What is the difference between a condensing and non-condensing boiler?
All boilers under certain conditions will condense. The difference between a condensing and non-condensing boiler is that a condensing boiler is designed to operate and survive long term in a condensing environment. A non-condensing boiler will not last as long, because condensate is corrosive.
The condition that causes a boiler to condense is reduced flue gas temperature. The point at which condensing will occur, also called the dew point of the products of natural gas (or propane) combustion, is about 130F. Above this temperature, the moisture entrained in flue products as water vapor will remain vaporized. Below this temperature, the water vapor will change phase and condense out of the flue products as liquid. When this phase change occurs, additional energy is released that is beyond the sensible heat of the flue products. In a boiler, this phase change occurs on a heating surface and the released energy transfers through the heating surface into the boiler water on the other side. By capturing this energy, which is lost out the exhaust stack on a conventional system, a condensing boiler gains efficiency, thus making it much more efficient.
Naturally, the products of combustion cannot be reduced in temperature to 130F unless some of the heating surfaces in the boiler are also less than or equal to 130F. The only way to accomplish this is to have an entering boiler water temperature of less than or equal to 130F. Simply stated, if return water to the boiler is higher than 130F, condensing cannot occur; even if the boiler modulates and is at its lowest firing rate. This is determined by the laws of physics. The highest achievable efficiency that can occur without condensation forming inside the boiler is approximately 87%.
To see our non-condensing and condensing boilers click on the link below...
http://www.houseneeds.com/heating/hydronic-heating-boilers
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