90% Furnace Tip

Many HVAC contractors wonder why Rheem 90+ furnaces require going back down to two inch flue pipe when exiting the building. The main reason for this is to accelerate the flue gasses so they are not pulled back into the intake pipe, and to keep the gasses farther away from the building, decreasing the possibility of the gasses coming back in. Armstrong recommends what they call "accelerators" on their 90+ furnaces for the same reason. On Armstrong A96 and A97 models an accelerator (reducing the flue size) is required.