Roof Vent Cap Question

[CWLee]

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 vents.

(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.

Thanks.

[Don Phillipson]

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.

[HeyBub]

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).

[CWLee]

"HeyBub" wrote

combustion exhaust

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 there also.

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.

Thanks.

[Art]

Do you have a fireplace?

[HeyBub]

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.

[CWLee]

"Art" wrote

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.

Thanks.

[mm]

Wow! How many sinks and toilets do you have?

One story house, right?

[CWLee]

"mm" wrote

On ground floor, one kitchen sink, one bathroom sink, one toilet. On second floor, two toilets, two bathroom sinks, two showers. Each of the three bathrooms also has a blower which exhausts through the ceiling, perhaps having a separate roof vent for each.

No, two.

Next question? :-)

[dcbritt]

responding to

dcbritt wrote: You can purchase a PVC vent cap from Each cap is less then $10 and easy to install. By far the best solution to keep debris and critters out.

[dcbritt]

responding to

dcbritt wrote: You can purchase a PVC vent cap from Each cap is less then $10 and easy to install. By far the best solution to keep debris and critters out.