Now that is an interesting and very difficult question to answer.

No two ovens are the same.  An updraught oven is less efficient and will consume more fuel than a downdraught oven of the same size and 'oven fill'.  Large ovens will consume more coal than small ovens.

So it is very difficult to give one simple answer but as a rule of thumb and using loads of averaging to show how inefficient the bottle oven really was, lets say that 10 tons of coal is required to fire 1 ton of clay ware. 10 to 1. That's why clay, the basic raw material, was brought from Cornwall to The Potteries. Not the other way around.

In 1941, The British Pottery Research Association published a technical paper by R.J. Waller about 'The Firing and Performance of an Updraught Oven for Glost Earthenware.' This paper was based on technical research and showed exactly how much

In it they observed the firing of a 17ft 5" diameter oven, 60 feet to the top of the 'cone', set with 1200 dozen pieces (almost 5 tons) of earthenware product in a total weight of setting (including saggars) of almost 30 tons.

The oven took 28.5 hours to fire to 1060ÂșC.  The oven consumed 10 tons and 17 cwt of  coal - 'washed bituminous beans.'

Preparing coal for 'kindling' 1890s  Spode factory, Stoke?
Photos: Source unknown

The total cost of the coal to fire the oven in 1941 was 23 shillings - which is now £1.15 in decimal currency.

The efficiency of the oven, calculated from the data summarised in the heat balance, showed that less than 1% of the heat input was employed usefully in heating the ware and only 5% was used in the whole setting (including the saggars.)

Bigger ovens with more product would consume more coal whereas a small enamel muffle kiln would consume much less.

Hanley Deep Colliery, Hanley
Source unknown

Hanley Deep Colliery
Owned by The Hanley Deep Colliery, Shelton Iron, Steel and Coal Company Ltd., in 1937
Source of coal for The Potteries. The 'TEN FOOT SEAM' was mined here but it was not of outstanding quality
Photo: Terry Woolliscroft   Date: July 1975

Hanley Deep Colliery
Photo: Source unknown  Date: Late 1970s

The Coalfields of North Staffordshire

The North Staffordshire Coalfield

For definitions of unusual Potteries words go to The Potbank Dictionary here>