How to Bleed a Radiator

When those cold nights come, you want to ensure your heating system performs at a higher efficiency lowering heating costs and saving you money. By bleeding your radiators in your home at least once a year, you can make that happen with simple techniques to take the air out of the system. How to Bleed a Home Radiator?

  • Check the Boiler pressure gauge
  • Crank up the heater until radiators are hot
  • Turn off heater
  • Use Gloves & Safety Glasses
  • Open bleeder valves on each radiator-start closest to the boiler & bleed the air out until a hissing sound turns to a water stream
  • Power up
  • Check boiler pressure
  • Check for cold spots on radiators

The air in your radiators, whether they are cast iron or baseboard, can acquire air that is trapped in pockets along the heater lines feeding the radiators. They can cost you over time, so why not learn to use the bleeder valves and keep them free of air, making them much more efficient?


What Happens When You Bleed a Radiator


When small air pockets develop in your home’s radiator system, they can block the water from moving around the system, keeping the room temperature in your home cold. This wastes energy as the heater struggles to catch up to the thermostat setting. With the cost of oil or electricity on the rise every year, everyone needs to save money on the smaller things that lead to saving money. With heating systems, especially older ones, the less the heater runs, the more money you can save.

If you have some radiators in your home that are cold by touch or cold at the top or bottom after your systems have been running for a while, you may just need to bleed your radiators to improve your systems’ circulation by taking these air pockets out. Air pockets trapped in the pipes and radiators prevent them from being efficient, tuned up, and operating right whether your home is old modern, or in between.

Can you Bleed a Radiator When The Heater Is On


When you’re ready to inspect your radiators for air, crank up your heating system and let the radiators heat up for a while. Let them heat up to the maximum. This will ensure that when you do open them up after you shut the heater down, you’ll know that the heater’s water will be circulated all through the systems pipes and all the radiators that are online from the furnace. So it’s important to run the heater red hot than when you’re ready to shut it down. Let the Radiators cool down some. You want to get going so the pressure and heat are maxed so you can get all the air out.

Some tools you will need are:

  • Protective Gloves to protect your hands from hot water
  • Protective Glasses that can protect your eyes in case of hot water
  •  A small bowl or container to use for draining the system
  • A radiator key (or, alternatively, a screwdriver or a pair of needle-nose pliers)


Which Radiator to Bleed First


Do all of your radiators start from the ground floor up?

  1. Check and make sure the Heater is off.
  2. Check each radiator for cold spots by running your hand over the top and bottom of each radiator (be careful not to burn your hands)
  3. If you find a cold spot on a radiator, that radiator will need to be especially bled.
  4. Find the radiator’s bleed valve on the radiator. This is usually located at the top of one side of your radiator.
  5. Once you find it, you will need a Radiator Key to perform the bleeding
  6. You can use a screwdriver if you can’t locate a Key
  7. Use a small towel while holding the Key and turn the key counterclockwise and bleed the Radiator
  8. You will hear a hissing sound as you bleed the air out
  9. Once the air turns to water, start to close down the valve with the Key
  10. Continue and bleed the rest of the Radiators online

Once you have bled all the radiators, check the Boiler/Heater and make sure that the pressure on its boiler’s controls is back to normal working pressure. If the pressure is normal, you can switch your heater and check that there aren’t still any cold areas.


How to Bleed a Hot Water Radiator


  1. Record the pressure of the system at the Boiler
  2. Turn off the power to the Boiler to the system and record the pressure
  3. Open all of your zone valves that run to each of your heating zones.
  4. Close all of the shutoff valves to these zones
  5. Attach a length of garden hose to a drain spigot on the return line that runs to your boiler. Direct the garden hose to a floor drain or bucket.
  6. Open the auto-makeup valve and the spigot to which the hose is connected simultaneously. Allow the water to drain out of the hose until no more air bubbles are seen.  Keep an eye on the water pressure, and do not allow it to rise above 25 psi. If it does, release the auto-makeup valve momentarily until the pressure drops.
  7. Release the auto-makeup valve and close the spigot.
  8. Repeat Steps 3 and 4 for each zone in your system.
  9. Close each zone valve and open all of the shutoff valves. Verify that the water pressure is the same in the system as it was before you bled out the lines.
  10. Turn the power back on.

Some Baseboard Radiators have air bleeders on the ends of the corners or at certain lengths that are easier than this setup. Remove the cover at the end and use a screwdriver or a pair of pliers, depending on whatever tool is called for.

Bleed the air from there as often as you could. Baseboard pipes can cause quiet banging sounds, gurgling, and trickling sounds that can drive you crazy, no matter how old the house you are living in. With this technique, you can lower your heating bill and quiet the house down just a little.





How Often Should You Bleed Radiators


It’s a good idea to bleed your radiators regularly, even though you may not hear air or get any cold spots on the system’s radiators. Any loss in the circulation of hot water will reflect on an efficiency loss of the heating system, and that will reflect on the energy used, which equates to money used to heat the space you are in. This space is measured and calculated for the proper amount of radiators needed to heat the building, room, or space. That efficiency is lost if there is air in the radiators.

Follow the basic guideline of one pound of pressure for every two feet of rising, which, for a standard two-story house, translates to about 12 psi to 15 psi. Keep tabs on the system, which will save you money in heating costs over time.


Waterproofing an exterior wall of this old house seemed like an impossible feat, but with sound advice and plenty of help, I could fix this massive water problem. Read about this in an article I wrote on MyWaterearth&Sky called  10 steps For Waterproofing An Existing Outside Wall.










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