Venting Issues For Replacement Furnaces

Standard B-Vent Exhaust

When a replacement furnace is to be installed, an important factor to consider is whether or not your existing gas hot water heater needs to be re-vented.

If the existing furnace shares the same b-vent exhaust as the natural draft gas water heater, you may have to do that. The reason is that now only a single gas appliance is using the vent designed for two appliances to share. This results in a pipe diameter too large for the single appliance, therefore the water heater's hot exhaust gas will dilute too much with the cooler air inside of the existing venting. The result is that the cooler exhaust gas may fall back down into your home, along with all of the very dangerous products of combustion - carbon monoxide, etc.

Vent With Rain Cap Removed

Re-venting can be as easy as installing a vent liner kit. The process starts, in most cases, by removing the rain cap from the end of the exhaust on your roof.

Vent Liner Being Inserted

With the rain cap removed, a 4" flexible liner is inserted into the existing 6" vent. This effectively reduces the venting from 6" to 4" - the proper size for venting only a water heater according to our local codes.

This liner saves the work of opening walls, etc., to install new venting from scratch and saves considerable costs on a new furnace installation.

The 4" Liner Entering the Furnace Room.

The 4" liner is drawn into the furnace room where it will be properly connected to the hot water heater.

It is important to note that gas codes vary by state and province. Therefore, you should always check with your local authority for proper codes for your area.