Tests indicate that the shirt board will increase to about 140 degrees F after an hour of typical use.
This is a benefit as it will decrease your flash time.
However, take this increase into account when flashing by checking the ink for tackiness on a regular basis. Adjust the heater away from the shirt board if you notice the garment is getting too hot too quick.
Also consider the Flash-A-Matic, an automatic device to swing the heater away from the shirt board after a time delay. This will reduce the guesswork of the flash time and avoid unnecessary heat being applied.