Hissing sound in the wall but no visible leak in Calgary, what is it?

A hissing sound inside a wall with no visible leak is worth taking seriously, because the two most common sources are a pressurised water leak and a gas leak, and one of them is a safety emergency.

What the sound is likely telling you

If you smell rotten eggs or a sulphur-like odour alongside the hissing, get everyone out of the house immediately and call emergency services from outside. That combination points to a natural gas leak, which is distributed in Calgary by ATCO Gas. Do not switch lights, appliances or the furnace on or off, and do not look for the source yourself. Gas work in Calgary requires a certified gasfitter and a gas permit from the City of Calgary; a homeowner cannot obtain a gas permit unless they hold an Alberta journeyman gasfitter certificate.

If there is no gas smell, the sound is more likely a water supply issue. Pressurised water leaking through a small crack or pinhole in a copper or PEX supply line can produce a steady hiss even when no water is visible yet, because the drywall absorbs it before it reaches the floor. A partially closed or failing shut-off valve, a pressure-reducing valve (PRV) that is wearing out, or water pressure that is simply too high can all create a similar sound. Calgary's water is hard, and scale buildup inside fittings or valves is one possibility a plumber will check.

A few things you can do right now without opening the wall: check the water meter. If the dial or the small triangle on the face is moving while every tap and appliance in the house is off, water is escaping somewhere in the system. If your home has a pressure gauge near the main shut-off, note the reading for the plumber.

What a plumber will do

A plumber will use an acoustic listening device or a thermal camera to locate the sound source without opening the wall unnecessarily. If a leak is confirmed, the repair cost depends on what is leaking and where: a valve or fitting replacement is a straightforward job, while a pinhole in a supply line behind finished drywall adds access and patching time. Hourly rates in Calgary run roughly $85 to $150 during the day, with a common call-out fee of $50 to $150 on top. If the plumber finds the piping itself needs replacing, that is a separate conversation with a wider price range.

Permits and certification

Repairing or replacing a leaking fitting or valve without changing the pipe layout does not require a plumbing permit under the Alberta Permit Regulation. If the pipe itself needs to be altered or extended, the City of Calgary requires a plumbing permit. The plumber should tell you upfront whether the scope triggers one and who will pull it.

What to ask before work starts

Ask the plumber to describe what they found with the listening or thermal equipment before anything is opened. Get a written quote that covers the diagnostic, the repair scope, whether drywall patching is included, and the warranty on parts and labour. Confirm the plumber holds a valid Alberta trade certificate and, if any deposit is requested before the work is complete, that the business holds an Alberta prepaid contracting licence through Service Alberta.

Until someone has found the source, keep an eye on the water meter: it is the simplest way to tell whether the leak is still running.