Apartment 6A should be the same temperature as apartment 6J during the winter. As most apartment building owners, co-ops, and condos know, this is rarely the case. The reality is that apartment 6A could be 80 degrees(overheated) and apartment 6J could be 65 degrees(under-heated). The fact that one apartment is too hot means that the building is using far more heating fuel than is necessary. The fact that the other apartment is too cold means that the heat is not effectively getting to certain apartments. It is the number one cause of excessive heating fuel costs. Further, it is a situation often made worse as the building attempts to provide even more heat to the building in an effort to satisfy the low temperature apartments.
Fortunately, this can be resolved and buildings can significantly reduce their heating oil and/or natural gas costs. Every temperature degree reduced is equivalent to a 3-5% heating fuel reduction. Imagine being able to heat all the apartments to a comfortable 72 or 73 degrees instead of heating some apartments to temperatures of 80 degrees and higher. Imagine the energy savings.