Chimney guides

Unlined Chimneys in Massachusetts: Is Yours Safe?

Flue tile did not become standard practice until well into the twentieth century. On a Massachusetts house older than that, there is a good chance the flue is brick and mortar joints and nothing else.

The inside of an unlined brick flue seen on a camera survey

Short answer

An unlined chimney is not automatically unsafe, and a great many are still in service. What matters is the condition of the brickwork and mortar joints inside the flue, and what vents into it. After two centuries those joints have frequently washed out, which lets combustion gases into the chimney structure and sometimes into the house. Only a camera survey can tell you which case you have.

What the liner is for

A flue liner does three jobs, and understanding them is how you judge whether an unlined flue is acceptable.

Containing combustion gases

Keeping them inside the flue and out of the masonry and the building. This is the safety function and it is the one that fails when mortar joints wash out.

Protecting the masonry

Combustion products, especially from oil and gas, are acidic. A liner keeps them off the brick.

Giving the appliance the right size

A liner sized to the appliance makes it draft correctly. An open masonry flue is frequently far too large for a modern appliance, which is a combustion problem as much as a masonry one.

When an unlined flue is still fine

This is not a universal condemnation, and honest companies say so.

An open fireplace burning wood occasionally

The classic case for a serviceable unlined flue. Mortar joints intact on camera, no gaps, generous flue area for an open fire. Plenty of these are in use and there is no requirement to line them.

What changes it

Any change of appliance. Putting a wood stove or a gas insert into that fireplace means the flue is now wildly oversized for the appliance, and a correctly sized liner becomes part of the installation rather than an upgrade.

What rules it out

Washed-out mortar joints, gaps you can see daylight or adjacent flue through, spalling inside the flue, or any evidence that gases have been reaching the structure. Those are relining findings.

The options if it does need lining

Two, and they suit different chimneys.

Stainless liner

A flexible or rigid stainless liner fed down the flue and sized to the appliance, insulated where the chimney runs cold. This is the normal answer and it is the cheaper one.

Cast-in-place

A lining poured in place to form a new flue inside the old one. It costs more and takes longer, and it adds structural strength to the chimney — which on a badly deteriorated old stack is sometimes exactly what is wanted, because stainless alone does nothing for the masonry.

Need this done?

Chimney Relining across Massachusetts

Free to use, no obligation — we never charge you.

See chimney relining →

Frequently asked questions

Does an unlined chimney have to be lined by law?

Not retroactively in general. Requirements attach to new work and changes of appliance rather than to existing installations. The practical driver is usually a property sale or an appliance change.

Will my insurer care?

Some ask, particularly after a claim. A current Level 2 inspection report is the document that answers the question, which is a reason to have one on file.

Can I line it myself?

The material is available and it is a physically straightforward job on a straight flue. Sizing it correctly, insulating where required and terminating it properly are where it goes wrong, and warranties almost all require professional installation.