Boiler vents - I must be missing something

28W

Recently, I've driven and biked past two large, multi-story condominium developments under construction. They both have what appear to be gas boiler vents for every unit. Each vent assembly has two pipes, which I assume are intake and exhaust. The pipes are right next to each other, as in maybe 8" to 10" of separation. In addition, they are both at the same height and angle. Here's my question: isn't this a recipe for re-circulation? Or is what I'm seeing dual-intake or dual exhaust?

SWEI

Intake and exhaust

for condensing furnaces, perhaps?  Is there a down elbow on one?  Could be installed later...

gennady

Distance

Distance between supply and exhaust in most cases must be no less than 12". But in new construction usually plumbers and engineers are ignorant in respect of proper boiler installation. So what you see is a least of their heating problems. It is called " builder grade" construction.

Jean-David Beyer

Distance between supply and exhaust in most cases must be no less than 12".

Gennady Tsakh said "in most cases". But in one case that I know of, my W-M Ultra 3, they specify the separation between the intake and exhaust, and it is pretty small. They even supply a template and a termination where, I estimate the separation is about 9 inches center-to-center. The idea is to avoid problems of wind shear: they want the wind to not change the pressure difference between the intake and the exhaust, so the blower in the combustion system always sees the same load. And keeping them close together pretty much ensures this.



They list several piping methods. In mine, the exhaust blows straight out, and the intake sort-of sniffs in from the side. But under some wind conditions the intake gets some exhaust for brief periods. This is usually when the system is running modulated all the way down and the exhaust speed is not very high.



In another option, the pipes are close together, but the intake has an elbow pointing down (i suppost to keep rain and snow out) and the exhaust about a foot higher and pointing to the side.