If you drive through any neighborhood in Minneapolis or Saint Paul, you'll find a handful of gas vents with missing or improper vent caps. These improper caps all need to go.
The most serious problem with this style of vent cap is that it can collapse and block the vent.
The condition pictured above is an imminent safety hazard that needs immediate repair; this will likely cause the combustion gases from the furnace and water heater to backdraft into the home. Not only that, but this will also cause the combustion appliances to burn improperly, causing high levels of carbon monoxide to enter the home. That's how people die. Again, this is extremely dangerous.
What to do about old vent caps
The simple fix for this condition is to replace the vent cap with a new, UL listed vent cap. Just stop by any home improvement store and you'll find them in the HVAC department. If you look for these in the roofing section, you probably won't find the right one.
Newer vent caps will be somewhat enclosed at the top, which will help to prevent water and pest intrusion. This design also helps to prevent wind from causing gas appliances to backdraft. Also, these designs won't allow the cap to collapse and block the vent.
The one that I'm blogging about today was commonly known in the trades as a "coolie cap".
"Coolie" is a dated, offensive term for unskilled Asian workers that shouldn't be used. A few PC terms for this cap would be an "unlisted cap", an "unapproved cap", or a "witches cap".