After a very windy day I found a shiny item in my yard which
I'm calling a "roof vent cap". I had a new roof installed
about 15 months ago, and I assume this was one I had seen
when I was watching the workmen.
I painted it, and with a few tools got on the roof to see
where it went. There are 7 or 8 roof vents having interior
diameters of about 2". There are 2 roof vents having
interior diameters of about 4". Both of these larger vents
are within 3 feet of each other. I mounted the just-painted
roof vent cap on one of the vents. I'm wondering if both of
these larger vents should have such a cap. If not, I'm
wondering if I selected the proper vent for my installation.
As near as I can tell, the purpose of the vent cap is to
keep rain and perhaps small leaves from going directly into
the vent, so I think both vents need a cap. But looking at
other houses in the neighborhood, I don't see vent caps on
the smaller size vents, and on only some of the larger size
(From where these are located, I believe they vent the water
heater, and the furnace - both natural gas burners.)
Enlightenment appreciated on vent usage and recommendations.
Former slayer of dragons; practice now limited to sacred
Here in Canada, we would call "chimney" any pipe
used to disperse hot gas/air upwards, and all other
pipes are "vents." Chimneys should be capped to keep
out rain and snow and in this part of the world need
squirrel cages to keep out small animals.
The only vent that matters appreciably here is the stack
vent for sewage gas. For 51 weeks of the year no one
notices it: but at least once every winter the wind and
temperature conditions combine to drive sewage gas
down to ground level rather than disperse it upwards.
I have long thought that the stack vent ought to be
capped with a ventilator wheel on ball bearings, so
that a breeze in any direction will spin it and draw
air out of the system. But the crew that reroofed a
couple of years ago said they had never seen this
sort of gadget. Any way, for 360 days of the year
the ordinary laws of atmospherics work well unaided.
The larger pipes exiting through the roof could be either combustion exhaust
for a gas water heater or for the dryer.
Can you get into the attic to see where these originate?
I don't think you would want rain coming down to the water heater flames or,
likewise, into the dryer vent. If rain gets into the sewer pipe, who cares?
As for cap absenxe on the smaller pipes, there's not much than can get down
a 2" pipe (or would want to do so).
One of them comes down to the side of the furnace, near to
the vents from the furnace. The other one comes down
directly into the top of the water heater. I do have a gas
clothes dryer nearby, but the only vent from it goes out
through a wall to the outside, at about 12" above the
ground. I had assumed this vent was only for the hot air
from the dryer tumbler, but perhaps combustion vapors exit
heater flames or,
pipe, who cares?
Excuse my ignorance; I didn't realize that those smaller
vents led into sewer pipes. Since there are 7 or 8 or more
of these smaller vents, but only 3 toilets, I believe some
of them come from wash basins, sinks, or shower drains.
Maybe that water just flows on to the sewer line - makes
sense now that I think about it.
Yeah, they connect to the sewer lines. They serve two purposes: One is a
source of air so that suction doesn't pull out the water in the drain trap
and two, the reverse, so that overpressure in the sewer line (?) doesn't
push stuff back into the sink.
Each appliance that has a drain should be connected, ultimately, to these
little pipes. It's possible to have two sinks or bathtubs share a pipe.
Yes. I don't burn wood in it any longer, however. I have
some ceramic logs and gas burns around them when I turn it
on. There is a separate chimney for the fireplace.
Your question suggests I may be missing something here.
On ground floor, one kitchen sink, one bathroom sink, one
On second floor, two toilets, two bathroom sinks, two
Each of the three bathrooms also has a blower which exhausts
through the ceiling, perhaps having a separate roof vent for
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