Portable AC, Bad Negative Pressure

Hey guys. I'm hoping someone with experience in this can help me.. I have a 12x20x8 ft grow room (1920 cu ft), very well insulated. It was actually getting too hot in the winter even lol. For this summer I installed a Whynter ARC-14SH dual-hose portable ac unit (14,000 BTUs). Everything seemed fine for the first couple weeks but then I noticed it was creating BAD negative pressure in my room. If you go outside, you can physically feel that the exhaust hose is blowing out twice as much air as the intake hose can take in, if not more. And the exhaust sometimes gets so hot, it can almost burn you. I am afraid of this unit overheating and catching fire. It cannot keep my room under 85 when it's 90 degrees outside. This is actually just a Statesman shed I had installed from Lowes, and then I drywalled and outfitted to my liking. I have vinyl flooring over the plywood, which I did not glue down. The negative pressure is so strong that it is sucking air through the floor, raising the vinyl like a parachute. It's stretching the vinyl and warping it. Some spots I even noticed some raised nails that weren't there before. So the pressure is obviously strong.

Do you think this AC unit is incapable of keeping my space cool? I think the problem is all on the exhaust.. it's blowing out the grow room air. I read that the exhaust should never be more than 10-20% stronger than the intake fan. And if negative pressure wasn't an issue.. The grow room air exhausting is because I plan on running a CO2 burner to boost the plants. They claim dual hose systems are not supposed to created negative pressure, no inside air should be escaping. Should I say screw it and install a window AC instead? I'll just cut a hole in the wall. That's how my portable is installed. But I am very upset since I paid $570 for this thing, just to be set up for a fail. I also feel it's dangerous being in the room. I get very lightheaded after about a half hour, and I think it is because the AC is exhausting all of the available oxygen. I'm against installing a passive air intake. I want this place sealed down!

Please, if anyone could help it would be greatly appreciated I'm hoping to finish this today and get my 12-site Ebb&Flow going. I have a bunch of Heavenly Scout clones that need to be transplanted asap.

jsisko01 said:

Hey guys. I'm hoping someone with experience in this can help me.. I have a 12x20x8 ft grow room (1920 cu ft), very well insulated. It was actually getting too hot in the winter even lol. For this summer I installed a Whynter ARC-14SH dual-hose portable ac unit (14,000 BTUs). Everything seemed fine for the first couple weeks but then I noticed it was creating BAD negative pressure in my room. If you go outside, you can physically feel that the exhaust hose is blowing out twice as much air as the intake hose can take in, if not more. And the exhaust sometimes gets so hot, it can almost burn you. I am afraid of this unit overheating and catching fire. It cannot keep my room under 85 when it's 90 degrees outside. This is actually just a Statesman shed I had installed from Lowes, and then I drywalled and outfitted to my liking. I have vinyl flooring over the plywood, which I did not glue down. The negative pressure is so strong that it is sucking air through the floor, raising the vinyl like a parachute. It's stretching the vinyl and warping it. Some spots I even noticed some raised nails that weren't there before. So the pressure is obviously strong.

Do you think this AC unit is incapable of keeping my space cool? I think the problem is all on the exhaust.. it's blowing out the grow room air. I read that the exhaust should never be more than 10-20% stronger than the intake fan. And if negative pressure wasn't an issue.. The grow room air exhausting is because I plan on running a CO2 burner to boost the plants. They claim dual hose systems are not supposed to created negative pressure, no inside air should be escaping. Should I say screw it and install a window AC instead? I'll just cut a hole in the wall. That's how my portable is installed. But I am very upset since I paid $570 for this thing, just to be set up for a fail. I also feel it's dangerous being in the room. I get very lightheaded after about a half hour, and I think it is because the AC is exhausting all of the available oxygen. I'm against installing a passive air intake. I want this place sealed down!

Please, if anyone could help it would be greatly appreciated I'm hoping to finish this today and get my 12-site Ebb&Flow going. I have a bunch of Heavenly Scout clones that need to be transplanted asap.

Click to expand...

can u install a window shaker unit instead of the portable

your going to need to go go to a active intake .......build yourself a filter box

or your going to need to make a passive intake something like 16x16 from the sound of it

justugh said:

can u install a window shaker unit instead of the portable

your going to need to go go to a active intake .......build yourself a filter box

or your going to need to make a passive intake something like 16x16 from the sound of it

Click to expand...

I can install a window ac, I'm just upset I wasted that money. If I cut a passive intake, won't it just make things worse? The ac unit is already fighting hard to keep it cool in there, and then that open airflow will just warm the place up right?

What if I installed a 400 CFM fan to the intake, to boost the intake flow and equalize the pressure? My only concern with this would be getting the fan to run at the same time the ac unit turns on. And also the possibility of creating positive pressure inside the actual ac unit.

What do you think? I'm just trying to make this portable work before I go cutting new holes in the wall. There will be no going back after that.

jsisko01 said:

I can install a window ac, I'm just upset I wasted that money. If I cut a passive intake, won't it just make things worse? The ac unit is already fighting hard to keep it cool in there, and then that open airflow will just warm the place up right?

What if I installed a 400 CFM fan to the intake, to boost the intake flow and equalize the pressure? My only concern with this would be getting the fan to run at the same time the ac unit turns on. And also the possibility of creating positive pressure inside the actual ac unit.

What do you think? I'm just trying to make this portable work before I go cutting new holes in the wall. There will be no going back after that.

Click to expand...

well a window AC will fix the trouble .......it is the exhaust of the portable AC and the air in the grow room

1 window ac (it is almost sealed 85% or so) ....it cycles the air in the room with out causing the suction like u are talking about

2 a active intake ...........the active intake will always be running (u can tweak the numbers with a speed controller to maintain negative)
A what is the intake system now
B what is the exhaust fan rated
C what CFM listed for the ac .......dual exhaust is it moving alot of air (is it 4 inch or 6 inch ducting)

3 move off a exchange system to a C02 system u supply ........with your sealing and all that this might be the best choice for u ......but it does cost a room your size needs a burner
A burner
B controller with a light senor

these types are nice. i use one in the studio. it has swivel wheels and attatches to the window via a hose and adjustable ABS plastic panel that fits under a propped open window. $100-$300 new depending on size. cools a 110°F room down to 68°F no prob.


https://www.groupon.com/deals/gg-lg-air-conditioners-manufacturer-refurbished?deal_option=c10a5dc4-188a-11e6-a446-00259060b5da&utm_source=Google&utm_medium=cpc&utm_campaign=US_DT_SEA_GGL_TIM_TTT_PADS_CBP_CHP_NBR_g*gg-lg-air-conditioners-manufacturer-refurbished_c*103296035341_k*_m*_d*Goods-Product-Ads_mobile*true_keyword*_target*_adposition*1o6_prodtarget*60110792186_adtype*pla_merchantid*10018412_productid*46264347_productpartitionid*60110792186_campaignid*600843543_adgroupid*27871071541&mr:referralID=bba39f7e-422e-11e6-bdfa-005056946dac&gclid=CjwKEAjwkui7BRCf64DNtfDupgoSJAA_0LOohjvRs25a46LtAMxMxl9B-L2GfZ1Dpho2BU5mLb8PhhoC_Mzw_wcB&fallback=true&bypass=true

nxsov180db said:

Whatever your getting lightheaded from it's not the lack of air/O2 from negative pressure I can promise you that, the amount of negative pressure you would need to not have an adequate amount of air to breath would be far more than a little fan inside an a/c can produce... Anyways on to the fix, Yes if you can install a window a/c then do it. No even dual hose portable's still exhaust room air unless modified check this out https://www.rollitup.org/t/modifying-portable-a-c-for-use-in-sealed-grow-room-w-co2-tutorial-w-pix.887831/#post-12008986

Click to expand...

Thank you! That article is a great find. I think I may try that instead of buying a window shaker. I just got back from Lowes and the 15,000 BTU units and above are huge. I would have to build some type of wooden support outside the shed for it. Sealing my dual-hose AC unit will be a lot less time consuming, easier, AND cheaper I'm a little concerned on how safe this may be though.. the guy seems like he's very experience but I wonder if doing this could be a fire hazard? Maybe I'll PM him. Do you think I could continue using the 4 inch hoses that came with the unit? Instead of expanding to a 6 inch ducting like he did. If it's not necessary, I would like to avoid cutting the holes in my wall larger, because I like how I have the set up outside already. I know I'm being lazy lol. But I was thinking just attach fans to the back of both the exhaust and intake, and then use a ducting reducer to connect the fans to the 4" hoses. I think that would be adequate since I won't be using such powerful fans anyway?

Also, I installed the AC unit in the corner of my room. But I basically have a whirlwind of circulation in the room. So that shouldn't be a problem right? A fan in each corner plus my 1709 CFM Phat Fan which I use to scrub and circulate air in the room, and exhausts on a Y-split for better circulation. It grabs the cold air from the AC and the CO2 burner hanging from the ceiling. Here are a few pics of my set up for you guys. Some of the pics are old, from when I had a grow that I lost (the files are dated actually). And please excuse the mess lol


This is what I'm running:

6 - PGX5-600 (600w) LED lights by HydroponicsHut
7 - Galaxyhydro (300w) Dimmable Full Spectrum LEDs (Supplement lighting)
Link4 Corporation LC99511 iPonic 614 Environmental Controller
Whynter (ARC-14SH) 14,000 BTU Dual Hose Portable AC with Heater
DeLonghi EW7707CM Portable Oil-Filled Radiator
Gotham Hydroponics Liquid Propane 8-Burner
SPT SD-72PE Dehumidifier (70 pint)
12" Phat Fan, 1709 CFM
Phat Filter 39"x12", 1700 CFM
12" Phat Muffler (This thing really works!)
Oxygen Pot Systems 12-Site Ebb&Flow
4 - Hydrofarm AAPA110L 110-LPM Active Aqua Air Pump (When I do DWC)


I just moved the AC unit at an angle today to extend the exhaust hose as far as possible, while keeping the intake hose as short as possible. This seems to balance the pressure a little better, but probably makes it run hotter too..? Gonna try sealing it up tomorrow and show you guys.

nxsov180db said:

Well "the guy" is me lol but yes as long as you are keeping the distance no longer than the factory 4" hoses allow then continuing to use them would be fine. Yes the circulation fans you have now are fine they aren't going to hurt anything that's for sure. No need to worry about a fire hazard just let the a/c sit upright 24 hours before turning it back on after you take it apart and seal everything up...

Click to expand...

Haha wow I feel smart. Didn't realize it was you.. So yeah I have the Whynter ARC-14SH so I'm assuming the body inside my unit should almost be identical to your tutorial I'm hoping? I am going to try and get a hold of Whynter customer service one last time, they keep being dodgy and only replying to my emails once a week. They're claiming my unit is too big for the room it's in lol.. But I would like to see if they're going to do an exchange with me before I crack this thing open. And then I'll modify the new one I get. I would feel more at ease if they send me a replacement unit because I still have a bad feeling this unit isn't running the way it should. It was much more efficient during the first month of use

You need something like this. That one is 220vac. It's just a quick example. It only has small tubes with coolant instead of 4" ducting so no air gets blown outside. Just look for "split" and "inverter" in the name.

nxsov180db said:

Whatever your getting lightheaded from it's not the lack of air/O2 from negative pressure I can promise you that, the amount of negative pressure you would need to not have an adequate amount of air to breath would be far more than a little fan inside an a/c can produce... Anyways on to the fix, Yes if you can install a window a/c then do it. No even dual hose portable's still exhaust room air unless modified check this out https://www.rollitup.org/t/modifying-portable-a-c-for-use-in-sealed-grow-room-w-co2-tutorial-w-pix.887831/#post-12008986

Click to expand...

Very nice, I hope the OP reads it.

Can you tell me if this is bad? It looks like these coils are leaking coolant maybe?

You're probably going to kill that AC unit based on what you're experiencing. I used to burn one up every summer, after 3 of them i went to a mini split. I ran my exhaust through a 6" phresh filter for smell reasons, and the extra load was too much. 3-4 months and each unit was toast. If you're mad now, you don't want to look at your electric bill when it comes after running that portable AC for a month! they are very inefficient!

So I've been in the process of sealing this unit inside. Today I picked up the AC unit and didn't realize my arm bent this copper pipe. It's very small and feeds off of the larger pipe. Like just 4 inches sticking put in the air. Now that I've bent it, I'm sure it will block the flow of anything passing through. It literally bent down in half. I'm assuming this little thing is to relieve pressure? I hope I'm not screwed now. Here's some pics

Okay thanks. The job is finished but I am going to let it dry out for a few days.. the sealant I used is some harsh/deadly stuff lol. DAP seal N peel. It's clear and the chemical fumes are so strong.

I will be posting pictures of the steps I took in doing this, and I'll give credit with a link to your thread since I learned how to do this from you.

And the copper wasn't cracked but it's very thin and I was surprised how easily it bent. I am a little nervous that it could rupture one day now that it has a weak point in the bend. I could snap it off with ease if I just bent the opposite way, so hopefully the pressure will hold... especially a year down the road from now, if not longer.

Think your ok looks to be on the low side.
Not a clear pic from my vantage point. Use to do Hvac.
The one i had pulled almost 12amps 2 motors or a double shaft and a pump.
And It did not due as good a job as the damn ole reliable Window A/C.

jsisko01 said:

. It cannot keep my room under 85 when it's 90 degrees outside.

Click to expand...

Useless....if the head pressure gets to high,so does suction.Which raises the evap coil temp. Rule of thumb we used 500 sqft per ton on a well insulated structure.
Take the temp of Supply and return then subtract.That will tell you the problem

Thank you all for your reply. I already sealed the unit up so let's hope the bent pipe is okay lol. My AC also pulls 12 amps and it's having a hard time keeping my room under 90 on a hot day.. BUT the negative pressure issue is completely solved

nxsov180db said:

How many tubes of that stuff did you have to use? I can't wait to hear how well it works!

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I used like 5 tubes haha, but I also wasted a lot. I was globbing it on then scraping the excess off and throwing it away. That stuff was like $6 a tube. I couldn't find the stuff you used, it looked like foam? My local Lowes has shit for variety. But this stuff worked great other than the smell. It was so harsh on the lungs and took days for the vapors to be gone. But the unit runs great, no negative pressure whatsoever and I haven't even taped the seams of the shell yet like you did. I attached a few pics. I used a water supply line for my drain hose so I have flexibility and length. I may run it through the wall to drain outside because it really pulls water fast. I still can't use this unit until I buy a stronger fan. I added a 240CFM to the intake as a test but it definitely needs more air. The exhaust is blowing so hot it could almost singe your hairs. But I'm assuming it would shut down if it reaches a dangerous level? Unless the temperature gauge that reads the heat is sealed at the top now? But I doubt it. I didn't seal the hoses to the back yet since I'll be upgrading. I just have the fan leaning against my radiator right now lol. I sealed the back of the unit a little differently as well since the caulk I used was too liquidy. I cut some sheet metal, placed it standing up right, and then squirterd caulk down into the drilled holes. Without the sheet metal, the caulk was just leaking down into the water drain. But thank you so much for discovering this tweak. I'll be making a tutorial thread of my experience soon.

How did it all turn out a couple years later? I have a similar AC and i'm not sure what to do yet. Negative pressure like crazy in my tent pulling out all of my co2. I already spent so much money for the AC... why isn't there one out there that just circulates the air inside of the room. Like a mini split

thirdeye420 said:

How did it all turn out a couple years later? I have a similar AC and i'm not sure what to do yet. Negative pressure like crazy in my tent pulling out all of my co2. I already spent so much money for the AC... why isn't there one out there that just circulates the air inside of the room. Like a mini split

Click to expand...

I would suggest to not even do these mods honestly. It's a fire hazard. Yes it did fix the negative pressure but by me rerouting the water drainage, the unit was overheating. The condensation collected drips down into the unit as an added cooling mechanism. You could actually still perform these mods and just leave the water how it is, you shouldn't lose too much CO2 from that small hole.

But I would honestly suggest buying a window unit. I cut a hole in the wall and hard mounted it. It fixed the negative pressure issue AND runs way better and cooler. Those portable AC's just don't have the power. I have a 14,000 BTU window unit that blows the portable one away.

Great thread!