I am considering tacking wire mesh (such as from a window screen) onto the inside of my indoor furnace/AC duct vents as well as the outdoor intake vents, for pest control. I know doing it inside the house might be a little overkill, but I'm wondering if there would be any side effects on furnace/AC performance due to the fans having to work harder to force the air through.
Vent – Side Effects of Wire Mesh Inside Vent Covers
ductsfurnacevent
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IANAP (I Am Not A Plumber) but I have recently replaced my old cast iron stack.
The relevant part of the International Plumbing Code looks like section 904. Specifically the following sections may apply to you.
904.1 Roof extension. All open vent pipes that extend through a roof shall be terminated at least [NUMBER] inches (mm) above the roof, except that where a roof is to be used for any purpose other than weather protection, the vent extensions shall be run at least 7 feet (2134 mm) above the roof.
Note the [number] is usually specified by your local codes as it is very specific to each region. Some web searching turns up a few forum posts from plumbers in Ontario who say it needs to be 6 inches above the roof. That does not sound like much to me and if you are already at 6" and having issues it seems reasonable to go higher.
904.2 Frost closure. Where the 97.5-percent value for outside design temperature is 0°F (-18°C) or less, every vent extension through a roof or wall shall be a minimum of 3 inches (76 mm) in diameter. Any increase in the size of the vent shall be made inside the structure a minimum of 1 foot (305 mm) below the roof or inside the wall.
904.3 Flashings. The juncture of each vent pipe with the roof line shall be made water tight by an approved flashing.
904.7 Extension outside a structure. In climates where the 97.5-percent value for outside design temperature is less than 0°F (-18°C), vent pipes installed on the exterior of the structure shall be protected against freezing by insulation, heat or both.
I don't know the preferred method for doing this but if you plan is to add a coupling from inside the house and "push" the pipe up, I bet you will compromise the water tight seal around the pipe at the roof. The simplest solution would be to add this extension at the very top so you don't have to mess with the flashing at all.
If this is the main waste/vent stack for the home, I don't think you are allowed to reduce the diameter of the pipe (even up at the "vent" portion). I don't know if that is still true for smaller vents that service just a few fixtures.
If it is black plastic, it is ABS and should be easy to cut and glue.
My experience using those brushes is that it's difficult to tell if you're pushing on a lint blockage, a turn in the pipe, or your knocking the cap off the end of the pipe. So if at all possible, you should have the end open and/or connected to a vacuum. You don't want this tool ramming into the motor in your dryer, nor do you want it knocking the damper off the outside of your house. In your case, that's going to require someone on the roof.
You can get close, keeping track of how many segments of the cleaning tool you used to get to the roof in a previous cleaning, and then stop a few feet early. But as Michael says, the cap itself should be cleaned since lots of lint will build up there.
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Typical screening can reduce airflow about 50 to 70%. This could destroy the efficiency of your AC and heating units and possibly burn out the fan. Placing any type of screen on intake or exhaust of your furnace could cause it to shut down as it thinks there is a blockage in the venting. Your furnace /AC unit already has a filter on the intake side of the fan so you wouldn't need screening on the individual vents in the rooms.