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Wood Burning Stove Problems

Advice about Wood Burning Stove ProblemsMinster Stoves & Heating offers competitively priced multi-fuel and wood-burning stove installation and stove servicing in Herefordshire, Worcestershire, Shropshire & the surrounding areas.

If you are having wood-burning stove problems, the information below may help, however, we strongly suggest that you have your stove serviced to ensure that it is safe to operate. Please contact us to arrange a service.

Smoky Starting

A smoky start happens when the stove is first lit, then after a few minutes begins to work properly. The following things should be considered:

  • Wood Burning Stove Dampers – Inside a wood-burning stove or in the pipe leaving the stove, generally you will find a damper. A damper consists of movable metal plates that help control the flow of smoke and gasses. The damper must be fully open, to allow maximum draft when you light the stove. The highest concentration of smoke is produced on first lighting. If a damper is left slightly or completely closed when lighting, the stove will most likely smoke.
  • Cold Flue when lighting – Warm air rises & cold air sinks – for a chimney to operate properly, the flue must be warm compared to the air surrounding it. A warm flue causes the smoke to rise up through the chimney & leave the room. If the flue is cold (can happen for various reasons but is more noticeable when the outside air is cold) when the fire is lit, smoke might be drawn back into the room. Once the flue begins to warm up, the chimney will start to “draw” & smoke will rise up the chimney. To prevent this, the flue should be primed prior to lighting the fire.
  • Blockages – Sometimes, a smoking problem can be caused by blockage of the flue. Creosote build-up, bird nests, leaves/debris, or internal collapse of the chimney lining or brickwork can all cause blockages. If you think your chimney may be blocked, make an appointment to have your chimney inspected/swept. Bird nests can be prevented by the fitting of a suitable cowl.
  • Ash – Don’t allow ashes to build up too high in your wood stove. They will eventually block the air intake from the draft registers. Leaving about an inch or so of ash is beneficial as it provides an extra layer of insulation between the bottom of the stove and the fire.
How to “prime” the flue

Roll up a couple of pieces of newspaper, light one end, and hold it in the firebox of the woodstove, up near the flue collar (where the flue is connected). You will soon feel the draft reverse, as the warm flue gasses start to move up the flue. Once you have primed the flue, you can light the fire. If this doesn’t solve the problem, leave the stove door open for half an hour or so, this will allow the warmer room air to permeate the flue.


Smoky Endings

If your stove seems to work well once you get it going, but smokes when the fire is going out, here are some possible causes:

  • External Flue System – Chimneys built on the outside of the house are notorious for smoking problems when the fire is burning low due to exterior cooling. Chimneys built up through the home are insulated by the surrounding building and are less susceptible. As the fire dies, less heat is produced to keep the flue warm & the draft weakens creating the potential for smoke spillage. This is usually a contributing factor, there are normally other issues: For wood stove venting systems, bigger is not better. An excessively large flue will require more heat to remain warm, and cools more quickly than a correctly-sized flue. Lower flue gas temperatures in large flues cause a reduced draft, increased creosote build-up (smoke tends to cool & condense in the flue), and the potential for smoking problems when the fire is not at full burn. Inadequate available air in the home can create smoking problems, especially as the fire burns low, reducing the heat vented into the chimney.
  • Multiple appliances are connected to the same flue. In years gone by, multiple appliances were often connected to the same flue i.e. a fireplace or other appliance. Newer standards require that a wood stove has its own separate flue. There are several good reasons for this:
  1. Soot & creosote from the wood stove could potentially block the flue, causing toxic exhaust from other appliances to enter the home.
  2. The draft to one appliance can be severely affected by the other appliance.
  3. Exhaust products, when combined, could react adversely.
  • No Chimney Cowl – A cowl helps deflect wind. Some are specially designed as downdraft-deflectors. If you don’t have a cowl, arrange to have one fitted. While a standard chimney cowl is not specifically designed to deflect wind, merely having a “lid” above the opening will help reduce some wind-related smoking problems. However, if downdraft problems are severe, a downdraft-deflector cowl might be a better option. This type of cowl has a baffling system that re-directs the wind or in some cases causes a slight increase in chimney draft as the wind hits the cowl.

Cracked, Broken or Cloudy Stove Glass

Under normal use, the stove glass will not crack or break. Glass breakage can be caused by:

  • Impact (hitting the glass with a log, or slamming the door into a protruding log)
  • Severe over-firing of the stove
  • Splashing cold liquids on hot glass
  • Improper glass installation

In the majority of stoves, glass is held in place by steel clips or cast-iron or steel frame. There is a gasket between the glass and the door, but not always between the glass and the clips or frame. If the frame is over-tightened or unevenly tightened, especially with doors that use clips, the glass could break from heat stress.

99% of modern stoves have an air wash system designed to keep the glass on your stove clean. However, should you burn unseasoned wood (below the critical 25% moisture content) on the stove or your chimney is unlined or is not generating sufficient draught for one reason or another you may find that this glass will cloud up. This can be cleaned with the specialist glass cleaner – ask us for a cleaning pack! Alternatively, you can try lemon juice mixed with wood ash. If the chimney is the issue please consult us and we’ll take a look.

The rope door seals need to be inspected regularly for wear and tear. We suggest these are replaced annually to ensure your stove is as efficient as possible. Worn door seals will contribute towards the dirty glass.


Creosote Build Up

Creosote is a product of incomplete combustion: comprising deposits of unburned, flammable tar vapours from wood smoke. Sometimes it is crusty or flaky in texture, but often sticky or hard. Creosote deposits are often hard to remove from chimneys and it is also extremely flammable and is responsible for many chimney-related structural house fires each year.

Creosote forms when the wood is burned incompletely and is an indication of improper use, damp wood, poor installation, or a poor wood stove design.

If you find a build-up of creosote in your stovepipe or chimney, have the chimney swept straight away by a qualified and competent chimney sweep.

Burning wood, like any other combustible material releases pollutants, mainly in the form of particulates and gases. The degree of pollutants is related to how efficiently (or inefficiently) the stove is operated. The main issue with wood burning stoves is the formation of creosote.

If smoke is cooled below 121 degrees C, the gases in the smoke liquefy, combine, and solidify, forming creosote. As a liquid, creosote can run down the insides of pipes and chimneys. It can also form a hard layer, by coating the insides of pipes and chimney liners. It is the cause of most chimney fires and the main reason chimneys and pipes have to be cleaned and inspected 2 – 3 times per year by a suitably qualified person.

You can minimise creosote buildup by following the tips above, you can also purchase “Flue & Chimney Cleaner” (Stovax are the brand we use). It helps limit the build-up of Tar, Creosote, and Soot in the Chimney and dries out the wet and sticky tar so that it will then loosen and fall down to the bottom of the firebox which can then be easily cleaned out.

Creosote Build Up Causes
  • Operating the stove at a too-low burn rate. Especially in air-tight stoves, if you damper the stove down, for a long, low burn, you will create a fire that emits unburned tar vapours into the venting system. The temperature of the flue gases will be relatively low and vapours will likely condense inside the pipe or chimney flue.
  • Using the wrong type of fuel. Burning green, wet, or excessively dry wood can cause creosote build-up. See our log guide here.
  • Oversized flue or improper connection. If the chimney isn’t quickly drawing the combustion products to the outdoors, due to an oversized flue, an excessively long stovepipe, or too many elbows in the stovepipe – all of which tend to increase the amount of time the smoke stays in the venting system – then the smoke will tend to condense in the flue, forming creosote.
  • Poor stove design. Airflow into an air-tight stove can be closely controlled, in some cases to the point that the user can extinguish the fire by closing the air controls! This type of stove doesn’t burn fuel efficiently, lots of fuel is wasted in the form of smoke, which condenses in the stovepipe and chimney as creosote.
  • Too big a stove for your needs. If the kW output of your stove is significantly higher than is required for the room, it is likely that you’ll burn the stove low to ensure the room doesn’t become uncomfortably warm (see point 1 above).