All About Furnaces and Duct Systems. UPDATED on October 2, 2. Many different appliances can be used to heat a house, including boilers, water heaters, heat pumps, and wood stoves. However, most homes in the U. S. are heated by a forced air furnace. These devices are connected to ducts that deliver heated air to registers throughout the house. Different types of furnaces are manufactured to burn a variety of fuels, including natural gas, propane, oil, and firewood. Disadvantages Of Manual Hr Systems' title='Disadvantages Of Manual Hr Systems' />The most common furnace fuel in the U. S. is natural gas. In Europe, where furnaces are almost unheard of, most homes are heated by a boiler that distributes heat through hot water pipes. Unlike Europeans, however, most Americans insist on central air conditioning in their homes. Its easier to provide whole house air conditioning in a home with a duct system. Once you have a duct system for cooling, its cheaper to install a furnace for winter heating than to install a boiler with a separate distribution system. Even though the smallest available furnaces are often oversized for a high performance home a problem I addressed in a 2. Heating a Tight, Well Insulated House furnaces still have virtues that are hard to ignore. They are inexpensive, widely available, and easily serviced by local HVACHeating, ventilation, and air conditioning. Collectively, the mechanical systems that heat, ventilate, and cool a building. Management Systems International MSI, a Tetra Tech company, is a USbased international development firm that specializes in designing, implementing and evaluating. For many North American homes, they are a logical way to supply space heat. Defining AFUEWhen it comes to fuel efficiency, residential furnaces in the U. S. are divided into two main categories so called medium efficiency furnaces and high efficiency furnaces. Furnace efficiency is usually calculated using a laboratory procedure that measures an appliances annual fuel utilization efficiency, or AFUE. This calculation accounts for heat losses up the chimney, heat losses through the appliance jacket, and heat losses due to on and off cycling, but it doesnt account for electricity use fan energy use or heat lost through the distribution system ductwork. AFUE can be calculated for boilers as well as furnaces, and is used for appliances that burn many different types of fuel. Low efficiency and medium efficiency furnaces. The usual definition of a low efficiency furnace is one that is less than 7. The reason that you can no longer buy a low efficiency furnace is that the federal government now requires residential gas fired furnaces to have a minimum efficiency of 8. The minimum efficiency for oil fired furnaces is 8. Medium efficiency furnaces have efficiencies in the range of 8. The line between mid efficiency and high efficiency furnaces is not arbitrary, but marks the division between appliances with distinct operating characteristics. Introduction to Chemical Engineering Thermodynamics Solution Manual Ebook download as PDF File. Text File. txt or read book online. Human Resources Management HRM Training Courses Online Selfstudy Distance Learning Courses. This is the first Article in our new Course HVAC2 Electrical Rules and Calculations for AirConditioning Systems, which will list, explain, and discuss with. AUTUMN 2012. ISSUE 51. Price 10. 00. International HR Adviser The Leading Magazine For International HR Professionals Worldwide. Global Mobility Technology The. Mid efficiency furnaces are designed to keep flue gases hot enough to avoid any condensation of flue gas moisture, while high efficiency furnaces deliberately encourage the condensation of flue gas moisture. It is technically difficult to manufacture a furnace with an efficiency between 8. Furnaces with in between efficiency have sporadic condensation of flue gases, and this condensation causes corrosion problems. Furnaces with an efficiency of 9. PVC pipe, a material which is more resistant to corrosive condensate than the stainless steel vent pipe that would have to be used for the hotter flue gases that would occur in a furnace with an efficiency in the tricky 8. LXJ0lhN2g/hqdefault.jpg' alt='Disadvantages Of Manual Hr Systems' title='Disadvantages Of Manual Hr Systems' />High efficiency furnaces. High efficiency furnaces also called condensing furnaces have AFUE ratings that range from 9. These furnaces have a secondary heat exchanger. Device that transfers heat from one material or medium to another. An air to air heat exchanger, or heat recovery ventilator, transfers heat from one airstream to another. A copper pipe heat exchanger in a solar water heater tank transfers heat from the heat transfer fluid circulating through a solar collector to the potable water in the storage tank. This phase change from water vapor to liquid water releases heat, improving the units efficiency. Condensing furnaces must be hooked up to a drain that can dispose of the liquid condensate. A high efficiency furnace costs more than a mid efficiency furnace. However, the venting system for a high efficiency furnace may cost less than the chimney required for a mid efficiency furnace. Most condensing furnaces burn either natural gas or propane. While condensing oil fired furnaces exist, the devices have a mixed reputation. According to some HVAC specialists, oil fired condensing furnaces require frequent cleaning. Single stage, two stage, and modulating furnaces. The simplest furnaces are single stage furnaces with single speed blowers. If the furnace is rated with an output of 6. Btuh, that is the furnaces output whenever it is running. More sophisticated two stage furnaces can operate at two different output levels. Most of the time, these furnaces operate at a lower Btuh output the higher output is only needed on the coldest days of the year. Modulating gas furnaces are more sophisticated than two stage furnaces. They include an automatic fuel valve that varies the amount of fuel delivered to the burner. Many modulating furnaces also include a variable speed blower motor usually an electronically commutated motor, or ECM which like the automatic fuel valve ramps up and down in response to heating demand. Since modulating furnaces can match the heating demand precisely, they provide more even heat than single speed furnaces which operate with a stop and go jerkiness. Oil burning furnaces are less flexible than gas furnaces. While its fairly easy to design a gas valve which varies the amount of fuel delivered to the burner, oil burners have a nozzle that is optimized for a single firing rate at a fixed Btuh output. Thats why oil furnaces are usually single stage furnaces. Condensing furnaces are power vented, so they include at least two fans an air handler fan that distributes warm air through the homes ductwork, and a power vent fan to move exhaust gases through the flue pipe. Most, but not all, condensing furnaces are sealed combustion furnaces meaning the burners pull outside air into the combustion chamber through plastic ducts to feed the fires needs. Sealed combustion furnaces dont use any indoor air for combustion. The main advantage of a sealed combustion furnace compared to an old fashioned atmospherically vented furnace is that a sealed combustion furnace is much less likely to suffer from backdrafting. Indoor air quality problem in which potentially dangerous combustion gases escape into. Backdrafting occurs when a powerful exhaust fan for example, a range hood fan depressurizes a house enough to draw combustion fumes down the chimney and back into the house. Elnec Beeprog Driver. For more information on this issue, see Makeup Air for Range Hoods. A low thermostat setting may void your furnace warranty. Energy advice columnists routinely advise owners of vacation homes to turn down their thermostats when the homes are unoccupied. For example, the Home Energy Saver Answer Desk at a website maintained by the Environmental Energy Technologies Division at Lawrence Berkeley National Laboratory was posed this question by a reader How can I save energy in my second home, which is unoccupied a large part of the yearThe LBNL experts responded, For cold climate homes, turning the heat off or at least way down while away is a natural starting point.