How a stove works

Today, stoves are available in many different shapes, styles and sizes. Each will also have different features according to the manufacturer’s specification for a particular model or range so it’s important to find out how a stove works.

For example, this can vary from the quite basic with just primary air for combustion; to more advanced technologies incorporating an airwash system for the window and a ‘cleanburn system’ with secondary air introduced higher in the firebox. Certain stoves may include an ‘external air’ facility and others are fitted with integral boilers to provide domestic hot water and run radiators.

As each stove operates differently depending on the manufacturer’s design of the airflow, grate and control systems, the SIA strongly recommends you refer to the manufacturer’s instructions for specific details.

Accordingly, the following is an generic explanation of the features you may wish to consider when choosing the right stove for your home, and should be read in conjunction with the manufacturer’s specific operating instructions for the appliance you are using:

Primary Air

This is the air that is used for initial combustion of solid fuel and normally comes in low down in the firebox. Usually, there will be a control on the front of the stoves to adjust the amount of air entering the firebox and, thus, giving you the opportunity to regulate the intensity of the fire. This, in turn, will alter the heat output.

Primary air may be used to start a wood fire but is not normally recommended for use once the logs are burning.


Airwash is a design feature that uses a specially placed vent or vents to draw in cool air from the outside to ‘wash’ over the inside of the glass. This helps to keep the glass cleaner for longer, allowing you to enjoy the glow and flames to the full. It is also used as primary combustion air when burning wood.

Convection Air

Where stoves have a convection system, cool air from within the room is drawn into the convection chamber, the air is heated and rises and, within a few minutes, the hot air flows out into the room. The cooler air continues flowing in and is then heated, maintaining added heating efficiency.

Some models may also incorporate, or have the option of, an electrically-operated fan to boost the convection process and provide a quicker warm up time within your room.

Cleanburn combustion or Secondary Air/Tertiary Air

Introducing pre-heated, secondary/tertiary air into the firebox at a level above the fuelbed allows there to be combustion of unburnt hydrocarbons in the smoke. This ‘cleanburn’ process can improve the heating efficiency you obtain from your fuel and give you an improved flame visual. It also helps reduce the levels of emissions from the stove by burning off any excess hydrocarbons in the smoke before it vents into the chimney system.

External Air

All wood and multi-fuel stoves with a heat output above 5kW require the provision of additional air into the room for combustion. An External Air facility allows this air to come directly from outside your building rather than through a vent into the room, thus eliminating draughts and adding to the overall heating efficiency.

Boiler stoves

Stoves with a built-in boiler are designed to provide domestic hot water and/or run radiators as part of a stand-alone system. The number and size of radiators you can operate will depend on the ‘heat output to water’ of the particular model.

Alternatively, you can ‘link up’ some boiler stoves with your existing heating system. The ‘link up’ system may depending on the model be able to connect with gas or oil sealed heating systems, combi’s, underfloor heating, and solar panels by using advanced electronic controls. This will help you to save money on fossil fuels and reduce your reliance on single source heating.

In both cases, it is strongly recommended that your requirements are discussed with an experienced and appropriately qualified stove retailer and/or heating engineer.

Smoke Control Areas

Most town and city homes are located in Smoke Control Areas as designated by the Clean Air Act 1993. Within these areas:

  • there’s a limit on how much smoke you can release from a chimney
  • you can only burn authorised fuel, unless you use an ‘exempt appliance’

To burn wood logs on a stove at an address within a Smoke Control Area, the model installed must have been granted Defra exemption. This exemption is given only to appliances which have been independently tested to meet Defra’s low emission requirements. If you don’t have a Defra exempt stove you may only burn smokeless fuels on a multi-fuel stove within a Smoke Control Area.

There are penalties for breaking the rules. You can be fined up to £1,000 for burning unauthorised fuel without an exempt appliance.

You can check if your stove model is Defra exempt by checking on the Defra product listing here. Alternatively, if you are thinking of buying your first stove or replacing an existing model, take a look at the clearSkies product listing – all appliances on this list with a clearSkies Level 3 or above have been independently verified as meeting Ecodesign AND having Defra exemption.

Wood burns best on a bed of ash with primary air so woodburning only versions of stoves may have no grate and no ashpan. Other wood burning only versions may have a grate for easy ash removal, but this would normally be set to a flat position to allow ash build up when burning.

All multi-fuel stoves can burn wood; however multi-fuel stoves have a raised grate. This allows the ash and cinders from smokeless fuels to be riddled into an ashpan below, maintaining the airflow through the fuel bed and, hence, creating the optimum conditions for efficient combustion of those particular fuels. Multi-fuel stoves may have either an internal or external control system for riddling the grate.

How to choose the right stove for you

We would always recommend taking the advice of an appropriately qualified independent retailer, manufacturer or an appropriately qualified installation engineer before selecting your stove. The key factors to take into consideration, many of which are explained above, are:


  • The style/aesthetics you desire
  • Heat output appropriate for the room/space you wish to heat
  • Fuel type – woodburning only or multi-fuel?
  • Do you wish the stove to heat water as well as the room?
  • Are cleanburn, airwash and efficiency important to you?
  • Do you wish to burn wood in a smoke control area?
  • The answers to these questions will narrow your selection down and help guide you to the ideal stove for you.

Consumer Information

The SIA is here to help consumers with all things wood-burning stoves and biomass appliance related. From understanding the benefits of Ecodesign stoves, to the importance of using dry wood and a guide on how best to light the stove.