1:5:10:365 EcoTip Blog

April 22, 2008

:113 Prevent Back-Drafting

Filed under: :113 Prevent Back-Drafting — Tags: , , , , , — John Banta @ 12:28 am

Welcome to today’s 1:5:10:365 Tip for becoming a better steward for our home and planet.

1:5:10:113 EcoTip: Back-drafting is a serious condition that can lead to fire or carbon monoxide poisoning. It occurs when the gases for any combustion appliance or a fireplace flow into the house instead of up the chimney. It can be caused by some very simple mistakes especially in today’s very tight energy efficient structures.

http://www.epa.gov/iaq/homes/hip-backdrafting.html 

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 Additional Information

Suggested Review – :111, :112

 There are many forces that can work together to depressurize a home according to EPA these include: bathroom exhaust fans, kitchen range hoods, and clothes dryers and fireplaces. Other problems are “leaky return ducts near combustion equipment, leaky supply ducts outside the conditioned space, wind, and the stack effect (warm air rising in a building tends to depressurize lower areas). If these forces are great enough, they can work to suck air and combustion products back down the chimney or flue and into the house.”

Yesterday I talked about the importance of having doors properly undercut or a Return Air Pathway. Back-drafting is one important reason why!

Let’s say you have a balanced central heating system that has a single return air supply in a hallway and supply registers in each room. Furthermore you’ve just installed a carpet that fills the undercut under the door and substantially reduces the amount of air that can flow under the doorway. As long as the door is open, no problem, but when the door gets closed the air blowing into the bedroom can’t get back to the return. The bedroom becomes postively pressurized, but the rest of the home becomes negatively presurized. There isn’t enough air to satisfy the needs of the furnace system so air starts to flow from cracks and other available openings. In a leaky home, there is probably enough unintended air to satisfy the needs of the system, but when there isn’t enough air, the air has to come from somewhere like by back-drafting down the flue pipe for hot water heater or the furnace. If the furnace or hot water heater is in the house and doesn’t have an unblocked fresh air supply, the combustion gases can flow out into the living space. If the combustion gases have already been burned – the risk is carbon monoxide poisoning. If the gases haven’t been burned, they may ignite and cause a fire. this is just one of several dangerous back-drafting situations. EPA discusses more at: http://www.epa.gov/iaq/homes/hip-backdrafting.html 

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