Exhaust Duct

 Many homes in the United States depend on gas furnaces to heat their homes in chilly winter months. This is because gas furnaces are quite efficient in generating heat that is enough to beat the cold. The heat pumps which are also used in moderate climates will not work well if the temperature dips below zero degrees. This is because it will not be able to source heat from the environment. However, to ensure that your gas furnace is functioning efficiently and safely an exhaust duct should be connected to it. This will vent out the toxic gasses and other byproducts that result from combustion. The flue system is also a safeguard against fire. If the wastage gases come in contact with some combustible product, they can lead to fire which can set the house and it occupants at peril. Here we will discuss the major types of exhausts systems for gas furnaces.

 Natural Vent

This is a very common type of vent system in houses that have gas furnaces. It is also referred as the Type B vent. It works on the principle of natural convection. Type B vents are a standard design that most modern gas furnaces use. These vents draw air from inside the house for combustion. Once the combustion takes place, hot gases are produced. The hot gas being lighter quickly rises through the vent and is exhausted out. These flues are set vertically to expel combustion air through the roof.

They offer some advantages such as installation is quite easy and cost effective. However the main demerit of this type of exhaust system is that they are quite liable to back drafting. Exhaust gases can find their way back into the air distribution system. This often becomes the root cause of carbon mono oxide exposure.

 Direct Vent

Direct vents have a pair of pipes one big another small. The big pipe is used to extract air from outside for combustion. The air will be blown across the heat exchanges to get heated. It will then be released into the room as warm air via the fan. The smaller pipe is used to vent exhaust gases of this ignition process. The pipes are set both horizontally and vertically. Horizontal setting allows the gases to be exhausted through a sidewall. Vertical installation can also be done to let the gases out through the roof. The main advantage of this type of vent system is that you do not need a chimney whether horizontal or vertical installation is used. It is quite easy to install. Direct vents also cause less environment pollution as they tap most of the combustion heat. It has alow risk of backdrafting.

  Sidewall Power Vent

This type of vent system is also referred as induced draft fan. A fan is fitted at the end of exhaust duct to draw the combustion gases and expel them out. The fan works in tandem with the furnace. In fact it starts running as soon as the furnace is powered on. These systems are great to eliminate cumbersome chimneys that we see in old houses. They are affordable and rated high for their safety and efficiency.

 Which duct is better for your gas furnace- through the roof or sidewall?

Well, this depends solely on the AFUE rating of your furnace. If the rating is below 90 percent, you should opt for an exhaust system that goes up through the roof. This is because the combustion byproduct would be in the form of gases. The wastage gases will float through the flue and go out.

If the efficiency is above 90%, the sidewall vents are better. This is because in this kind of furnace there is a second heat exchanges. They are also called condensing furnaces. The furnace sends the exhaust gases from the first heat exchanges to the second one. Here the gas is condensed to extract all the remaining heat. The condensate is vented out. The draining of the liquid will happen better with a sidewall flue.



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