e.alleg wrote:I think I heard that below a certain temp the gases will condense and rot out the steel? I know that the heat from the registers and the domestic hot water is just as hot when the boiler is at 150 degrees as it is when it's up around 200
I think what you are talking about here is oxygen. At 150*, there will still be quite a bit of oxygen entrained in the water. This can eat your boiler's metals. If you run closer to 200*, it will drive the oxygen out of the water and reduce your corrosion considerabley.
However, this applies to commercial/industrial applications more so than residential systems as the oxygen comes in with the feedwater. Since your home system may take on a quart or gallon of water every year, incoming oxygen is hardly a problem. In a commercial application, say a laundry, where massive steam losses are the norm, thousands of gallons of fresh water daily can bring in many pounds of entrained oxygen. Untreated, the boiler would dissappear quickly.
I wouldn't worry about it as long as the waters temperature is heating your home, your probably safe from the evils of oxygen.