The construction and installation of a chimney for a fireplace

A chimney for a fireplace is quite a complex construction, and the correct working of the whole heating system, fire safety, the integrity of the house and even your life and health depend on choosing and installing it correctly. So the installation rules should not be neglected — and better still, this work should be entrusted to specialists straight away.

We have written before about what types of chimney there are and the main rules for choosing them. In this article we look in more detail at the construction of a chimney system and work out how to install a chimney for a fireplace correctly.

The construction of a chimney for a fireplace

In order to install a chimney correctly, you first need to understand what it consists of and what each of its elements is for.

construction of a chimney for a fireplace

What elements does a chimney consist of?

A chimney is not assembled from random pipes but from a set of standard parts, each of which performs its own function. All the elements listed below — pipes, elbows, tees, inspection doors, fixings and terminal parts — can be selected in the CHIMNEYS section, so that the whole run comes from one system and the parts fit together exactly.

The elements of a chimney and what they are for:

Single-wall chimney pipe. The basic element for making up and installing a chimney and its horizontal sections. Chimney pipes are used for lining a brick flue and also for connecting to a twin-wall insulated chimney. Supplied in lengths of 1 m, 0.5 m and 0.3 m.
45° elbow. Consists of two sections of pipe welded together at an angle of 45°. It allows the direction of the chimney to be changed by 45°. It is fitted on both vertical and horizontal sections of the flue. A 45° bend must not carry a load (the weight of the chimney) but should only perform the function of a turn.
Adjustable 90° elbow. Designed for changing the angle of the chimney; it joins to the stainless steel elements of the flue without additional fixings, pipe into pipe.
45° tee. Designed for leading the departing gases into the chimney; it provides the possibility of cleaning and servicing the flue pipe and of separating out condensate.
87° tee. Designed for leading the departing gases into the chimney; it provides the possibility of cleaning and servicing the flue pipe and of separating out condensate.
Inspection door. Intended for internal checking, servicing and cleaning soot out of the chimney, and it also acts as a support for the stainless steel flue pipe.
Condensate drain. Intended for draining condensate out of the flue pipe. The condensate drain is fitted at the bottom, under an 87° or 45° tee.
Damper. Intended for regulating the draught in the flue pipe. Under the fire regulations in force in Ukraine a damper must not close off more than 85% of the cross-section of the chimney.
Chimney terminal. Used for fitting on the top of a brick chimney. The terminal of a brick chimney prevents precipitation getting inside the brick flue.
Storm collar. Fitted to the flue pipe where it emerges onto the roof; it prevents precipitation entering the opening around the chimney and also finishes the passage of the pipe through the structure.
Trim plate. Intended for finishing the places where the chimney system passes through a vertical structure (a wall or partition).
Guy bracket. Fitted to insulated flues when the chimney pipe rises more than 1.5 m above the roof.
Fixing bracket. Intended for fixing the vertical stack and the horizontal sections of the chimney to the wall, where the distance from the pipe to the surface it is fixed to does not exceed 200 mm.
Cowl. Fitted to the top of the chimney and intended to increase and stabilise the draught. Cowls also protect the flue pipe from precipitation and strong side winds.
Rotating cowl. Fitted on top of the chimney; it protects the flue from precipitation and rules out the wind blowing down into the chimney (draught reversal).

The full list of these parts with their diameters and lengths is gathered in the catalogue in the chimneys section. It is more convenient to specify the run as a complete set at once: that way you will not have to search for adapters between parts by different manufacturers. For prices of specific elements, please check with a manager or a representative in your region.

The flue pipe

The flue pipe is the basic element of the whole chimney system. In essence it is the device fitted at the top of the flue, intended to carry combustion products away into the atmosphere.

A flue pipe must meet the following requirements:

the flue pipe must have the same internal cross-section and shape as the chimney;
the flue pipe must have an effective outlet cross-section no less than twice that of the chimney;
the part of the pipe that emerges from the roof or remains in contact with the space outside the building (in the case of a flat roof, for example) must be enclosed in brick or tile and in any case well insulated;
the flue pipe must be built in such a way as to prevent rain, snow and foreign matter getting into the chimney, and to ensure that combustion products are carried out into the open air in the case of winds blowing from all sides and at all angles (a pipe with a downdraught cowl).

Installing a chimney for a fireplace

Before starting the installation of a fireplace chimney, preparatory work should be done. That allows the most effective, safe and practical system to be built, with a long service life.

To begin with, the insert of your fireplace must be installed; and if special legs are not provided, a fire-resistant support will have to be built. There must be thermal insulation next to the wall adjoining the fireplace. Specialists advise using mineral wool for this, which withstands large temperature swings, up to 700 degrees.

What distance should be left between the insert and the wall?

This is a parameter that must not be taken "out of your head" or from somebody else's advice. The minimum distances from the insert to the walls and neighbouring structures are set by the manufacturer in the data sheet of the specific model — those are the figures that are binding, because they depend on the construction of the body, the output and the way the air is supplied.

! THIS IS IMPORTANT !

TO COMBUSTIBLE STRUCTURES (TIMBER, PLASTERBOARD ON A TIMBER FRAME, INSULATION, FURNITURE) — NO LESS THAN 10 CM, AND INSULATION IS MANDATORY

So the order is as follows: first we look at the data sheet for the model and comply with the manufacturer's requirement; if there are combustible materials nearby, the distance to them must be no less than 10 cm, and thermal insulation must be provided between the insert and such a structure. The data-sheet distances for a specific model are given in the product characteristics — look at straight steel inserts, corner inserts or fireplace stoves, and if necessary agree the enclosure design with a manager.

The installation of a chimney for a fireplace can only begin once you have placed the insert in the position carefully chosen for it.

! THIS IS IMPORTANT !

MORE THAN ONE APPLIANCE MUST NOT BE CONNECTED TO A SINGLE FLUE

The next stage is setting the slope and determining the axis of the outlet from the smoke collector, which must coincide 100% with the axis of the smoke removal.

The joints inside the chimney are treated with a double layer of sealant, and after that the assembly of the construction can begin.

! THIS IS IMPORTANT !

Work on erecting the chimney should begin only when the insert has been installed in the optimum position and the rules listed above have been observed.

The chimney is installed from the bottom upwards. The part that is located inside must be inserted into the preceding element of the system, while parts of the external section are fitted over the top of the preceding one. The principle of such an arrangement prevents condensate reaching the insulation inside the outer casing.

Chimney pipes are secured with clamps and the joints are covered with aluminium tape. The lengths of pipe must be calculated so that the fixing clamps do not fall at the points where the flue passes through floors. An additional layer of insulation should be placed at the joints, in order to avoid excessive heating of the outer casing. When fixing flue pipes to the wall it is necessary to make sure there are no misalignments or sags. Contact with any other utility systems or with the roof structure must not be allowed.

While still at the purchasing stage it is worth counting how many parts, and which, your particular run will need: straight lengths, elbows, a tee with an inspection door, a condensate drain, fixing brackets and the terminal element. All of that is in the chimneys section, and the accessories for looking after the fireplace will help to close off the flue during cleaning.

! THIS IS IMPORTANT !

A correctly designed, correctly installed and promptly serviced chimney is the foundation of stable and efficient operation of a solid-fuel appliance.

Please note! The advice given in this article will help you to install a chimney for a fireplace yourself, but of course, before starting the work it is worth consulting specialists, or even ordering the appropriate service from a firm that installs chimneys.

The rules for using a fireplace chimney

It is important not only to choose and install the chimney correctly but to use it properly. Certain requirements must be observed when operating a chimney.

When lighting the insert you must not use liquid firelighters or other easily flammable substances.
For solid-fuel fireplaces you must not use firewood larger than the dimensions of the firebox.
Clearing soot from the chimney by burning it out can cause the premature failure of the chimney system.
A fire lit in the firebox must not be put out with water — the excess steam can cause an explosion, small though it may be, capable of substantially damaging or even destroying sections of the chimney.

How often should a chimney be cleaned and inspected?

Cleaning the chimney is an unavoidable and absolutely necessary process, since a fouled flue is the cause of a loss of draught and a fire risk.

Already at the design stage of the chimney, provision should be made for such elements as:

an ash collector with a door;
inspection hatches in the horizontal parts of the flue.

These elements are needed to monitor the condition of the inner surface of the chimney and to carry out its cleaning. How often cleaning is required depends on how quickly the flue is fouled by combustion products, and that in turn depends on such factors as:

the type and quality of the solid fuel;
the construction of the chimney (whether there is a layer of thermal insulation);
the operating regime of the insert (setting up the optimum combustion process).

Checking through the inspection hatches for fouling in the chimney is recommended no less often than once a month.

Cleaning the chimney can be carried out as it becomes fouled, but no less often than once per heating season.

When wood burns slowly, soot and steam are produced. The soot contains organic substances which react with the water vapour given off by the wood. As a result a creosote deposit forms on the walls of a cold chimney. If that deposit catches fire, a flame with a very high temperature will result. The build-up of creosote must be checked regularly in order to determine how frequently the flue needs sweeping. Remember that the more intense the burning, the less creosote is deposited.

The layer of soot on the walls of the chimney should be removed periodically, in order to avoid the risk of ignition. This can be done in two ways: mechanically, with special brushes, and by using various chemical preparations.

Mechanical cleaning of a chimney is carried out with a special cylindrical brush, which is fixed to a rod or rope and lowered into the flue from above. Sometimes specialists also use special vacuum units, with which soot is drawn out through the inspection door.
Chemical cleaning of a chimney is carried out with special preparations added to the firebox during the burning of fuel.

Whichever method you choose, such work is better entrusted to a professional. They will check the chimney thoroughly before cleaning and, if necessary, carry out a technical inspection of the flue. And thanks to the use of professional equipment and materials, you will be sure that your chimney is clean and safe.

A chimney fire

A fire in the chimney can arise as a result of irregular and infrequent cleaning, of burning wet or damp wood, and consequently of the ignition of creosote (an easily flammable substance released when wet wood is burnt).

The characteristic signs of a chimney fire are:

the smell of combustion products (soot) in the house;
suspicious noises in the chimney that were not heard before;
a sharp rise in the temperature of the flue;
the appearance of sparks or flame in the chimney.

In the event of discovering a chimney fire it is necessary to:

call the fire service immediately;
as far as possible put out the fire in the flue using sand or earth;
a chimney fire must not be put out with water, since the sudden cooling of the flue and the evaporation of the water can cause the chimney to split and the fire to spread;
cut off the air supply to the fireplace: close the firebox door and shut off the primary and, if possible, the secondary air.

After a chimney fire a specialist must inspect its technical condition. Only after that may a fire be lit in the fireplace again.

What should be taken into account before installing a chimney?

To sum up everything said above briefly: first the insert goes into its place, observing the data-sheet distances and the insulation; then the run is assembled from the bottom upwards out of parts from a single system; the joints are sealed and secured with clamps away from the zones where the flue passes through structures; an inspection door and a condensate drain are provided at the lowest point; and only one heating appliance is connected to a single flue. The components for this are gathered in the chimneys section, the heating appliances themselves in the fireplaces and stoves section, and day-to-day care of the system is simpler with the right accessories.

How safe is your chimney