Thanks...I did try to power the SSR directly from the Arduino in the past but it wasn't enough power, so I used a MOSFET and that worked. But, I was powering the Arduino only from my computer's USB port, and I've read that less than 6v may not be enough to get full power from the pins...am I right about this?
The heater is 1200 watts so I don't know if it would be too much for the MOSFET. The fan is the problem for me -- today it was spinning too slowly, and I was only getting 2.3v to the MOSFET and 8v to the fan (using a 21v power supply). Perhaps this is also a result of using USB power to the Arduino?