!

I have a 5050 BTU AC unit mounted inside my cabinet. The thing works like a charm and I have had no problems at all.
Air enters my veg chamber and flows through to the ambient air intake of the AC unit.
42896cabac01.jpg


The ambient air is then run sucked through the hot side coils and exhausts the hot air out to duct work that leads to a DIY Stanley blower in the attic.
42896cabac02.jpg

The cool side of my unit is in the flower area and is separated from the ambient and exhaust flows.
42896cabac03.jpg
 

kb5178

Member
Thank you for the great tutorial,and sorry for the jump to conclusion on who you are in the GW thread.Peace to you and your's brother KB
 

hoosierdaddy

Active member
ICMag Donor
Veteran
Hey, Liam. Those misters can work fine for an outdoor set-up, and were specifically desingend for central air units. They could be incorporated into an AC box situation, but the moisture control may end up making it a wash, forgive the pun. Those things will put out a tremendous amount of water in no time.
I suppose if a man were to want that sort of apparatus, he could incorporate a catch barrel and use the water for feed stock.
Thanks for stopping in and taking a look.

It's all good, kb5178
 

FreezerBoy

Was blind but now IC Puckbunny in Training
Veteran
Kudos for your fine tutorial! Makes me want to build one and I don't even need it.

 

Liam

Active member
Well, my AC at the time couldn't keep up to the heat, and I needed just a few day fix before I would buy another. So I sprayed water on the radiator with a spray bottle every hour or so... works well because the water evaporates cooling even more so than the coldness of the water.

Give it a try, I was impressed how well it worked... forgotten about it till I saw ur thread, I never even thought of making an AC box...
 
G

Guest 18340

Great tutorial! Well detailed and easy to understand. 2 thumbs up bro :yes: :yes:
 

NorCalFor20

Smokes, lets go
Veteran
exellent thread, you really break down the process for non-diy'ers like myself

I may be able to make a box after reading through this one. K+
 

hoosierdaddy

Active member
ICMag Donor
Veteran
FreezerBoy....LOL! (I can relate, it's the tinker in us)

I appreciate the props, Pharma!

Thanks for stopping in and the kind words, Elvlme2!

NorCal20...you need to know that I had you in my mind while I was doing this tutorial.
You have the identical unit to mine I think. (Samsung?)
I have wanted ever so badly to make a comment, but you seem to be dealing so I didn't. I hope very much that you can get some good use from this thread.

Peace, y'all.
 

eyes

Active member
Veteran
Hey Hossierdaddy,very good tutorial.Whats the chance we can get some actual pics of the a/c in action in the cab?
 

hoosierdaddy

Active member
ICMag Donor
Veteran
Thanks mucho, JT!

Thanks for taking a look, eyes.
You can see the evolution of my cab at:
http://www.icmag.com/ic/showthread.php?t=84904&page=1&pp=15

42896cab3.jpg


This is just after I roughed the AC unit in. Only thing changed is I taped it up better.
42896Photo_070208_005.JPG


The top temp is ambient in the garage, bottom temp is remote sensor in the cab at the top of canopy.
At the root zones the temp is about 67-69degF.
42896Photo_070408_001.JPG

I just looked and the ambient temp outside the cab is 87degF inside 74degF.

The airflow that I have seems to split my flower chamber into two basic zones. The upper stays between 75-85degF and the lower is always 67-69 lights on or off.
I keep the controls at about half.
 
Last edited:

OgreSeeker

Active member
hoosierdaddy said:
It's HOT and my plants need AC!

42896ac0-thumb.jpg


There is another option that can allow you to place your AC unit right inside of your grow room. However, we must do some work to make this happen. The ambient air that is used by the hot side to cool the coils should NOT be taken from the cool air grow room. This is a gross waste of energy and the cold air you spend money to create will simply be blown back out the exhaust. Eventually leaving you with a hot room and a failed AC unit. Not to mention that there is no oder control using this method, and the funk will find it's way out the exhaust.

What we need to do is to manipulate the incoming ambient air. To do this we construct another box around the ambient air vents, and duct this box to the outside so the unit can have fresh air.
42896ac5.jpg

You can build the box so that it completely encloses the intake air vents as in the previous sketch, and then run your duct to the outside.

You can also build a smaller box that only encloses one of the vents on the unit cover. The other incoming vents must be taped up and blocked off.
Thing is with this method is we run the risk of providing too little ambient air to the unit. If you choose to only duct in to one vent, make sure you snip the vent metal of the vent you are using so it opens it up. As long as you have the rectangular vent opening the same size or larger than your incoming duct, then it should be fine.
42896ac6.jpg


Again, if you have sufficient air flow area with your exhaust box, then you are going to also have to have sufficient air flow area with your incoming box as well...to get by without additional fans. However, since we normally will not have the correct size ducting, an additional fan is almost always warranted.

This additional fan can either be pushing on the intake side of things, or pulling from the exhaust side of things. Or both. The size of the ducting and fans are for another tutorial. Again, I am assuming you have these items worked out.

A free standing unit inside your grow room would look something like this:
42896ac7.jpg
Note that we now have TWO separate boxes. And for a word of advice, any tutorial that has you totally enclosing the whole back end of the unit, including the exhaust and the intake vents, is a NO GO. It may look nice and fancy, but it will NOT WORK PROPERLY, let alone efficiently.
If someone tries to convince you this will work, ask any HVAC man and see what he says. I guarantee it is a mistake to try it.

I realize that many simply do not have the tools or ability to build fancy boxes with wood. It can be a very daunting task for those who have never tried such work. But, there is an alternative.
I like to use aluminized foam insulation board. This stuff is very, very light weight, very easy to work with, and needs no special tools, save for a carpet knife, some duct or aluminum tape, and a ruler.
My product of choice is Dow Corning Supertuff R. This material is not only going to make it easy to build any sort of box you want in no time flat, it also is a great insulator and will not let the excess heat from the exhaust heat up the room. It also serves a decent sound barrier. Just remember to also wrap insulation around your flex duct if ambient heat is a concern.

Most AC units have a drain to get rid of the built up condensation that the condenser coils create when cooling them with the rush of air. You will need to compensate for the drain you have an run it to a safe runoff.
Some units are evaporative, and will not have a drain. These units will normally rely on the air movement to re-evaporate the condensed water back to the atmosphere. These types of units were designed to have the back end outside, and may not do what you think they will with the water. I suggest that you make a way to access the bottom of the inside of your unit so that you can periodically get the water out. I use a turkey baster to do this, and I have never had to take out more than an ounce of water or so from my evaporative unit. When the RH is low, the thing runs nearly bone dry.

I hope that this tutorial will be of help to fellow growers.
If you have any questions or concerns, please don't hesitate to post them up.
I will try my best to address any all questions. Or, I will try to get the right person involved that can clear up any cloudy issues for us.

Overgrow the world, and stay COOL!
:pimp3:


Oh yeah...my AC unit!

42896cabac03.jpg




Alright man! I was wondering when you were gonna get this up!!
When I first started reading through your thread I was hoping that you would mention the option of putting the entire ac into the room (which is necessary for many of us) and draw up a sketch. GOOD DEAL!!!
+rep


**edit**

One thing that I want to mention for anyone reading this.

1. Two boxes are not required for the fully enclosed option. My brother in law is running an ac box right now that has the entire back end enclosed (one duct in, one duct out) and it runs perfectly. No extra cycling, no jump in electric usage (except for the large fan he uses) and it cools his room same as it always did.
It will work fine and has been done many times by many other members here as long as your pulling enough CFM.
 
Last edited:

hoosierdaddy

Active member
ICMag Donor
Veteran
OgreSeeker said:
**edit**

One thing that I want to mention for anyone reading this.

1. Two boxes are not required for the fully enclosed option. My brother in law is running an ac box right now that has the entire back end enclosed (one duct in, one duct out) and it runs perfectly. No extra cycling, no jump in electric usage (except for the large fan he uses) and it cools his room same as it always did.
It will work fine and has been done many times by many other members here as long as your pulling enough CFM.
I know that many have done that, and it works for them. But I guarantee it is not performing as efficiently as it could with separation of air flows.
 

OgreSeeker

Active member
Yeah I plan on building mine with two separate boxes and use insulation board rather than a single wooden box.
Hey man what do you use to draw up those plans? Those sketches are pretty slick!
 

hoosierdaddy

Active member
ICMag Donor
Veteran
Those were with Autosketch. It's an old windows based Autodesk (Autocad) product.

I copy them as bitmaps from the sketch program, then make jpgs out of them in paint when I am done.
 
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