Legislation and bodies such as HETAS regulate and recommend minimum efficiencies for solid fuel appliances in the UK and across the Europe's single market.

The 'CE' legislation requires all stoves sold in the European Union to declare their tested efficiencies and prohibit the sale of stoves that fall below these minimums. UK manufacturers have had a exemption that ends mid 2013.

Net and gross efficiencies

All figures quoted by modern manufacturers are net figures. These come in higher than gross figures, an approximate gross figure can be obtained by dividing the NET % by 0.9. The difference between net and gross figures is that net does not not account for the heat wasted in boiling off the water present in the fuel.

It has often been said that efficiency figures are more a test of the assessors ingenuity than of the appliance. To be born in mind that how the fuel is arranged in the firebox can vary the test results but anything up to 10 per cent. Also the figures ignore heat gained or lost outside of the appliance, this is especially significant with inset or wetback stoves.

Comparisons to in other areas

Despite all the above criticism of the test figures wood stoves do compare very favourably with almost all energy intense human activities.

Comparisons of popular stoves

I term appliances with efficiencies over 80% 'high efficiency' although other retailers will differ. Clearview were recently defended their position against an advertising standards complaint that their stoves reach the "highest environmental standards", by arguing efficiency is only one, amongst many measures, of the a stoves environmental credentials.

Few appliances come in below 70% these days, although there are often other advantages to 'low efficiency' stoves such as longevity, ease of lighting and purchase price.

Many modern stoves achieve their high efficiencies with the use of firebricks to line the firebox, these bricks have a finite life and will probably require replacing every few years.