Steam boiler efficiency is a concern of owners who use hydronic boilers. Simply put, it is how well the boiler supplies heat relative to its cost. Selecting a high-efficiency steam boiler and regularly maintaining it is key to maximizing efficiency.
The Steam Boiler
Steam boilers work by heating water (or other liquid) to a set temperature until it turns to steam. The steam from the boiler is generated by means of several fuel sources (coal, oil, wood, natural gas, or electricity).
The heat created by the steam boiler is transferred through pipes, which displace it by way of radiators, baseboard heaters, or floors. Older homes (pre-1950's) have steam radiators, which actually use steam. Most of today's radiators operate by hot water or gas.
An Efficient Choice
Choosing the right steam boiler will have a big impact on performance. Boilers that have burners with a high pressure drop design, simple linkage assemblies, and quality fan and damper designs will operate better and are easier to tune (maintain). A boiler with a four-pass design provides four opportunities for heat transfer. This gives it higher efficiency at a lower fuel cost.
Other measures are flue gas temperature (stack temperature), fuel specification, excess air, ambient air temperature, and radiation and convection losses. The ability of a steam boiler to deliver the required air-to-fuel mixture and maintain it over time will determine efficiency. This relates to the combustion efficiency or the boiler burner's ability to burn fuel. High amounts of unburned fuel and excess air are inefficient.
Steam Boiler Water Quality
Since steam boilers use water to supply heat, it is a major part of the system. As such, the quality of the water you put in will have a direct impact on heating efficiency. A water analysis can identify the composition of your water to determine its "hardness." Water hardness is a measure of mineral contamination. This is done by a chemical analysis or electrical current. If water is called "hard," it has a high mineral content.
The primary cause of fouling in boilers is water hardness. This creates scale or the crystallization of solid salts, oxides, and hydroxides. Scale can cause your steam boiler to work harder, reducing and blocking the flow of heat and increasing pressure. Treating your water can minimize the formation of scale.
Three methods exist for treating your steam boiler's water. Internal treatment conditions the water with chemicals (scale inhibitors). Demineralization (also known as reverse osmosis or electrodialysis) replaces inorganic salts by ion exchange, and deaeration involves atomizing water with steam to remove dissolved oxygen and carbon dioxide.
The combined use of water treatment methods will ensure deposits do not reduce steam boiler efficiency. This not only prolongs the life of the boiler by causing it to work less, but also increases efficiency by consuming less fuel. Choosing an efficient boiler design will naturally yield greater benefit, but will also make it easier to maintain. And the savings from an efficient boiler design can far exceed its initial cost.