STOVE MANUFACTURE

Cast Iron or Steel?

Originally, all stoves were manufactured in cast iron and this continues to be the preferred material for many quality stoves.

• Is excellent at radiating the heat from the fire to the room
• Has great strength and can be cast thick where required
• Allows attractive designs to be cast for the stove panels
• Is heavy and hard wearing

Modern manufacture has enabled the use of heavy gauge steel for the body of the stove. Usually complimented by cast iron doors and firebox components.

• Heats up and cools down quicker
• Allows modern designs
• Is lighter and cheaper than cast iron

Quality Control

Manufacturers will have a range of quality control measures and a number use ‘CE’ marking. This certifies that they have been independently tested to exacting European standards for both heating efficiency and emissions.

HOW STOVES WORK

Understanding the stove’s operational functions is essential to maximise efficiency and to care for it properly. Needless to say quality in design, material and workmanship are important.

Multi-fuel defines stoves that are capable of burning both wood and coal. There are also gas electric and oil stoves available, mainly in the Aga / Rayburn cooker style.

Wood and Coal have very different burning properties and for the reasons set out below should not be burnt together. Whilst an open fire can burn both it does so by letting over 75% of the heat produced go up the chimney.

Design

• Maximise the heat from the fuel used
• Give complete control of the rate the fuel burns
• Transfer as much of the produced heat as possible to the room

Operating - also see Air Controls & Air Inlet Channels

The stove must be operated differently when using either wood or coal to ensure that no combustible element of the fuel escapes un burnt. The right amount of air is important to the burning process otherwise soot, carbon monoxide and creosote can result. Too much air can cause similar problems by cooling the burning process and too little air can choke the fire.

It is important that the air controls are used correctly to maximise the efficiency and the size of the fire. Air controls need to be adjusted gradually and not abruptly.

The transfer of heat is achieved by passing the hot air of the fire over as much of the surface area of the stove as possible, this is helped by using internal baffles to increase the distance travelled by the hot air.

N.B. It is essential to buy the right size of stove to meet your needs.

The different burning properties of:

Coal:

• Is wood compressed over 1000’s of years
• Most of the original resins have gone
• Comprises a high proportion of carbon

Wood:

• Has a low proportion of carbon
• Has a high proportion of resins called, ‘volatiles’
• The carbon content is called charcoal and this is produced by burning off the ‘volatiles’ without air to prevent ignition

Manufacture

• Controllable and sealable air channels to let air enter underneath the grate for burning coal , (primary), in the middle and top for burning wood, (air wash and clean burn)
• Combustion chamber above the grate with access to the flue/chimney
• Door for the fuel to loaded
• Vision panel to watch the fire
• A grate for burning the fuel
• An ash pan to collect the fuel residue when burnt, which can be emptied
• Made of cast iron or steel that will both conduct and radiant heat in to the room

Burning coal

The air supply enters in the bottom of the stove through the grate which supports the fire bed. A ‘riddle’ will be required so that the airways can be kept clear.

Burning wood

The air supply enters in the top of the stove above the vision panel to ensure that all the ‘volatiles’ in the wood are burnt off before they enter the flue/chimney. Air coming into the stove this way keeps the vision panel clear of staining and is termed ‘air wash.’

Air can also be channelled into the middle of the stove to further improve the burning efficiency and this is termed ‘clean burn.’

Air controls

Opening all the air vents is only necessary when lighting the stove to generate the air flow required to light the fuel and draw the heat up the flue/chimney. The quicker the flue/chimney is heated the less condensation/creosote is generated.

Letting the stove draw too much air once the fire is established will reduce the heat output, allow unburned material to enter the flue/chimney, prevent control of the fire and reduce the life span of the stove.

Getting the most heat from:

Coal - achieved by ensuring that all the air entering the stove only does so from beneath the grate. The air passing through the grate to the coal keeps the grate temperature to safe limits and heats the air up as it passes through. The hot air will be attracted by any unburned coal so that hot combustion is assured with the heat being conducted into the room by the body of the stove.

Controlling the air reliably controls the rate of burning and maximises the efficiency of the stove.

N.B. Letting any other air enter the stove once the fire is established e.g. by fully opening the air wash or by having a faulty door seal, will mean that the stove may burn at a higher rate than it was designed to, i.e. it will over fire. Where this continues over a long period of time this may irreparably damage the stove.

Before adding new coal always riddle the grate to ensure an adequate air supply and never leave the door to the ash pan open.

Wood - ideally all the ‘volatiles’ need to be burnt before they enter the flue/chimney. This improves heat output prevents corrosive and potentially combustible tars coating the flue/chimney.

To ensure full combustion is achieved air is channelled to the top and middle of the stove to fully burn the wood and the ’volatiles’ it contains. Controlling the amount of air makes the system self regulating, but it is important that the air reaches all the ‘volatiles’ and is heated on entry so that it doesn’t cool the wood below ignition temperature. Good stove design achieves this with air wash and clean burn channels to keep the temperature as high as possible.

High burning efficiency is maintained by gradual and not dramatic changes in the air flow.

There is no need to supply air under the grate when burning wood for cooling purposes as there is insufficient heat in timber embers to cause any damage.

N.B. Allowing air to enter the stove through the grate would result in the carbon content of the wood burning first releasing large amounts of ‘volatile’ with insufficient air to burn it. This will reduce the efficiency of the stove and create the potential for over fire with extended flaming overheating the flue and damaging the stove. The fires search for air may also result in the flue catching fire.

AIR CONTROL & AIR INLET CHANNELS

Stoves are specifically designed to be airtight with controllable air inlets, apart from stoves designed to have there doors open when fired. It is the precise control of the air inlets that controls the rate of burn and the heat output.

Air wash and Clean burn

Fundamentally these are controllable air inlet channels built into the stove to help the efficient burning of the fuel, maximising the heat generated and minimising the emissions. How these air inlet channels are incorporated into the stove design that create the ‘air wash’ and ‘clean burn’ technologies:

The air controls and channels are termed, 'airwash', 'cleanburn' and 'primary'. This defines in which part of the burning chamber the air is drawn in by the fire and how it helps the stove to burn efficiently maximising the heat output:
• Air wash - this is the air inlet channel that draws air past the fire window to keep it clean and clear.
• Clean burn - this is the air inlet channel that draws air past the fire box into the upper middle chamber of the stove so that it is hot when it enters the fire chamber. This hot air is quickly heated to the burning temperature and efficiently burns any un burnt ‘volatiles’, ie particles that can be left after the burning process, giving cleaner emissions and increased heat output.
• Primary - this is the air inlet channel in the bottom of the grate essential for burning solid fuels and for starting the fire.

NB When burning wood, once the fire is established, the primary air channel must be closed so that the air wash and clean burn channels can be used.

When burning coal the air wash and clean burn channels are partially closed so that the primary channel can be used.

Proper use of the Air Inlet Channels

Burning Wood:

• Lighting the stove
  1. Open the fuel loading door
  2. Start the fire with kindling and paper
  3. Open the air wash inlet
  4. Open the primary inlet by 25%
• Fire establishes
  1. Add larger pieces of wood
  2. Close the fuel loading door
  3. Close the primary inlet
• Fire in flame
  1. Control with the air wash inlet
• Amount of logs
  1. Do not put logs above the clean burn inlet
• Heat output
  1. Burn at full heat for at least 30 mins per day to prevent build up of tars & creosote

Burning Solid Fuel:

• Lighting the stove
  1. Open the fuel loading door
  2. Start the fire with kindling and paper
  3. Open the primary inlet
  4. Open the air wash inlet by 50%
• Fire establishes
  1. Add more solid fuel
  2. Close the fuel loading door
  3. Close the air wash inlet to 25%
• Fire in flame
  1. Keep the primary inlet fully open until a glowing fuel bed is established
  2. Adjust the rate of burn / heat output with the primary inlet to suit
• Amount of solid fuel
  1. Do not fill above the clean burn inlets
• Heat output
  1. Burn at full heat for at least 30 mins per day to prevent build up of tars & creosote