Posted by Harold Kestenholz - Hydronic Network on November 15, 2001 at 13:44:54:
In Reply to: national gas boiler hot h2o sys posted by john cook on November 15, 2001 at 10:56:24:
One purpose of the expansion tank is to provide a place for extra water produced by heating water as water expands and contracts with temperature. Within the 50F to 220F temperature range of a boiler system, water can expand to provide another 4% of the total water in the system. As the water volume is not the same from system to system, there is no way to know from a distance what amount of water is in your system. However, if you fill your system to 12 psig when cold, if the pressure does not rise over 24 psig when the system is hot so the 30 psig relief valve will not weep, then your system is OK.
If you do not hear gurgling in the system and all your radiators become warm, then you do not need to add more water. After fresh water is in your system for some time, the oxygen in the water has combined with iron to form rust. Then there is no more free oxygen to cause further corrosion, so you do not want to remove this deoygenated water to replace it with fresh water to rust your system further. It may be useful to take a small sample of the water yearly to make sure the water is not acidic. As long as the system is without leaks, so no more fresh water is replacing that lost by leaking, your water can remain neutral and beneficial to extending the life of the equipment..