solar hot water panals on your roof would get your water even hotter and collect that heat befor it got to your attic, they also have the possiblity of heating enough water that after your domestic hot water is hot, the extra heat can be used to heat your living space, or hot tub, or whatever.
drawing hot air from your attic for yoru drier sounds like a good idea if your drier has a thermostat that is sensitive enough to prevent it from over heating, and I hope that it would, but if it doesn't then you are just getting your drier that much hotter/closer to starting on fire, so I would start out by calling a repair center and ask them if this is a fire danger, then get a good air filter to prevent dust build up on the heating eliment.
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