I have a 3 story townhouse, the bottom level is extremely cold, the second level is moderately cold and the top level is warm and toasty. Actually top level gets too hot in winter as the thermostat is constantly being triggered by the colder downstairs. This townhouse is also an end unit so it takes the brunt of the cold. I recently realized that there is no insulation in the walls! I am planning on cutting square shaped holes in the drywall, between each stud, near the ceiling and blowing in the insulation, then patching them up.
My question is that since the top level is already warm enough, can I put insulation in the bottom levels only? Will it still work to provide a warmer environment downstairs, even though third story walls are not insulated?