It was worse during the winter. The room last on the heat run, and the sound seems to come from the front of the room, where there are two windows over a large hot-water radiator. I¹ve heard a snapping sound as I enter the room and move to those windows. Any ideas?
A. Sounds like a Stephen King novel. The possessed radiator and the accomplice window are plotting to chase you from your house. Actually, you have a solvable problem caused by expansion and contraction. Radiator heat causes wood wall parts and windows to move. The movement comes in a few different forms. You have thermal expansion, which rubs wood against wood, and along the nails holding the wood. This slight movement causes a popping sound. If the wood has moisture in it, as a result of the heat inside meeting the cold outside, expansion is more extreme.
Windows also experience changes. If they¹re made of wood and vinyl, the two materials move at different rates. As they expand past each other, it¹s like a bow rubbing the strings of a violin. The result is a small popping sound. Any of these could be the source of the sound, which could be caused by the lack of separation between the radiator, the walls and windows. The walls may be poorly insulated, as is typical in older homes. Often the only thing between the radiator and the outside wall surface is fiber board and reflective backing. Homes used to be colder, because boilers pumped out heat that escaped through poorly insulated walls. Fuel was cheaper, boilers were bigger and took longer to distribute the heat.
The end of the heat distribution line should actually be a little cooler than the rest of the run, but if the insulation is poor, expansion and contraction still occur. Two other possibilities also have to do with heat, cooling and movement due to the wind or the time of day. Your home is like a big balloon. As the sun heats your home during the day, the whole house actually expands a little. It also rises up a fraction of an inch out of the much cooler ground. This causes the materials in the walls, the windows, the siding‹ everything ‹ to expand. As the house settles at night, the contraction again causes popping sounds.
The internal stretching of the materials will also cause the sound, as does the wind pushing against the walls, like the sail on a boat. One side pushes in and the opposite side pushes out. In winter, wind mostly comes from the northeast, and the opposite side is the southwest. The next time you hear the sound, note the wind conditions, the outside temperature, whether the insulation is adequate ... and one last thing: Are the heat pipes fastened directly to a hard surface, or are there resilient spacers? Pipes fastened to a hard surface expand and contract, and so will also create the sound. Water hitting the end of the run will also create a slight banging sound. Any of these conditions could be the source of your problem. Good luck!
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