Why one apartment is cold while the neighbor's is hot

It’s not random. Uneven heat distribution is a typical problem with old heating systems, and there’s an explanation for it.

Cause 1. The system isn’t balanced. Heat carrier fluid flows along the path of least resistance. Apartments closer to the heat substation get more, the farther ones get less.

Cause 2. Air in the radiators. A cold bottom or top on a radiator usually means there’s air trapped in the system.

Cause 3. A rebuilt system inside an apartment. Radiators swapped for a different capacity, or underfloor heating added, changes the flow through the whole riser.

Cause 4. The apartment’s location. Corner apartments, and those on the first and top floors, lose more heat.

Cause 5. Covered radiators. Curtains, furniture, and decorative panels cut heat output significantly.

The fix. Start with bleeding the system and hydraulic balancing. That’s a building-level job, and it’s what makes the biggest difference.