Unprotected and improperly protected boiler, furnace and hot water heater vents are the largest point of entry for outdoor pests to gain access into homes. For over a decade we have been guarding Class IV high efficiency appliance intake and exhaust vents from bees, wasps, birds, mice, chipmunks and more. We achieve full all-season vent protection by utilizing a 70% airflow rated insect screen during spring, summer and early fall when insects are active. During winter, our NFPA compliant 90% airflow rated rodent screens offer a professional grade solution that leading HVAC and plumbing companies across the nation trust to guard their customer’s vents in the coldest temperatures. The vent screens we manufacture are available for purchase in our online store.

Spring, Summer and Fall

When temperatures are warm, and insects are active, both 70% CVC-I and PVS-IS series vent screens should be used to guard intake and/or exhaust vents to prevent bees and wasps from entering ventilation systems. It’s quite common to see abandoned nests inside ventilation pipes when they are scoped with a camera. Each abandoned nest creates a restriction and over a period of years these nests can accumulate and result in the appliance failing to operate. Worse yet, yellow jackets can nest within furnace cabinets and gain access into the living spaces of homes. CVC-I and PVS-IS series vent screens are made with premium 18×18 mesh 316 stainless steel screens to provide years of trouble-free use.

Winter

In sub-freezing temperatures, and throughout winter, only 90% airflow rated CVC-R and PVS-RS vent screens should be used to guard Class IV boiler, furnace and hot water heater vents. Both CVC-R and PVS-RS vent screens meet NFPA standards for use in sub-freezing temperatures. The NFPA (National Fire Protection Association) is the standard setting organization that many states and municipalities in the United States rely on for their local building codes. Those who reside in regions that experience sub-freezing temperatures, and do not wish to change screens for insect protection during the warm seasons, should only use CVC-R and PVS-RS series vent screens.

Class IV high efficiency boilers, furnaces and hot water heaters have condensing exhaust vents which means there is moisture in the air being discharged. During winter this moisture can collect on screens, which is why we recommend using only our 90% airflow rated screens. With a 90% airflow rated screen, the surface area where moist discharge can collect and freeze is limited to just 10% and is easily melted during the next heat cycle. Additionally, CVC-R and PVS-RS series vent screens are made with lightweight and corrosion resistant 6061T6 aluminum housings that have been machined to precision tolerances. 6061T6 aluminum has excellent thermal conductivity to absorb heat from operating exhaust vents ten times faster than steel and nearly one-thousand times faster than PVC. During winter, the warm exhaust transfers heat to the aluminum housing which helps to prevent icing even in sub-zero temperatures. Since plastic acts as an insulator, and enhances icing during winter, we do not recommend using any vent screen made with a plastic mesh screen and/or housing as they are known to quickly accumulate ice and are prone to safety lockouts.

Changing Vent Screens for Seasonal Use

Those who reside in warmer regions that do not experience sub-freezing temperatures may use CVC-I and PVS-IS series vent screens year-round. Those who reside in regions that experience four seasons should use CVC-I and PVS-IS series vent screens in spring, summer and early fall until the first hard frost reduces the insect population. After the first hard frost occurs, CVC-I and PVS-IS series vent screens should be removed and replaced with their 90% rated CVC-R and PVS-RS counterparts in preparation for winter. CVC-R and PVS-RS series vent screens may be used throughout winter until spring arrives and long-range weather forecasts indicate freezing temperatures will not occur. All-season single and dual vent screen kits are available in our store.

General Information for Consumers

Since a byproduct of natural gas and propane combustion is carbon monoxide, we recommend reviewing the EPA indoor air quality page. Additionally, those who think a highly restrictive vent screen is needed to guard against mice should read the Fairfax County Health Department’s controlling rats and mice brochure (PDF opens in new window). While the Fairfax County Health Department notes mice can squeeze through an opening the size of a nickel (.836″ ⌀), other industry experts prefer to use a dime (.704″ ⌀) as a gauge for consumers. Regardless, the smaller dime is too large to fit through the .478″ openings of our NFPA compliant 90% airflow rated CVC-R and PVS-RS series rodent vent screens.

Those who have reviewed this best practices page, and still have additional questions regarding proper use, please use our contact form. For sizing questions, please review our vent screen sizing page.