What can be the most different temperature levels in the basement & 3rd floor, while the thermostate set to 21C degrees

what can be the most different temperature levels in the basement & 3rd floor, while the thermostate set to 21C degrees


Unless regulated by local code it can be any temperature. I suggest you contact your local building department to see if there codes/regulations cover this. I would also like to mention that unless the code specifically addresses this issue the basement does not have to be heated since it is not considered a living space. Now if it has been converted to a living space by obtaining a permit then it will be covered by whatever the code says.