Does my 250w HPS stealth cab need cooltube or a bigger exhaust fan?

I built a stealth cab (6ft/3ft/2ft):
x 250w HPS Lumatek Dig. Ballast
x 4 inch carbon filter
x 4 inch exhaust fan (180 m3/hr)
x 1 PC fan for ventilation
x intake opening twice as bis as the opening for the outtake

Im planning to use the HPS for vegging and flowering. While the temperature in the cab is around 70F when its dark, it goes up to 88F when light and ventilation is hooked up. Humidity decreases from 50% to 30%. From what I understand, this is anything but ideal.
Up to this point I already spent more than Ive originally planned but now I came this far so I have to fix this.

1. Questions is, will a cooltube help drop the temperature or do I need a bigger and stronger exhaust fan? Please dont tell me I need both! lol

2. Question... If I need a cooltube, there wont be enough space with this current set up. I guess I have to mount my exhaust upside down, right under the opening. Thats connected to the cooltube which is in the middle and the other end connected to the carbon filter. I dont wanna place it on top of the cab cuz of the noise. Im studying the structure of the fan, how the fck can I mount this upside down? Any tips?

Thanks a lot for your help

I'd highly recommend making a DIY cool tube. I also had major heat problems in my 2' x 4' closet grow until I went with the cool tube. Now I'm running a double cool tube (two 250w) and my tempuratures average in the low to mid 70s. A bake-a-round and some 4" PVC drain pipe fittings makes a simple and sturdy cool tube. I attached some pics of my double cool tube.

You can make a single by buying two 4" PVC drain pipe fittings (either straight or elbow according to your needs). Use a two-layer wrap of that foam and foil pipe insulation wrap around the glass to get a snug fit in the fittings. Then use standard dryer-vent couplings to connect your ventilation ducting.

GreenGrin said:

I'd highly recommend making a DIY cool tube. I also had major heat problems in my 2' x 4' closet grow until I went with the cool tube. Now I'm running a double cool tube (two 250w) and my tempuratures average in the low to mid 70s. A bake-a-round and some 4" PVC drain pipe fittings makes a simple and sturdy cool tube. I attached some pics of my double cool tube.

You can make a single by buying two 4" PVC drain pipe fittings (either straight or elbow according to your needs). Use a two-layer wrap of that foam and foil pipe insulation wrap around the glass to get a snug fit in the fittings. Then use standard dryer-vent couplings to connect your ventilation ducting.

View attachment 1516679View attachment 1516681View attachment 1516682View attachment 1516683View attachment 1516680

Click to expand...

Thanks man appreciate the pix and tip. But I dont have much time to build this DIY cooltube due to work and all , plus Im no handy mandy anyway. I might go with a cooltube from the grow shop.
Just before I get one, Im trying to make sure that it thats what is missing and not a stronger exhaust fan... So one point for cooltube.