All furnaces produce dangerous gases such as carbon monoxide as a side effect of combustion. The flue's purpose is to transport these gases safely outside of your house. Yet a restricted flue cannot adequately perform this function, and may result in the buildup of toxins in your air. If you would like to learn about what causes a restricted flue, read on. This article will teach you about two common sources of this problem.
First it may be helpful to explain a few things about how a flue operates. Your flue works by means of a principle commonly referred to as negative pressure. This simply means that the pressure inside of the flue must be less than the pressure of the outlet gases. When this condition is satisfied, a vacuum is created, thus sucking those gases up through the flue and expelling them.
A restricted flue is one whose pressure has become too great. This reduces--or even eliminates--the vacuum necessary for safe evacuation. As a result, those gases may begin seeping back out of the furnaces into the air of your home.
Inadequately Sized Flue Pipe
The most frequent source of insufficient pressure is a flue that simple isn't large enough to accommodate a particular furnace. This problem is often encountered when attaching a new furnace to a pre-existing flue. Always be sure to ask your HVAC contractor to calculate the minimum flue diameter needed when installing a new furnace.
To make this calculation, a number of different factors must be taken into consideration. These include not only the BTU rating of the furnace, but also the total length of the flue system and the design of the attachment pipe leading from furnace to flue.
Too Many Elbows
Sometimes even a flue that appears sufficient on paper fails to properly evacuate the outlet gases. This can be the cases when there are an excessive number of elbows--or right angles--present in the flue line. Generally speaking, the more elbows there are, the greater the pressure inside of the flue.
When an HVAC system is being designed, there are usually two elbows accounted for. Unfortunately, the physical structure of a particular house doesn't always allow for a flue to reach the outside with so few bends. In that case, it is necessary that the flue's width be greater, to help offset the increased pressure caused by the additional elbows. If this is also not possible, a powered ventilation system, such as an induced draft fan may need to be installed.
For more information, contact an HVAC company like Action Plumbing Heating & Air Conditioning Inc.