Frequently Asked Questions | SHL Distributors

FAQ – Frequently Asked Questions


Why insulate a flue?

There is no doubt that an insulated liner makes your masonry chimney preform and draught better than an uninsulated one – but when should a chimney be insulated or not?

The main reason to insulate your chimney liner is to ensure that it warms up faster than a liner without (Less heat loss from the exposed metal liner inside the masonry chimney).

When a flue liner is warmer, the flue gases inside the flue remain warmer for longer and rise more rapidly – this upwards movement aids the burning of the fuel inside your stove which means more heat in the room for you!

In addition, a hot burning stove aided by a correctly draughting chimney will mean;

  • Less sooty or creosote deposits collecting on the inside walls of the flue – these can potentially ignite and cause a chimney fire.
  • Less particulate emissions being released into the atmosphere which can be hazardous to human health.
  • The stove or fireplace will be less susceptible to wind forcing the fumes and gases down the chimney and causing a down draught.
  • The chimney will less likely suffer from cold air sinking down through it after the stove or fireplace has gone out.
  • The chimney is unlikely to suffer from a lack or draught where the fumes cannot escape upwards during combustion.

When is it necessary to insulate a chimney?

  1. If the chimney shaft is very wide, for example, 45cm x 45cm or more, there will be a large cold air void around the flue contained in the masonry chimney. This cold space will take heat from the flue liner if not insulated and may cause the chimney to draught incorrectly.
  2. If the chimney breast is proud of the wall and surrounded by cold air on three sides it is important to insulate the flue
  3. If the flue is contained in a long free standing chimney stack surrounded by cold air on four sides.
  4. If your chimney is short. Shorter chimneys do not draught as well as longer chimneys, therefore, it is advisable to help improve the draught in a short chimney.

What can be used to insulate a flue?

  • An insulating blanket or wrap such as AGC Thermal Wrap which is slipped over the flue as it is being installed.
  • Vermiculite or Perlite granules which are poured around the flue liner – beware of old chimneys which may have holes or have become porous – the granules may flow out into another flue or section / room of the dwelling. 

What are the most popular chimney cowls?

There are a variety of chimney cowls available for purchase on the Irish markets.

If one analyses the type and quantity of chimney cowl products available, one will see almost immediately which are the most popular, whether produced from stainless steel or inferior materials such as aluminium or mild / galvanised steel.

The most popular chimney cowl on the market today is that which prevents rain (and birds) from entering the chimney. In the UK, such chimney cowls are called Bird Guards and in Ireland, they are called Anti Bird / Anti Rain Chimney Cowls – the reason for this type’s popularity is the weather we experience in Ireland . Rain is almost a daily occurrence, and it is not uncommon to experience the four seasons in just one day!

The second most popular chimney cowl on the market today is that which prevents a downdraught – where the wind forces the fumes and / or smoke back down the chimney. Anti down draught chimney cowls are either stationary with no moving parts or a revolving chimney cowl that turns with the wind. Anti down draught chimney cowls are very popular because of the changeable wind patterns in Ireland – we get strong North Atlantic weather systems affecting us all year round meaning downdraught problems are very prevalent.

What is a down draught?

A down draught is also known as a back draught, blowback or sometimes just wind penetration

A down draught is defined as where the wind penetrates the chimney forcing the smoke and fumes down through the chimney and out from the fireplace or stove.

There are various causes of down draught including:

  • Wind moving downwards and into the chimney.
  • Wind moving across an obstacle such as a taller roof, building, trees / hedges or across a hill or mountain (especially if the dwelling is situated in a valley or depression). When the wind reaches the end of the obstacle, it will veer downwards and if the chimney is lower than the obstacle, the wind will then flow into the chimney.
  • If the chimney is situated on the windward side of the dwelling and a window or vent is open on the leeward side of the dwelling, the wind will flow down and through your chimney and out the window on the other side.
  • The fireplace or stove is more likely to be affected by a downdraught if there is no bend in the chimney.
  • The fireplace or stove is more likely to be affected by a down draught if the chimney suffers from a lack of draught.

Symptoms of a down draught include:

  • Smoke puffs intermittently out from the fireplace or stove when it is windy outside.
  • Soot gets blown down the chimney when a fire is not lighting.
  • Noticeable movement of the flame (especially when burning oil or gas). Sometimes but not often, the fire can be extinguished.

To solve a down draught you will have to fit an anti-down draught chimney cowl such as a Spinner Anti-Down Draught Chimney Cowl, Static Anti-Down Draught Chimney Cowl or H Anti-Down Draught Chimney Cowl. Read about each product carefully to decide which one suits your circumstances.

What is a lack of draught?

A lack of draught can be described as a lazy chimney, fireplace or stove or underperforming chimney. It can sometimes be confused with a down draught as the symptoms are very similar.

A lack of draught is defined as not having enough or inadequate draught or upwards movement of air, fumes and smoke through a chimney.

There can be many different causes of a lack of draught, they include:

  • Air tightness of the room or dwelling where the fireplace or stove is situated. This air tightness can be the result of double-glazed windows, wall, ceiling or roof insulation, draught excluders around and under doors, no vent installed in the room where the stove or fireplace is situated.
  • A short chimney – longer chimneys draught better than shorter chimneys.
  • A chimney without a bend – a bend in the correct place in the chimney can aid draught.
  • An incorrectly sized liner in comparison to the size of the fireplace or stove. The liner must be the correct diameter for the stove or fireplace it is serving. There is a specific ratio of 1 : 6.67 that this relationship depends on.
  • If there is an extractor fan or another stove or fireplace competing for the same volume of air the original stove or fireplace is using.
  • If the chimney liner is damaged or punctured the flue will suffer pressure loss.
  • If two stoves / heat producing appliance are connected to the same flue – this is not permitted under Irish building regulations and will adversely impact draught.
  • A blockage in the chimney can cause a lack of draught, to prevent birds from nesting please click here to read about the Anti Bird / Anti Rain Chimney Cowl.
  • If the throat of the fireplace is incorrectly formed or if there is no flue gatherer installed above the fireplace.

Symptoms of a lack of draught include:

  • Like a down draught, smoke can puff out from the fireplace or stove.
  • Smoke does not rise-up the chimney. This may occur on start-up or when the heating appliance and flue begins to cool down.
  • If there is a smell of soot the following day the stove or fireplace has been used.
  • If soot is found on the hearth or inside the stove the following day.

To solve a lack of draught and provided there is no blockage or structural problem (as described previously), an electrical cowl can be installed with a dedicated wall vent to the outside in the room where the heat producing appliance is situated to increase draught. Click here to read about the Super C Electric Fan Chimney Cowl. For a more powerful solution than the Super C, click here to read about the Super R Electric Fan Cowl.

Occasionally, a chimney must be relined, un-blocked or rebuilt. A relining should be carried out by an experienced chimney specialist. We sell all the materials used to reline a chimney, click here to read about flexible chimney liner.

How do I stop rain getting in my chimney?

Excessive rainwater penetrating the chimney can possibly cause damage to the chimney, fireplace or stove. Worse again, if left for a long time, dampness can penetrate the fabric of your building’s structure.

There are many causes of this problem, including:

  • Straight chimney where the water can drip or flow directly into the fireplace or stove.
  • Large opening at top of stack – prevalent in older properties where there is no chimney lining and therefore the chimney stack has a larger square or rectangular opening where a chimney pot would normally be situated. The bigger the opening at the top of the stack, the greater the volume of water that can get in.
  • No anti bird / anti rain chimney cowl fitted to the chimney pot.
  • The flashing around the chimney stack is leaking allowing water to penetrate.
  • If the plaster on the walls or the cladding of the chimney stack is cracked from for example a chimney fire, old age, or subsidence, again, water can penetrate.
  • The concrete chimney capping has cracked, perhaps from a chimney fire.

Symptoms of rainwater damage include:

  • Water dripping into the fireplace.
  • Water dripping into the stove and causing the inside of the stove to rust.
  • Water dripping onto the top of the stove and causing the top of the stove to rust.
  • Dampness in walls close to or below the chimney stack
  • Blackness discolouring the walls close to or below the chimney stack.
  • Tar in the chimney and possibly tar dripping down the chimney into the fireplace or into / onto the stove.
  • Deterioration of the fabric of the chimney shaft
  • Deterioration of masonry work outside the chimney

To solve rainwater ingress, it is important to first identify where the water is getting in. If there is deterioration of the chimney stack including plaster, capping or flashing it will be necessary to get a chimney specialist or roofer / mason involved to carry out the remedial work. If water is getting through the chimney pot, we suggest you install either an Anti-Bird Anti Rain Chimney Cowl or Static Anti Down Draught Chimney Cowl.

What is excessive draught?

Excessive draught is when you have too much draught or air going up your chimney. It can also be described as an over performing chimney or flue.

What is an up / down problem?


How do I stop birds nesting in my chimney?

This problem usually occurs in a chimney that is not used very often or when there is no chimney cowl installed.

When birds nest in your chimney you may notice the following:

  • You have a blocked or partially chimney.
  • The smoke from your stove, fireplace or insert is not escaping up the chimney.
  • You suffer from a chimney fire when the nesting material ignites.
  • Bird or animal activity in and around the chimney stack area.
  • Bird noises inside your chimney.

To solve this chimney problem, you should sweep the chimney after Spring / Summer when nesting has finished and install a chimney cowl such as the SHL Anti Bird / Anti Rain Chimney Cowl. This will stop birds from nesting inside your flue.

How do I care for my newly installed solid fuel stove?

When you light the stove for the first time, you will notice an acrid smell. This is normal. The paint and fire cement needs to cure, and this will take 4-6 fires. We suggest lighting small fires and gradually build them bigger over time until the smell fades.

If using a multi fuel stove, we recommend a fuel mix of 60% kiln dried timber (with a moisture content of 20% or less) and 40% coal. Timber gives a great flame and heat, smokeless coal gives you extra burn time. This mix percentage will ensure that your grate lasts longer than if you burn just coal.

We recommend that the chimney is cleaned with nylon brushes bi-annually for moderate to heavy stove use (4-7 days a week) and annually for light to moderate use (0-4 days a week)

We also recommend that the rope seals/gasket around the door and glass are changed annually – this will ensure you have ongoing full air control.

Paint by its nature will fade over time, especially if it is exposed to the type of temperatures that a stove can generate. You may want to respray your stove 1-2 years after purchase.

We recommend the following after-care products:

  • Stove glass cleaner – use every time before you light the stove to clean the glass.
  • Flue free creosote cleaner – this prevents build-up of creosote on your flue which is difficult for a chimney sweep to remove. Creosote can catch fire relatively easily. Burning moisture rich fuels such as turf and damp timber will cause its build-up. Use creosote cleaner once a month.
  • Slate oil– keeps your stone hearth a lovely deep dark colour. Use slate oil as often as you need to maintain colour.
  • Fibreglass rope and a tube of high temperature glue should be used to replace rope seals and gaskets around doors and glass.
  • High temperature stove paint comes in a spray tin and is used to respray your stove. Ensure stove is wire brushed and clean first before using.

These products can be bought from any good stove shop,  builder provider or hardware store.

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