Concentric Vents and Blizzard Nemo

by Erik North on July 31, 2013

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Blizzard Nemo clobbered Maine and most of the eastern seaboard this past February. Snow blanketed the entire coast, piling especially high in the Appalachian foothills. We slogged through a three foot dump in Portland. 50 MPH gusts whipped snow every way, sculpting enormous snow drifts in almost alien landscapes.

That’s what our family woke up to that Saturday morning. One area of our lawn had been scoured clean of snow while fifteen feet away, a snow drift obscured the first three feet of the house’s first story windows. I was part way through my morning coffee, shaking out the cobwebs when *oh, crap* gas heating systems! I quickly dashed off a couple dozen emails to customers with gas heating systems. What was the big, hairy emergency?

Gas Heating Systems and the Big Hairy Emergency

That’s going to be the title of the new Harry Potter series. I blasted out a group of emails to folks who owned direct vent gas heating systems (oil systems can have direct vents but it is much less common). These systems use concentric vents that expel combustion exhaust and draw in fresh combustion air with the same vent pipe.

A concentric vent is exactly that: A pipe with a smaller exhaust pipe inside, running down the center. If you to look at it straight on, the pipe appears like a pair of concentric circles.

Direct vent gas heaters like combi-boilers, on demand hot water systems or monitor heaters have concentric vents (or something very similar). These vents are located on the exterior, 2 to 4 feet off the ground. Now, about those 8 foot snow drifts…D’oh!


You can see where this was heading. With the massive snow drifts, people with direct vented gas heating appliances could potentially have their vents blocked. This would prevent proper combustion as the unit would be starved for oxygen, unable to pull in outside air. The exhaust would also be blocked, possibly backing fumes into the house. This was an extraordinarily dangerous and potentially fatal danger from carbon monoxide and exhaust fumes.

Direct vent heating appliances with concentric vents are apt to become more common as building enclosures become tighter. The possibility of the exhaust pipes being choked for air, even during once a decade blizzards, needs to be kept in mind.

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