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Condensing boilers are water heaters typically used for heating systems that are fueled by gas or oil. When operated in the correct circumstances, a heating system can achieve high efficiency (greater than 90% on the higher heating value) by condensing water vapour found in the exhaust gases in a heat exchanger to preheat the circulating water.
The annual fuel utilization efficiency (AFUE; pronounced 'A'-'Few' or 'A'-'F'-'U'-'E') is a thermal efficiency measure of space-heating furnaces and boilers.The AFUE differs from the true 'thermal efficiency' in that it is not a steady-state, peak measure of conversion efficiency, but instead attempts to represent the actual, season-long, average efficiency of that piece of equipment ...
High efficiency condensing gas furnaces typically achieve between 90% and 98% AFUE. [3] A condensing gas furnace includes a sealed combustion area, combustion draft inducer and a secondary heat exchanger. The primary gain in efficiency for a condensing gas furnace, as compared to a mid-efficiency forced-air or forced-draft furnace, is the ...
A condensing boiler Hot water central heating unit, using wood as fuel. A central heating system provides warmth to a number of spaces within a building from one main source of heat. A central heating system has a furnace that converts fuel or electricity to heat.
So, for a boiler that produces 210 kW (or 700,000 BTU/h) output for each 300 kW (or 1,000,000 BTU/h) heat-equivalent input, its thermal efficiency is 210/300 = 0.70, or 70%. This means that 30% of the energy is lost to the environment.
In practice only boilers with fan assisted fuel/air circulation will have the modulating feature. The fan also mixes gas and air more thoroughly, so achieving more efficient combustion. If the boiler is of the high efficiency condensing type, high turndown ratios are feasible and the higher the turndown ratio, the more efficient it will be.
High-efficiency condensing furnaces condense the water vapor (one of the by-products of gas combustion) and extract the latent heat to pre-heat the incoming furnace airflow, using a second heat exchanger. [2] This increases the efficiency (energy delivered into the building vs. heating value of gas purchased) to over 90%.
Natural-gas (or bio-gas) condensing boilers and hot-air furnaces increase efficiency over standard hot-flue models. Standard electric boilers can be made to run only at hours of the day when they are needed by means of a time switch. [35] This decreases energy use vastly. In showers, a semi-closed-loop system could be used.