This is not a very good idea for several reasons. The greatest problem that you will encounter is excessive moisture. When you put clothes in the dryer, they are wet. In the drying process, the water in the clothes ends up exiting through the vent system. I guarantee that your tools will rust and you will have problems with condensation everywhere inside the garage. The only way that you could provide heat from the dryer without the moisture is to run the dryer without any clothing inside. As you know, running a dryer requires a good amount of electricity and it would not be very economical. To add to that, if your garage is detached from the house, most of the heat will be lost where the vent runs outside between the house and the garage.