House has an oil-fired boiler with a powervent flue, and someones
home-grown attempt at supplying outside air for combustion (4" flex
hose that was shoved over the end of the air intake on the burner
If it makes sense for this to have an outside air intake for
combustion, I'll have it done properly (the hose slipped off this past
weekend and revealed itself for the kludge it is), but since it has a
power-vented flue and is therefore sucking large amounts of indoor air
through the damper and out the flue, what sense does it make to worry
about the small amount of air the combustion intake is going to pull
out of the house?
Or, is the power-vent flue setup done wrong as well?
: But, is there any benefit to using outside air for combustion
: much inside air is being pulled through the damper?
That's going to depend on a few different things, including how
air tight the house/basement is. I respectfully suggest you
should have someone in to check it out. Negative pressure in the
basement can pull gases from the fire into the air and thus into
the ducts. It's hard to quantify without being t here.
Unless I do not understand your system, the air pulled through the damper
and out the flue by the power vent IS combustion air. Combustion air can be
supplied from the inside ambient air or from outside. An outside air supply
should prevent any inside air from going outside, except for various air
leaks, of course.
I'm not saying this setup is correct, its just what was there when I
bought the place:
The flue has the typical round weighted swinging damper-door
arrangement, and when the power vent is active (when the boiler is
firing) the damper door swings wide open and lots of my garage indoor
air gets sucked outside by the power vent, along with the flue gases of
So, with all that inside air getting pulled outside, what's the point
of trying to use outside air for combustion?
The unit is maintained, cleaned, and inspected by a local oil company,
but I don't know if they knew the outside-air intake was homegrown or
I did not understand before that you damper was that type. If your power
vent is pulling a lot of air in excess of what the furnace needs it would
seem that reducing the venting would solve the problem. It may not be
reasonably practical to do that. Outside combustion air would still reduce
the total amount of heated air lost. You might try to estimate how much air
enters the furnace compared to how much enters the damper. I suspect it may
be a minor loss compared to the cost of eliminating it.
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