Due to the similarity in appearance of concentric (conical or cone shaped) vents and exhaust vent accelerators, consumers may be compelled to incorrectly purchase a concentric vent screen for their boiler, furnace or hot water heater. To eliminate any confusion, this page has been designed to help our customers properly identify the presence of an exhaust vent accelerator so they may select the correct vent termination screen.

The Purpose of an Exhaust Vent Accelerator

The exhaust discharged from high efficiency boilers, furnaces and hot water heaters is mildly acidic. Moving the exhaust further away from the home and surrounding objects can be beneficial as the acidic exhaust may accelerate corrosion on nearby objects including steel doors, windows, exterior plumbing, and air conditioning units. By utilizing a simple PVC reducer coupling, to reduce the inside diameter of the exhaust discharge point, increased discharge flow velocity is attained. By discharging the exhaust at a higher velocity, the acidic exhaust will be pushed further away from the home and nearby objects during heat calls.

Identifying Exhaust Vent Accelerators

As seen in the furnace exhaust vent accelerator pictured below, the HVAC installer reduced a 3″ PVC vent pipe to 2″ at the termination. While concentric vents have an opening behind the cone, which is where the intake draws in fresh air, the pictured accelerator has been cement welded to the 3″ PVC pipe with no opening in the rear. Unlike concentric vents, which often have large forward facing words “do not block intake” embossed on the cone, the outer surface of this accelerator is smooth and without any visible identification marks.

Those with an exhaust vent accelerator installed for use on their high efficiency boiler, furnace or hot water heater can typically locate the sizing used on the reducer. For example, 4″ x 3″ will typically be embossed on the end of the reducer coupling whereas other manufacturers will emboss the sizing on the outside diameter. The same manufacturer sizing information applies for 3″ x 2″ reducers used to create a 2″ vent termination.

Guarding an Exhaust Vent Accelerator Termination with a Screen

Since standard PVC reducer couplings are used to increase the discharge flow velocity on boiler, furnace and hot water heater exhaust terminations, our PVS series vent screen inserts may be used to protect this type of vent. As pictured to the left, the reducer coupling has an inner flange where our PVS series vent screens will seat against when installed inside the termination. Especially with this style of termination, screen inserts are preferred as the coupling shields the screen from exposure to debris and precipitation while also positioning the installed screen closer to the heat source.

To determine the correct PVS series vent screen for your vent, please measure the vent’s opening (inside diameter) and compare your measurement to the dimensions found on our vent screen insert sizing page. It’s important to note PVS series vent screens may be purchased in discounted all-season kits in our store.

Prevalence of Exhaust Vent Accelerators and Other Considerations

Unless there is a clear reason to utilize a reducer to increase the discharge exhaust flow velocity for a boiler, furnace or hot water heater, the use of an accelerator is generally considered old school and avoided by most HVAC and plumbing technicians. These days, any size reduction in an exhaust vent’s termination is considered an unnecessary restriction to be avoided. In most cases, HVAC and plumbing installers will terminate the exhaust vent in a location which does not require an accelerator unless the appliance manufacturer specifies otherwise.