Flush Mount Vent Screen Failure

Flush mount vent screen covers, sometimes referred to as surface mount and low-profile vent covers, are often used to terminate furnace intake and exhaust vents on the exterior of homes. Though aesthetically pleasing, these types of plastic vent covers are prone to screen failure which is often discovered only after the louvered screen breaks and allows a costly infiltration event to occur. On this page we will discuss why these flush mount vent screens fail, how to repair them and how to replace them with vent termination hubs and screen inserts to ensure the problem-free vent protection in the future.

Why Plastic Flush Mount Vent Screens Fail

Broke Flush Mount Vent Screen Louver

High efficiency furnaces, boilers and hot water heaters have condensing exhaust vents, which simply means there is moisture in the air being discharged. During sub-freezing temperatures, and throughout winter, some degree of icing is normal on exhaust vents. Unfortunately excessive icing can occur which causes the plastic louvers to come into contact with ice that expands and contracts. The expansion and contraction icing cycles, aided by the warm exhaust being discharged, may cause the louvered screen to crack and fail. Additionally, UV exposure also weakens plastic screens and louvers which also makes them brittle and more susceptible to failure. In the picture to the left, we have photographed a failed flush mount vent screen. In the image you will also see exposed debris that a small bird was using to build a nest within the exhaust vent pipe. The picture may be clicked on to show a larger and more detailed image in a new tab.

Repairing Broken Flush Mount Vent Screens

To repair a flush mount vent screen, and its broken louvers, a new cover must be installed since the entire cover is a solid molded piece of plastic. Those that do replace the cover often find they must replace it repeatedly over time. Additionally, flush mount vent covers offer limited vent protection and do not prevent bees, wasps and other insects from nesting inside ventilation systems or within appliances. Considering the limited lifespan and protection these types of vent covers offer, and the known problem of cross contamination from the intake being located so close to the exhaust, replacing flush mount vent covers with standard termination hubs is often the preferred permanent solution.

Replacing Flush Mount Vent Covers With Vent Termination Hubs

Exhaust Vent Riser for Furnace

Most flush mount vent covers are simply attached with either four or eight screws. In the image of the failed screen above, the cover attaches with four screws and may be unscrewed to expose the backing plate. The four screws attaching the backing plate to the home may be unscrewed to remove the backing plate to expose the straight PVC pipe. A 22-1/2° elbow may be added to the intake and pointed straight down. Due to the close proximity of the exhaust to the intake, a riser (pictured right) should be used on the exhaust so the discharge is a full 12″ above the intake to prevent cross contamination. On the exhaust, a 90° hub x hub elbow may be added to the exhaust pipe exiting the home so that a 14″ length of pipe may be inserted into it to create the rise. Finally, another 90° hub x hub elbow may be used to point the exhaust vent straight out. Once a dry fit of the PVC fittings and pipe prove successful, they may be cement welded in place and allowed to cure. After the cement welded PVC pipe and fittings have cured, the screws used from the now removed flush mount vent cover may be inserted partially into the unused holes so the wall anchors can be pulled out. With the wall anchors removed, a good color-matched exterior silicone caulk may then be applied to fill these four small holes and wiped flush with a wet towel to make them nearly unnoticeable.

Vent Screen Inserts for Hubs

Having successfully completed the conversion from flush mount vent cover to standard termination hubs, both the intake and exhaust vent may now be independently protected with the appropriate PVS series screen insert (pictured left) for seasonal protection. During spring, summer and fall 2″, 3″ and 4″ PVS-IS series insect screen inserts may be used to guard vents from insects, including bees and wasps, and of course anything larger including birds and mice. In sub-freezing temperatures, and throughout winter, 90% airflow rated 2″, 3″ and 4″ PVS-RS series vent screen inserts should be used as they exceed NFPA airflow requirements for winter use in applications involving combustion.

While converting a failed/broken flush mount vent cover to standard termination hubs can be accomplished with some basic DIY skills and < $50 in material costs, for many it’s best to leave it to the HVAC professionals. HVAC companies will typically charge around $200 to complete the conversion, though can be much less if they are already on location servicing a lockout condition, performing an annual furnace maintenance inspection or even to service a different appliance. Therefore, it is best to request the HVAC technician perform the vent conversion while they are already on location to avoid the cost of a separate service call.

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