Thursday, March 24, 2016

Fact Checking Your Brick Oven

What are the real stats on your brick oven?

  Excluding appearance, which can range from industrial through space age, there are five stats to pay attention to when comparing brick ovens.

#1 Shape.  The shape and proportions of a brick oven effect function.  Dome height can vary from Napolitano 'low vault' domes
to classic 'Pompeii' shapes.  Low vault domes are
best for broil situations and are suited to pizza.  Pompeii or higher domes are more versatile, encompassing pizza as well as all other baked, roasted, slow-cooked, and smoked foods.

#2 Mass.  The thickness of the dome is where the heat of the fire is stored and released.  Cast refractory domes that come in kits tend to have thinner shells thus less mass.  This will work if you want quick high temperature.
Fire brick domes, such as the ones I build, are 4.5" thick and store a great deal of BTU's.  For restaurant and bakery ovens I double that thickness (9") creating an oven that will stay very hot, loosing only 100 degrees in 24 hours.

#3 Insulation.  The BTU's (heat) that the wood fire puts into the mass of the oven will be lost to the atmosphere.  Slowing the loss down requires more insulation.  The floor of the oven MUST be isolated from the heat-sucking masonry it sits on.  I use 4" of Foamglas, a porous high temp block.  One inch ceramic board insulation turns to mush when wet.  A less expensive below-floor insulation can be cast using vermiculite and Portland cement.  Most commercial oven shells come with 2" of blanket insulation.  I recommend 4-6".  The extra expense is repaid in efficiency.  This is true for your home but that's another big topic.

#4 Draft.  Ovens that have flues need a chimney that will draw the smoke up and away from the user.
The height and diameter of the chimney determine the draft.  For interior installations, I build make-up air channels so that the combustion air is coming from outside the house.  Without these, other devices in the house may suck air down the oven flue causing smoking.

#5 Fire.  Dry hardwood is a must.  Wet wood is inefficient.  Softwoods, such as pine, spruce, fir, hemlock, and cedar have very light ash and short-lived embers.
Since you want the fire in your oven, rather than consuming your house or yard, conforming to code standards regarding distance to combustibles is essential.

Whatever oven you end up with should have the best aspects of the above factors.