Wood Stoves in the Berkshires: Why the Liner Matters

Why the flue size matters so much

An open fireplace needs a large flue because it is pulling a large volume of room air up the chimney. A stove is a sealed appliance pulling a fraction of that through a six-inch outlet.

Put the stove on the fireplace flue and the same amount of heat now has to warm several times as much masonry. The gases cool below the point where water vapor and wood tar stay in suspension, and they condense on the flue wall. That is creosote, and it accumulates fastest exactly where the flue is coldest — high up, where you cannot see it.

The draft problem is the same cause. A cool flue does not pull. That is why these installations smoke back when you open the door, are hard to light, and burn through wood without heating the room.

Insulated, not just smaller

An uninsulated liner in a cold exterior chimney still loses heat. Insulation — a wrap or a pour — is what keeps the gases hot enough to leave as gas. In an unheated Berkshire chimney it is not optional.

Sized from the stove

The diameter comes from the stove manufacturer, usually matching the flue collar. Bigger is not better and is in fact the whole problem.

Burning practice does the rest

A correct liner removes the structural cause. Two habits remove most of what is left.

Moisture content below twenty percent

Seasoned hardwood burns hot and clean. Unseasoned wood spends the fire's energy boiling water out of itself, running the fire cool and smoky and laying creosote down several times faster. A moisture meter costs very little. Wood that hisses or blackens the glass is not ready.

Do not damp it right down overnight

It feels economical and it is the most reliable way to coat a flue. Cool smoke condenses; hot smoke leaves.

Ask what stage the deposit was

After a sweep, ask whether it was stage one, two or three. That answer tells you whether your annual interval is right or whether you need a mid-season check.

When the power goes out

In the hill towns a stove is frequently the heat that still works in an outage, which makes it worth more than convenience and worth maintaining accordingly.

It also means the stove gets run hard for days at a stretch in exactly the conditions that produce creosote fastest — long burns, damped down, in the coldest weather of the year. A flue that is marginal in normal use is the one that has a fire during a storm.