In order for your furnace to properly heat your home, the temperature in your heat exchanger need to reach an extremely high level. Just because you set your furnace at 75 degrees Fahrenheit, that does not mean that the air in the furnace is itself that same temperature. Heat exchangers instead are heated to an extremely high temperature and that air is distributed through the house but quickly cools to a more manageable temperature as it arrives through your air ducts.
The heat exchanger is the wall or tube that is heated when the burners in the furnace are ignited. Ignition occurs when the home's thermostat reads the air temperature and determines it to be less than the desired setting. This sends a signal to the furnace to ignite the burners and heat up the heat exchanger. The heat exchanger itself is the part of the furnace that the cool air passes over to heat up.
Temperatures in the heat exchanger in a residential heating system can reach upwards of 175 degrees F. The temperature needs to be as high as possible because these forced air systems heat cooled air as quickly as possible so that it can be distributed quickly throughout the house via the blower. The blower usually kicks in at about 135 degrees so that the warm air can be distributed to reach the desired temperature in the home.
The one major problem that can develop in the heat exchanger is that it will eventually crack over the course of time. This is normal for most heat exchangers and is inevitable due to the nature of the material and the process. Heat exchangers are made of metal that will normally expand and contract over the course of time as it is heated and cooled. Due to the extreme variances in temperature, the heat exchanger will eventually crack. It is usually just a matter of when.
The temperature rise in the heat exchanger is important. Desco Energy notes that the range of temperatures that the heat exchanger experiences needs to be within the range specified by the manufacturer. Typically, the rise in temperature is somewhere between 40 and 70 degrees F. Having the proper temperature will save up to 2 percent in annual fuel costs.
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