Kevin, I'm redoing my in-wall setup in the upcoming weeks. Your's will be 3X as big as my 120, but a lot of the concepts are the same. Here's some ideas based on the mistakes I made on my fishroom.
- Heat buildup will be a problem in that room. Plumb your chiller and locate any other hot items like MH ballasts outside of the the room. It'll put less stress on the cooling unit and your chiller since your aquarium won't be absorbing the ambient heat generated in the fishroom.
- A mini-split ac unit would be a good idea if you can afford it. They're way more efficient than a standard window unit and help with the electric bill during the summer months.
- Be careful with an exhaust vent. Where's the fresh air going to coming from? If you're pulling air from the garage or outside of the house, you're going to have problems during the hottest part of the year, since the air your removing is being replaced with 90F+ from the garage or outside. Whatever you do, do not pull air from inside your house. You'll thank me when you avoid a sky high elect bill because your house HVAC is working to overcome heat coming in from outside or from your attic.
- a cooling unit will help de-humidify the room since water will be condensing on the evap coils. A stand alone dehumidifier would probably be a better idea than an exhaust fan.
- Use green board on every wall in the fishroom and seal the baseboard to prevent water damage from any leaks, 'cause we all know it's bound to happen at some time or another.
- Stick with the concrete instead of tile. You can always seal the concrete with swimming pool paint.
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