My house in southern Ontario, Canada, has a cold cellar under the front porch. The house also has a sump pump, located in the cold cellar.
The builder insulated the perimeter basement walls, including the wall separating the cold cellar from the main area of the basement, leaving the porch un-insulated and outside the warm air envelope of the house, and included two 4" vents in the cold cellar.
The original/previous owner insulated the exterior walls (down to the floor) and ceiling of the cellar and blocked up the vents, effectively making the cellar part of the warm air envelope of the house. Part of the problem of doing this is the humidity and odor introduced into the "cellar" space by the sump.
I have chosen to re-open one of the vents, and keep the (insulated) cellar door closed. The concern I have is temperature inside the cellar because of the sump (don't want it to freeze). With outside temperatures having briefly dipped to -15C, I found the cellar temperature drop to about 4C.
Can I expect the cellar and sump to remain above freezing throughout what could be a colder than average winter (can expect periods below -25C)? Will the insulated walls prevent the cellar from drawing enough ground heat to stay above freezing? In other words, should I pull off the insulation below the frost line (about 4ft below grade)?