Question: We have an e-series heatilator fireplace and I love to have large roaring fires. Is there any limit (other than the size of the box!!) to how hot I should allow the fire to be? Will this affect the longevity of my fireplace? We have some hairline cracks in the refractory coating, the heatilator web site says not to worry until they are 1/8th of an inch in size. Does this sound reasonable? Answer: Yes, the cracks are nothing to worry about. There are metal walls behind the firebrick panels which are the actual firewalls of the unit. You can run the fireplace hot once in a while....but don't burn trash or construction lumber. Also, be sure to keep the fireplace doors open when running a hotter fire. Lastly, make certain that the fireplace glass doors (if any) that you have are the factory recommended ones....NOT generic doors, which should not be used on pre-fabs.