New chimney liners measured and fitted in Lake Mann Estates

Gas appliance flues follow their own rules

Section R1003.11.3 sends flue lining systems for gas appliances to the code's fuel gas chapter, and liner makers refer gas sizing to NFPA 54 and the appliance manufacturer. A liner sized by fireplace rules can be wrong for a furnace or water heater sharing the chimney.

When a gas appliance vents into your chimney, we size and specify that flue by its own rules and cite the reference in the estimate, so anyone who reads it can check the sizing. If the gas appliance is due for replacement, we suggest settling that first, since the new unit's manual may call for something different.

Clearance for a chimney outside the walls

For a chimney built entirely outside the structure, one liner maker lists 1 inch of unobstructed airspace to combustible materials in the United States, compared with 2 inches for a chimney inside the house. Siding, trim and framing near the chimney are part of that check.

The measured clearances decide whether the listed liner can be installed plain or needs its insulation wrap, and we show you which applies. If trim or siding has been pushed tight against the masonry over the years, we point it out even when it is outside the relining scope.

Questions worth asking before you approve relining

A sound relining proposal should answer each of these clearly. If one of them gets a vague answer, ask again, since each one affects how the liner performs or what the job includes.

• What finding makes the current lining unsuitable?
• Which listed product is proposed, and at what size?
• Is insulation required, or only recommended?
• What preparation happens before the liner goes in?
• Which old parts stay, and which come out?
• Which separate repairs, if any, are recommended?

When a liner cap has come off

A missing liner cap leaves the flue open to rain, leaves and animals. Replacing it with the cap listed for that liner restores the system, as long as the liner and plate below are sound.

We check those parts before fitting a new cap, and quote a replacement cap only when the rest of the top assembly can support it. If the old cap is lying on the roof or in the yard, leave it where it is. Its condition helps show why it came loose.