How warm you thinking? Warm the air via the green house, keep the fish outside. Use fast moving shallow water, and it will help cool the water too. Slow it down, and it heats up.
Honestly though, the trout I have kept are happy to about 60 degrees, sometimes a little higher....but the cooler the better. Even here in TX a lot of people farm them in the winter as a winter crop. They can't handle the heat.