no... it's not a solid wall. I had planned to have an angled grate to let the fan blow through, yet still block out light which may come from wherever (gonna be in a basement, so not much). i am trying to do this without the use of exhaust fans and such, 'cause I'm gonna be renting. No use gettin too elaborate until I'm gonna stay put. I figured between the fan and open top, heat would be taken care of, but I may need to figure something else out to deal with the light issue. Playing with the idea of getting rid of the aquariums and using soil with nutrient/CO2 lines... which tends to be more productive?