Flue Liner Types & Installation Flashcards

Which factor most directly determines whether a round or oval flexible liner should be used in a relining project?

Answer: The shape and dimensions of the existing flue opening

The shape of the existing flue opening dictates liner shape; oval liners are used in flues too narrow for an equivalently sized round liner.

What is the main disadvantage of using a smaller-diameter liner than the appliance manufacturer specifies?

Answer: Insufficient draft can cause backdrafting and CO spillage

An undersized liner creates excessive flue resistance, reducing draft and risking backdrafting that allows CO-laden gases to enter the living space.

During a video inspection, a sweep observes that clay tile liner sections are no longer aligned and have shifted laterally. This condition is called:

Answer: Offset separation

Lateral misalignment of liner sections is called offset separation, which creates ledges that trap creosote and gaps that allow flue gas bypass.

A gas appliance is being downsized from a 120,000 BTU unit to a 60,000 BTU unit in a home. What liner concern should the sweep raise?

Answer: The existing liner may now be oversized, increasing condensation risk

A significantly oversized flue for a smaller appliance produces lower flue gas temperatures and velocities, increasing moisture condensation and reducing draft.

When installing a flexible liner down from the top of the chimney, what technique helps prevent the liner from kinking at bends?

Answer: Using a stiff inner guide rod or nose cone attached to the leading end

A nose cone or guide attached to the leading end of the liner helps it navigate offsets and reduces the risk of kinking during top-down installation.

What is the significance of a liner's 'continuous length' rating on a UL listing?

Answer: It indicates the maximum unjointed run length tested to the listing standard

The continuous length rating reflects the maximum unjointed liner length evaluated during listing tests, ensuring the listed performance applies to the installation.

Which liner installation scenario requires a separate combustion air supply to the appliance space?

Answer: When the appliance is in a tightly sealed or pressure-neutral space with insufficient infiltration air

Tightly sealed spaces lack sufficient infiltration air for proper combustion, requiring a dedicated combustion air supply to prevent backdrafting and CO production.