Make sure you get a thermostat with the heater. None of the pet stores in my area carry thermostats some do have rheostats. You really need be able to control the heat source. Get an acurite indoor outdoor thermometer from wall-mart. With this you can place the probe over the uth to get a temp reading. The indoor temp will measure your ambient temperature and your humidity. I do not know if Douglas fir is bad or not, I just know I have used aspen in all my cages with success. Safe for the snake, holds humidity, and snakes that like to borrow will tunnel through it and make tunnels.