Ask the Architect

What’s with the popping?

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Q. My southwestern bedroom on the first floor of a 1951 cape goes snap, crackle, and pop — a lot. It’s worst during the winter. This room is the last on the heat run, and the sound seems to be across the front of the room, where there are two windows over a large hot-water heat radiator. I’ve heard a snapping sound as I enter the room moving 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. You must resist the force. 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: thermal expansion of the wood, 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 from inside meeting the cold from outside, wood expansion is more extreme. As they expand past each other, they play like a bow rubbing the strings of a violin. The result is a small popping sound.

Any number of sources, or even lack of separation between the radiator and the wall, can cause it. The walls may be poorly insulated, typical in older homes. Often, the only thing between the radiator and outside wall surface was fiber board with a reflective backing. Homes were colder, people wore sweaters, and drafty homes had more fresh air. A warmer home was in the high 60s, because boilers pumped out more heat that escaped through poorly insulated walls. Fuel was cheaper, boilers were bigger and took longer to distribute the heat.

Two other reasons relate to sun, heat, cooling, wind or the time of day. Your home is like a big balloon. As the sun heats it during the day, the whole house actually expands a little. It also rises up out of the much cooler ground a quarter- to a half-inch. This causes the materials within walls, windows and siding to expand. As the house settles at night, house contraction, again, causes popping sounds. The internal strain of materials will also cause popping, as does the force of wind pushing against exterior walls, like the sail on a boat. One side pushes in, the opposite side pushes out.

The next time you hear the sound, take note of wind conditions, outside temperature and whether the insulation is adequate. And one last thing: If they’re visible, are the heat pipes fastened directly to a hard surface, or are there resilient spacers? Heat pipes fastened to hard surfaces expand and contract, creating the popping 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. Let us know what you discover. Good luck!

© 2016 Monte Leeper. Readers are encouraged to send questions to yourhousedr@aol.com, with “Herald question” in the subject line, or to Herald Homes, 2 Endo Blvd., Garden City, NY 11530, Attn: Monte Leeper, architect.