As we approach Halloween, I thought it would be appropriate to answer a question about certain strange sounds in the home. “Steve, every night when I lay in bed I hear knocking and when the furnace turns on there is a tack tack sound for a little while. Haunted house maybe?” I don’t know if the house is haunted; but I do have some ideas about what that sound might be.
When your furnace turns on, the metal duct work in your home is cool. As the hot air rushes past, the metal heats up causing it to expand. As it expands, the metal can’t move at first since it is held in place by nails and friction. The metal keeps expanding until it overcomes the friction from the wood and drywall and it slips, causing that sound. It is pretty normal to hear a few sounds quickly together when your furnace turns on. When the furnace turns off, the metal cools slower. You will still get the same sounds but there is more time in between them. The same idea applies to your whole home. For example, now in the Fall, the entire home is warmer during the day causing the WHOLE house to expand slightly. At night, as it cools, the house contracts. Different materials contract at different rates. So, as you lay in bed…while everything is quiet…you can often hear the home shifting and its not usually something supernatural.
Happy Halloween Everyone!
If you would like to read about the clanking sound when turning off the water known as water hammer; I will be posting that in Mid October…
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