“All right, but apart from the sanitation, medicine, education, wine, public order, irrigation, roads, the fresh water system and public health, what have the Romans ever done for us?“. So the quote goes from Monty Python’s Life Of Brian. To that list you can also add Clay Ovens. No, honestly! The Roman’s built and cooked in clay ovens and, in common with most of their innovations, they conducted experiments in order to perfect the process of construction. Luckily for us, they also wrote it down!
Sometime between 70 and 15 BC, Roman architect Vitruvius, recorded the shape and proportions of the ovens in use during the 1st century BC. The most important measurement he recoded was that of the height and width of the oven entrance. This happens to be one of the questions I get asked most on this blog so I thought it was time to pass on Vitruvius’s wisdom to you all. I’m happy to say that it is very straightforward, here it is:
The height of a wood-fired oven entrance should be 63 percent of the height of the inside dome. The width of the door should be half that of the oven diameter.
Got it? So, all you need to do is make a note of the height of your sand former during construction and multiply that measurement by 0.63, for the entrance height, and obviously just divide it by 2 for the entrance width. Simple!
But why is this proportion so important? What does fire need in order to burn? A fuel source and oxygen, right? (Yes Simon we knew that. We are not idiots you know!). OK OK! So, When the oven entrance is just the right size it is able to draw in oxygen from the entrance where it combusts, flows around the curved roof of the oven, after which the exhaust gases flow out of the top of the entrance. If the entrance is too small, exhaust gases are prevented from escaping (they mix turbulently with incoming oxygen), they pool in the oven roof and will eventually extinguish the fire. Too large and the oven will be inefficient, losing lots of valuable heat through the gaping entrance.
A 1684 depiction of Vitruvius (right) presenting De Architectura to Augustus (from Wikipedia)
The design I propose on this blog, with a chimney at the front of the oven, just behind the entrance, will help to alleviate many of the problems described above. However, it is still crucial that the entrance is the correct size in order that the oven burns as efficiently as possible.
There you have it! Next time you are firing your oven, think about good old Vitruvius scribing these instructions for future generations to use. I reckon he deserves a toast, don’t you? Cheers!