Cooling question. Window AC overheating.

whatapothead

whatapothead

Well-Known Member
ok heres the deal. got a shop.

just got a 25000 btu AC unit for it.

its a window style AC but i have it mounted in a 4x4x8' insulated box.

problem is i only have 4" insulated ducting running the 30 feet to the exhaust out the shop. i have a 6" 495cfm fan pushing the air out. with a stanley blower pushing air from outside the box into it.

the box is getting waaaay too hot and the AC is shutting down and only the fan runs after about 10 mins of running.

my question is.... if i run 8" ducting the 30 feet out of the shop will 495cfm be enough to cool this box?

or is my only/best bet to cut a hole in the shop, put a header in and mount it in the wall above the door. if i do this i take the risk of the owner wanted to come in and take a look at my install job.... which can't happen.
 
tilemaster

tilemaster

Well-Known Member
ahh ur tryn to vent a window a/c unit a very large one at that inside the shop thro a 30 foot run , instead of directly out the window? ya thats a tough 1. there not designed to have a box built around them if thats the case. although u can make a makeshift exhaust like u say and rig it to a inline fan ...but that seem like a lot of work opposed to a portable a/c. unless of coarse portable out of question cause u need 25,000btu for ur application. if that the case, ur gonna just have to get a ductless spit a/c unit. or another cooling method altogether

but ya try the 8'' duct and see if that works....just dont let that a/c unit fry bro. i had something very similiar going on my last grow. window a/.c unit inside my damn garage. made it feel like a sauna sound like a jet
 
S

somebody041

Well-Known Member
tilemaster said:
ahh ur tryn to vent a window a/c unit a very large one at that inside the shop thro a 30 foot run , instead of directly out the window? ya thats a tough 1. there not designed to have a box built around them if thats the case. although u can make a makeshift exhaust like u say and rig it to a inline fan ...but that seem like a lot of work opposed to a portable a/c. unless of coarse portable out of question cause u need 25,000btu for ur application. if that the case, ur gonna just have to get a ductless spit a/c unit. or another cooling method altogether

but ya try the 8'' duct and see if that works....just dont let that a/c unit fry bro. i had something very similiar going on my last grow. window a/.c unit inside my damn garage. made it feel like a sauna sound like a jet
Click to expand...
you need to have a seperate intake/exhaust. cover the side vents with duct tape and make a seperate intake box for the top of the window AC. then make another exhaust box around the back of it. both should be made of insulated board to help keep heat in control. then just stick your front plate in the cab.

also you are probably going to need a supplemental fan to help with the airflow if you are using 6 or 8" ducting.
 
Green Cross

Green Cross

Well-Known Member
whatapothead said:
somebody041 check ur pms!!!

anyone else have any knowledge of venting a window AC NOT in a window?
Click to expand...
I have an A/C window unit (mod) in my grow 150 CFM Dayton takes care of a 5000BTU.

As others have already pointed out your 25,000
BTU is a beast.

#1 ventilation rule - don't skimp. If you're looking to push 500 CFM through a 30' run of flexible duct I assume (less airflow)? take a look at the size of the blower in your a/c unit. 14" fan?


You need a beast of a blower to exhaust that bad-boy and large duct size. I would go with 12" duct and a Dayton Blower 549 CFM, but still not sure that will be enough.

Another problem I see is that 4 x 4 x 8 room you have the A/C venting into. You're better off building an insulated box that fits tight on the back of your unit. you can also restrict some of the air flowing in on the sides of the unit (by using some tape) - this will be like putting a governor on it, but it will also be less efficient.
 
morrisgreenberg

morrisgreenberg

Well-Known Member
do not tape any intakes closed, the top and side vent need whatever ambient room air it can get, i use 12k's and built and a/c box, just make sure the hot exhaust out the back does not interfere with the side vents on the a/c, the key here is duct size, i use 6in but thats the absolute minimum, if you can get 10 or 12, use that same fan, actually you may not need a fan since that a/c is blowing hard. i use a 250cfm duct fan and the flex duct gets very hot without the fan, with fan cool to the touch...so in essence you need larger ducting. with the a/c box(make sure you foam seal all around for leaks) you just made that window unit a portable and whatever radiant heat comes from the ducting just deal with it. the a/c will work really hard and hot if you dont seperate rear exhaust from side vent intake, the less restricted the air flow the better, its not perfect but this method is very popular and for me its a life saver
 
whatapothead

whatapothead

Well-Known Member
ah its not a 4x4 room. its a 36x18' shop with two rooms.

i'm moving the AC unit over by the exhaust and cutting another hole in the shop for fresh air intake which will go to the intake on the AC then the exhaust will be exhausted out of the shop so it will be completely sealed now.

i'll get some pics when i get done.
 
whatapothead

whatapothead

Well-Known Member
so 6" none insulated duct that will be about 8' long and then 6" Insulated duct that is about 10' long with a 400cfm fan blowing out.
 
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