That co2 thing I am going to run a grow outside as soon as I can figgure out how to put up this 'easy' to build greenhouse kit I just got. I'm thinking of running the venting from my pump shed into it. I have a gas heater for the pool in it, and the building has tons of vents in it so I don't think it CO2 levels can get over the max. Water heater sounds cool. That head isn't just a hat rack huh?