Why Are My Pipes Making That Awful Noise?

​Editor's note: This post has been updated to include sources and instructional videos.

The cold is upon us yet again, and with it comes that incessant clank from inside your walls. Every. Damn. Night. It's impossible to sleep without running the heat, but the sound of tiny sledgehammers inside your pipes is exactly what's keeping you awake.

It may feel like a cruel joke that the weather is playing on you, but it's just a simple problem of fluid dynamics. So what's the source of this awful racket and, most importantly, how do you make it stop? First, a little background.

How Does Heating Work?

Any modern structure has some sort of HVAC (heating, ventilation and air conditioning) system installed, but there's a lot of variation in how fresh air of the desired temperature gets to you. Focusing on the first letter of that acronym, heat can be transferred through air, water or steam. If you have a furnace where you live — congratulations! You have a heated air system, and this never happens to you. The rest of us are jealous. Back to the problem at hand…

The heart of hydronic (water or steam) systems is a boiler, which is essentially a big metal cylinder with water in it, a gas, oil or electric line feeding into it and some tubes jutting out of the top.

Depending on which you have, the water in the boiler gets heated into steam or hotter water, which usually gets pumped from the boiler to a series of pipes installed throughout the building — although some older buildings don't have a pump at all and rely on gravity to do the work. These pipes lead to radiators or other heat exchangers which heat the room, and the now-cooled water or steam heads back to the boiler to start all over again. If you don't see a big hulking radiator nearby, it likely means you have baseboard heating.

Okay, But Why Is That Noise Happening?

Boilers and pipes are sturdy things, but that also means the heating in most buildings is quite old, and age allows things into those pipes that don't belong there. For water pipes, that usually means air, and in steam pipes, ironically, the problem is water.

Pipes sag over time. When that happens (or if they weren't installed properly) steam can condense back into water which has no way to drain back down to the boiler. Passing steam then picks up these drops of water and hurls them at high speed into the nearest pipe fitting, causing a loud, hammering sound. This is called — for obvious reasons — steam hammer.

A similar problem happens in water pipes when air is trapped in the lines, causing a rattling sound that's every bit as irritating. At its worst, trapped air will keep water from flowing, resulting in parts of the building getting not heat at all. 

So What Can I Do About It?

Disclaimer: Although these are the most common causes of weird pipe noise in the winter, they're far from the only culprits. If you're not confident in your ability to repair pipes, this might not be the best time to try DIY fixes. In fact, in many places it's illegal to repair your own boiler — not to mention dangerous. There is no shame in calling a plumber.

That said, here are some potential solutions.

For steam systems, noisy, sagging pipes need to be adjusted or replaced. You should also make sure that the boiler has the correct amount of water in it: too much and it won't heat your home properly, too little and it can weaken or explode.

In the event of air trapped in a water heating system you can "bleed" the system, meaning you allow water to flow out until it takes all the air with it. 

If that fails, arrestors or air scoops can be installed: the former acts like a piston and keeps water from clanking during big pressure changes while the latter removes passing air from the system.

Either system is prone to noise due to mineral deposits and other gunk, which can obstruct steam or allow air to cavitate in a water system. Likewise, keeping boilers running at the proper pressure is crucial, for your safety and sanity.

Home maintenance is one thing, but if you live in an apartment building, chances are you don't have access to your boiler. The good news: noisy pipes become your landlord or super's problem. The bad news: that same landlord refused to fix your shower for weeks and isn't likely to care about some clanking. Thusly armed with knowledge, feel free to remind him or her that, while loud pipes might seem like a small gripe, they're a sign of a failure somewhere in the building's HVAC system which will only get more expensive to fix the longer it's allowed to continue.