by William Collins

Created on: December 15, 2009   Last Updated: December 18, 2009

Hydronic heating systems use circulating hot water to heat your house. The device that heats your room is the radiator, when you don't feel much heat radiating out of it you will need to "bleed" or remove the air out of it. This is not a difficult job.

The radiator should normally be full of hot water, if it's not then your room will get cold. To check if it needs to be bled, feel the radiator to see where the warmth is. If the bottom of the radiator is warm but gets colder toward the top, then you need to get the air out so it can fill with hot water.

First, you need to make sure the heating system is off. Each radiator in your house has a small bleed valve that you open to let the air out. It's located at one end of the radiator, near the top. This little valve will most likely be painted over in some of the older houses, you will have to scrape off the paint before you can open it.

You will need a small bleeding tool, available at most hardware stores or heating jobbers, it has a square hole at one end and a butterfly for your fingers at the other. It looks like an old roller skate key.

Begin bleeding with the radiator closest to the furnace, then the next closest and so on; bleed the furthest one last. Before you open the bleed valve, make sure you have an old towel to catch the water that comes out.

Insert the bleed tool and turn it about 1/2 turn counterclockwise. You'll hear a hissing noise as the air escapes. When the bubbles stop and you see water coming out, close the valve, you're done with this one. Go on to the next radiator and so on until you're done with the farthest one from the furnace.

You should be aware that there are two types of hydronic systems. An open system and a closed system. Each system has an expansion tank—a tank that's half-full of air that allows for expansion of the water as it heats up. The terms "open" and "closed" refer to this expansion tank.

In the older system the expansion tank is open to the atmosphere and has an overflow drain that empties on the roof if it's overfilled. If your house has the older open expansion tank you will have to make sure that it has enough water in it.

The expansion tank is usually located in an upstairs closet, higher than the radiators. To fill it, look for a small sight glass that shows the water level. Next to the tank, there will be a water valve that you open to fill it. Close the valve when you see the water in the sight glass.

The closed expansion tank system has an automatic filler that keeps the system full.

Bleeding heating radiators is an easy procedure that you should do a couple of times every season to get the most efficiency out of your  hydronic heating system.

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