You can do the dry ice thing... but, IMO, it's really impractical.
I think you need to see it for yourself...
I like that you're "thinking outside the box", but, again, just my opinion, it's impractical.
But hey, try it if you want!

Temperatures:::
1- good fans.. you can have good airflow in there. That will help.
Nothing beats an air conditioning unit... but it's completely do-able without!

2- cool tube... these help tons. And are easy to build your own.
You can check the FAQs for build your own... and/or eBay for "Bake-A-Round"



Best,

-turtle420
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turtle420 Reviewed by turtle420 on . Changing Bulb I am looking to do a smaller grow, build a more concealed cabinet. I currently have a 400W hps and want to down grade to a 150W or 250W since I only have 3 plants and pretty small area about 3ftx1.5ftx4.5ft. Can I use the same ballast reflector (the 400W) for a smaller bulb? Will using a smaller bulb help with heat? Thanks for any help. Rating: 5