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Ask the Carpenter: Sound-reduction tips for your plumbing

Ask the Expert Home Improvement
Adding standard fiberglass, acoustic, or recycled cotton insulation would help reduce the noise from this water heater.
Adding standard fiberglass, acoustic, or recycled cotton insulation would help reduce the noise from this water heater. HANDOUT

Q. I live in an 1800s home with a shallow basement, and our water heater started leaking. I frantically called around and found a plumber, but he refused to replace it because the power vent had a flexible hose. (The plumber said it wasn’t up to code.) I hired another plumber, who said he would replace it, but only if he could cut a new hole for a rigid vent pipe. I agreed. He drilled a hole in an old beam (is that safe?), and there is now a new PVC pipe leading outside. (See photo.) The old flexible hose bent down to a hole in the stone foundation, and it was quiet. This new one is loud. The floor vibrates. Our bedroom is on the second floor above the kitchen, and I can hear a hum as it starts up when I’m in bed. When I called the plumber about it, he just said, “Throw some insulation above it’’ and got off the phone quickly. Is there anything I can do about the noise and vibration?

RR, Cambridge

A. Cutting the existing hole with a hole saw is almost impossible to do — a new hole makes sense. Hire a carpenter to patch the exterior of the house and insulate the interior rim joist. Putting insulation above it may also help. Try Rockwool acoustic stone wool; it’s a sound-dampening material.

The first step in noise control is accurately diagnosing the source. Many times the best course is to reduce the noise as close to the source as possible. This is often the case when you’re dealing with loud air-conditioning compressors, fans, or other HVAC equipment.

Consider reverberation reduction. Reverberation is the echo that sound creates as it bounces off surfaces in a room rather than being absorbed. This often means the installation of double- or triple-pane windows designed for noise reduction, acoustical wall and ceiling boards, acoustical ceiling and wall tiles, carpeting, insulation, commercially available coverings designed for noise control, framing double walls, or using commercially available vibration-isolation systems.

There are four basic principles of noise control, and you should have your home evaluated for the best fix:

Sound insulation

Adding sound insulation helps absorb the transmission of noise by providing a barrier to soak up and disrupt the noise. Try standard fiberglass, acoustic, or recycled cotton insulation. Use R13 in the walls and R19 in the ceiling.

Materials such as brick, thick glass, concrete, and metal all have high-density disrupting properties. Adding mass, such as double layers of drywall to a wall or ceiling, can help.

Sound absorption

Sound absorption materials include decoupled lead-based tiles, open-cell foam, and fiberglass.

Vibration dampening

The damping mechanism works by extracting the vibration energy and dissipating it as heat. A common material used to do this is sound-deadened steel or mass-loaded vinyl, which works great as a sound blocker on pipes in ceilings and walls. It is a dense PVC sheet loaded with barium sulfate or calcium silicate to add weight. It’s about one pound per square foot.

Vibration isolation

This prevents the transmission of vibration energy from a source to a receiver by introducing a flexible element or a physical break. Common vibration isolators are springs, rubber mounts, and cork. We see these items on AC units and other types of HVAC mounted systems to rafters in residential buildings. They are found in some household items like washing machines and high-end audio equipment. I hope this helps.

Rob Robillard is a general contractor, carpenter, editor of AConcordCarpenter.com, and principal of a carpentry and renovation business. Send your questions to homerepair@globe.com or tweet them to @robertrobillard. Subscribe to our free real estate newsletter at pages.email.bostonglobe.com/AddressSignUp.