Installation guide

Pompeii Oven Instructions
© Forno Bravo, LLC 2007. All Rights Served. Ver. 1.2 64
Appendix 4. Thermal Mass Primer
Overview
Thermal mass and insulation are the two primary
characteristics that describe an oven's ability to absorb
and hold heat, and make it useful for cooking. An oven's
thermal mass describes the part of the oven that is heated
and provides heat to the oven chamber, while insulation
describes the oven's ability to stop heat from escaping, or
leaking, out of the oven -- where it is lost.
Thermal Mass
The thermal mass of a wood-fired oven can vary widely,
from a simple 1 1/2" thick clay shell to a massive 12" thick
brick bread oven. The barrel vault oven described in books
and on the Internet has a 9” thick dome and hearth, which
is much too massive for backyard cooking or a commercial
pizzeria. When considering which oven is right for your
application -- whether it is in your home or in a restaurant,
you should take a number of factors into account.
Too much thermal mass is very bad. Heat, like most things
in nature, likes equilibrium. If one side of a thermal mass,
such as a block of concrete, is hot and the other is cool,
nature will try to balance that heat by moving it from the
hot spot to the cool spot -- eventually reaching equilibrium
where everything is just warm.
In a wood fired oven, this means that it is strongly
desirable for the thermal layers in an oven's dome and
cooking surface to be completely hot when it is time to
cook. If they are not, the heat in the oven will continue to
"wick" away from the oven chamber, in an attempt to
create equilibrium in the whole thermal mass.
For example, if it requires 6 hours to fully heat up an
oven's thermal mass, that oven will not cook well for the
entire six hours it is heating up. Even though you are
adding more and more fuel, the heat is moving away from
the oven chamber as fast as you can replenish it. With this
design it is virtually impossible to maintain the high heat
required for the perfect 3-minute pizza.
At the same time, too little thermal mass can also be
problematic. While an inexpensive clay oven shell might
heat up quickly, it does not posses the heat holding ability
to cook larger volumes of food, larger numbers of pizza, or
bread. A thinner oven will begin start giving up heat as
soon as the fire has stopped, creating a range of problems
for the chef. As a side note, the Forno Bravo ovens all
have enough thermal mass for typical home baking bread
or roasting a turkey.
The composition up of an oven's thermal material is
critical. Alumina and silica are two materials that have both
high heat conductivity and high heat holding capability. An
oven rich in these materials will heat up more quickly, and
hold heat longer, than an oven made from clay, brick, or
even standard firebricks.
By tailoring the thermal mass of the oven to the intended
us, either residential or commercial, bread or pizza, it is
possible to produce the optimal oven for a range of
applications.
An oven built using 2"-3” of engineered refractory is
perfect for a vast majority of home and garden
applications.
Insulation
While too much thermal mass is bad, there is no such
thing as too much insulation. Luckily, through modern
manufacturing advances it is possible to readily and cost-
effectively insulate a wood-fired oven. In fact, it is possible
to make insulation cost and space trade-offs for a
particular oven installation.
Which is a good thing. As the optimal oven design
demands a thermal layer that can be efficiently heated