Stop Annoying Sounds from Plumbing and Furnace

By James Dulley

November 30, 2017 4 min read

Dear James: I have lived in a new house for about one year now. Whenever I use a lot of hot water or the furnace/air conditioner comes on, I hear squeak and knocking sounds. What is it and how can I stop it? — Mona S.

Dear Mona: Those sounds you described can be quite loud and a little scary for children. I can still recall spending the night at my grandparents when I was a child. Their plumbing and heating system made many strange frightening noises which kept me awake and anxious all night.

Most of knocking sounds you are hearing are from the water pipes expanding and contracting as hot water runs though them. First they heat up and expand and then they cool down again when you turn the hot water off. The sounds are usually louder when you turn the water on because they heat up much faster than they cool back down.

The copper supply pipes expand some, but not as much as the plastic (PVC) drain pipes. Plastic expands much more with temperature increases than metal does. Most new houses use PVC pipe today, so you can expect to always have a few sounds, but not at the annoying level.

For those of you who are planning to build a new house, consider installing cast iron drain pipes instead of plastic. It is more expensive, but it will virtually eliminate these sounds. Cast iron pipe also reduces the sound of the water running through the pipes. This can be a great advantage particularly for second-floor bathrooms.

Another source of the noise is caused by the pipes rubbing against floor and wall joists as the expand and contract. If the builder was not careful to support the plumbing properly or saw large enough clearance holes for it, you will hear a squeak or a ticking sound as the pipe rubs against the wood.

There really is no simple fix for this problem. The best you can do is try to locate the spots where the sound seems to be the loudest and most annoying. Remove a section of the drywall to gain access to the suspect pipe. Support it better so it does not touch the lumber framing.

Making the holes in the lumber a little large will provide more clearance around the pipe and may stop the rubbing. Be careful not to enlarge the clearance holes too much because it weakens the joist or stud. Check with your local building inspections department for the maximum allowable hole sizes.

The sound when the furnace starts is somewhat similar to the pipes. The ducts will grow and shrink as they warm up. Support them properly so they don't rest against the lumber. Also, secure all the duct joints because this is a location where one piece will slide against another - squeak!

A loud knock, when the furnace starts and stops may be the sides of the large main ducts buckling in and out. This is sometimes called "oil canning". The increasing and decreasing air pressure inside the ducts causes this to happen usually in the large flat ducts near the furnace.

Screw some long heavier sheet metal supports along the duct faces that are oil canning. Sometimes, just putting small dimples in the face with a hammer will make it rigid enough to stop the noise.

Send your questions to Here's How, 6906 Royalgreen Dr., Cincinnati, OH 45244 or visit To find out more about James Dulley and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at

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