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How To Remove Air From A Hydronic Hot Water Heating System

By Edited Nov 13, 2013 1 2

How To Remove Air From A Hydronic Hot Water Heating System, is an article that will help you to do just that. removing the air from a hot water heating system is a very logical procedure and once the principles are understood it becomes a very easy task. Without a little insight however getting all of the air out of your system can be frustrating and very difficult.

This article will not only walk you through the how to part of this job, it will also explain the physical properties and the reasons we must evacuate any air within the piping. A full understanding of how this type of system works will help you to understand your mission a little more thoroughly.

Hot water heating systems use a boiler to heat water under pressure. This water should be free of air at all times. This is not always the case. Sometimes air will infiltrate the system from any one of a lot of different possible ways.

Heating sounds like babbling brook

Symptoms of air being present in the system, will always be the sound of running water. You may hear a babbling brook noise running through the living room. Your bedroom may have a nice stream sound running through the baseboard heaters.

Although this may be peaceful and give you the impression your in the amazon, or up on a mountain, camping beside a babbling brook, it's not a sound you should enjoy because it is stealing your money and compromising the heating system within your residence.

Hot water heating systems will always incorporate a thermal expansion tank somewhere in the piping. This tank has a pre charge of air behind a rubber diaphragm and this can rupture and introduce the charge of air into the piping.

A simple test can tell you if your thermal expansion tank is bad. Tapping the tank on the top will produce a certain pinging sound. Tapping the bottom should produce a completely different pitched sound. One side should be full of water and dense sounding and the other side should be a hollow higher pitched sound because there should be only air within this portion of the tank.

Examples Of Thermal Expasion Tanks

If this tank sounds the same when you tap the top as when you tap the bottom then your tank has blown the diaphragm and introduced it's pre charged air into the piping. The tank will need to be replaced before the system can be re purged.

Another way that air can get into a hot water heating system is through a leak on the suction side of any circulator pump. When the system is called by a thermostat. The pump kicks on for that zone and a small amount of air can be sucked in when it starts. This usually happens right on the flange gaskets.

Leaking Circulator Flange

Replacing any leaking parts around the pump or any where within the system is imperative prior to successfully purging the heating. Once this has been assured then we can locate the purge setups and begin to get the air out of the piping.



The Key to Peace and Quiet

Auto vents will KEEP the system quiet

400 TACO 1/8 INCH air VENT 150PSI
Amazon Price: $10.40 Buy Now
(price as of Oct 23, 2013)
Taco auto vents are a reliable way to keep the air from re-establishing itself within the piping and boiler on a hot water heating system.

Locate The Boiler Purge Setups

Find your drain valves

Heating System Purge Setup
There are required valves and drains to perform a good purge of any heating system. Before these valves can be located an understanding of the piping arrangement should be gained. This will make accomplishing a proper purge possible. 

When this type of system comes on, or answers a call for heat from any thermostat, the pump for that zone is called by a relay and it begins to circulate water in one direction through that zone or loop. Heated water is pulled from the boiler by the pump and it is forced around a piping loop through the radiation and then back to the boiler to be reheated.

When purging a system we are going to be attempting to do the same thing only with city water pressure or a well pump depending on which your home has. We are going to use this water to push all the air out of the system.

Auto Feeder
An automatic feeder valve is installed in the city water supply or the line from the water main. It is adjustable from 12 to 25 pounds per square inch. This valve will have a lever that will increase the pressure once there is an open drain somewhere, this lever should be lifted straight up to push the water as fast as you can without exceeding 25 pounds.

The boiler has a pressure relief valve that will blow off water if it gets to thirty pounds. keeping this from happening will require careful monitoring of the pressure and opening the drain in the purge setup before you open the lever on the auto feeder to push in more pressure.

In order to accomplish this we must be able to control where the water where pumping in goes. This is done by installing ball valves or shutoffs in the piping so they can be turned off and make the water go around the loop in the direction we want. This ball valve is then accompanied by a drain valve just before the water gets back to the shutoff.

We can then close the ball valve, hook a hose to the drain and push water using the city pressure or our well pump through the loop in a complete circle and then out a hose attached to the drain. Water is pushed around and then out and all of the air will eventually go with it. The valve can be momentarily opened to relieve any air between the shutoff and the drain and then closed again to reverse the direction.

When you run the hose outside or to a drain of some sort the end of the hose can be placed into a five gallon bucket and observed for air bubbles. When the flow is solid and there are no more air bubbles coming out then you have a solid liquid loop and the valves can be closed for that zone.

Each zone on your system must be purged individually untill all of them are free of any air. It is recommended to start with the zone that runs the farthest away from the boiler. Work your way back to the closest zone.


Thermal expansion; The Boilers Natural Enemy

A good working properly sized expansion tank is a must

AMTROL 60 EXTROL Expansion Tank - 7.6 Gallon
Amazon Price: $78.50 Buy Now
(price as of Oct 23, 2013)
Amtrol makes all sizes and has a reputation behind them. These tanks will offer years of trouble free service.


Nov 9, 2012 10:31pm
Very nice article I want to try this to my farm...
Nov 9, 2012 10:31pm
Very nice article I want to try this to my farm...
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