How to Bleed Air from a Heating System | Using Air Bleed Valve

How to Bleed Air from a Heating System 

Boiler systems that distribute hot water to baseboard radiators throughout the home are popular in many parts of the United States and offer energy-efficient heating to keep your family warm all winter. When things go wrong, however, it can be difficult for homeowners to confidently diagnose issues with these systems.

One of the most common problems these systems have is a buildup of air that creates odd sounds coming from the baseboards and inadequate heating. Luckily, bleeding air from a heating system is a simple HVAC process that many homeowners can perform on their own

What Is a Hot Water Baseboard or Radiator Heating System? 

Called hydronic systems in the industry, these tightly sealed systems start with a boiler that sends hot water to radiators or baseboards throughout the home. The hot water gives off radiant heat and then circulates back to the boiler to be reheated. In-floor variations are becoming more popular but are still less common than traditional options.

Also known as boilers or simply radiators, hydronic systems can be powered by electricity, heating oil, natural gas, or propane.

The Three Main Reasons Why Air Builds Up in Radiators 

There are three main causes of air buildup in radiant heating systems:

  1. The water pump was installed above the water supply tank.
  2. Hydrogen has built up in the system due to the presence of rust in the piping.
  3. Leaks have caused air to enter the system and become trapped. (This is more common if the boiler is re-pressured.)

Signs Your Hot Water Heating System Needs an Air Purge

While it can be difficult, it’s important to listen for the tell-tale changes in the sounds your boiler and radiator or baseboards make when they are turning on, running, or shutting off. The signs of air buildup are:

  • Noisy gurgling or odd clunks.
  • A sound similar to water draining or running from pipes.
  • Rooms feeling colder than normal or baseboards not heating up normally.

Manual and Automatic Bleeder Valves

There are two types of bleeder valves for hot water heating systems:

  1. Manual Bleeder –These are manual valves homeowners can turn on to release air. They are often located where the air is most likely to collect, usually above the boiler or at the line's highest point. When you notice the sounds associated with air buildup, simply follow the steps in the next section to use the bleeder valve.
  2. Automatic Bleeder – This is a passive valve that reacts to air buildup over time. When the additional pressure in the line hits a certain point, it forces open the valve to let air escape. These valves can fail, so you may need to check or even replace yours.

A trained HVAC technician can retrofit existing systems with these valves, depending on your needs.

How to Remove Air from a Baseboard Heating System

Follow the steps below to use your manual bleeder valve. Whether your home is heated by radiators or baseboards, these steps will largely be the same:

  • Turn your boiler to the highest setting and allow your radiator or baseboards to heat up. This should take 15 to 30 minutes. When it feels hot, turn off the entire system.
  • Go to the radiator (or baseboard) nearest the boiler and identify the air bleeder valve. The valve is typically located on the top of the radiator or piping and will require a flathead screwdriver or an air valve key, which is available at any hardware store.
  • Place a container below the valve to catch water and have a towel ready. Slowly open the valve; some water may drip, but any trapped air will also be released. You will likely hear a slight hissing sound when you first loosen the valve, which is an excellent sign that trapped air is being removed from the system.
  • When no more air comes out of the valve, close it completely.
  • Repeat these steps at every radiator (or baseboard) valve in your home. It’s usually best to go from the radiators closest to the boiler to those located farthest away.
  • When all radiators or baseboards have been “bled,” check the gauge on the boiler to ensure the water pressure is normal (typically 1.5 to 4 BAR) and turn on your heating system.

If these steps don’t eliminate the issues you’ve observed, it’s time to call a professional for assistance.

Keep Your Cool with Professional Hot Water Heating System Repairs

The easiest way to address air build-up in your heating system includes a single step and a single tool. Grab your phone and call One Hour Heating & Air Conditioning. A professional HVAC technician will inspect and repair your boiler and hot water heating system the right way. Call (800) 893-3523 to request an appointment today!