Id have to cheat and count wind chill to make a 100 deg delta. It was -8 ambient, -30 with wind chill and 70 inside. So a true 78 deg delta. Ill take it but hope I dont have to do it again. It was too cold in one section of the house and the cold water pipe froze but luckily didnt burst. I kept the warm water running hoping it would keep enough heat behind the wall to keep the cold water from freezing. It didnt work. next time Ill let the both run if it gets this cold. The worst part was our bedroom was too warm. The guy that designed our cabin put way too many registers in the master bedroom. We have 8 and with all of them closed it was still 70 degrees. I sleep much better around 60 much to my wifes dismay. The Kuma does amazing on a load of osage/locust. Its incredible how much heat it is still putting off when you wake up in the morn.