Main image upload

December 2015

Question

Can you provide advice on how best to deal with cracked chimney liners? My house was built about 15 years ago and has a concrete and clay flue chimney. I burn briquettes in a multifuel stove, but I have recently noticed sand falling down on top of this stove.

Do I need to install a stainless steel flexi liner or an insulated liner? Or do I need to have the chimney relined and rebuilt with modern methods?

Answer

Flue liners in a house built 15 years ago should not be causing trouble at this stage if using standard domestic solid fuel. It may well be an issue of poor workmanship during construction and the builder may have used dry sand as a backing to the flue liners.

Some fireplaces and flues were originally installed for use with gas fires only. Fireplaces installed for use with solid fuel must have heat expansion joints to allow for expansion and contraction.

You will need to organise a camera (CCTV) survey on the flue to establish if the liners are cracked or displaced and the extent of the problem. Have the flue swept ahead of this investigation work.

Check that the size of the current flue liners are suitable and sufficiently sized to facilitate a lining. If the house is only 15 years old, the flue is likely to comprise 200mm (8in) flue liners and may be suitable for lining with an appropriate stainless steel flexi liner.

However, this will reduce the diameter of the flue, thereby affecting the draw on the stove. A diameter of 150mm (6in) is the minimum recommended for a closed appliance up to 20kW-rated output burning coal, peat or seasoned timber.

If the liners are cracked or slightly displaced, then it is possible to line the inside of the flue with a suitable fire cement product repair system.

The worst case scenario is that the badly damaged flues will have to be taken out and rebuilt. This is done from within the room and involves removing blocks in sections and rebuilding the flue, stepping up the chimney breast and opening small sections as you go.

It may even be necessary to do a combination of both relining and rebuilding depending on the condition.

It is important that a liner is maintained in good condition to protect the house from heat transfer and protect the blockwork chimney from the corrosive by-products of combustion.

In addition liners provide a correctly sized flue for optimum efficiency of the stove appliance being vented.

Pat McGovern is a Chartered Building Surveyor and a member of the Society of Chartered Surveyors Ireland.