The trend towards outdoor fireplaces has really been exploding in recent years. An outdoor fireplace enhances the appearance and ambiance of any backyard. Obviously it's impossible to heat the entire outdoors, so you'll want an outdoor fireplace mainly for the look and feel it provides. Most people think of wood-burning fireplaces as the primary option. We chose a gas appliance for the backyard of our Project House, mainly for the safety and convenience it provides.
Wood creates the classic, traditional look and feel, but it's messier and harder to control, especially outside. Gas can closely mimic the look of burning wood, and it's much more controllable. Flame in a gas fireplace is steady, adjustable and even. If a firebox is designed to only burn gas, never wood, then it's considered a gas appliance.
Specifically, we chose a direct vent gas-burning firebox. These boxes utilize a sealed combustion chamber with a tempered glass front. The tempered glass is extremely hard to break. If it does break, it will not shatter, but it will crumple as a single piece, just like the glass in your car's windshield. That's a great safety benefit in case you have kids playing around the pool. You don't have to worry about broken glass outside.
All the air used for combustion enters the firebox through a double-walled chimney. The double-walled chimney exists solely to supply air to the sealed combustion chamber. The inner ring vents smoke and heat; the outer ring brings air in for combustion and cools the inner ring.
Backyard safety is a big issue at the Project House. We have a very tight backyard behind a zero-lot line house. The neighboring house is right on top of ours. We have to be extremely careful to avoid creating a fire hazard. Even the mildest breeze could blow embers or sparks into the pool, back towards our house or over to the neighboring rooftop. Soot or ash in the firebox could easily fall into the pool or onto the deck.
The Direct Vent System offers us a safety solution, because it basically creates a balanced flue. Fresh air enters the burn chamber at the same speed and in the same amount as exhausting air exits the burn chamber. This gives us a constantly burning flame outdoors that's controllable and clean burning. There's never a danger of sparks or embers drifting to the pool or the neighbor's roof. Heat radiates to some extent off the glass door, but not enough to heat a large area, especially with a breeze.
Double - WallChimneyThis same direct vent system offers great convenience for interior fireplaces as well. The direct vent fireboxes can be installed indoors or outside. They all utilize the same sealed combustion chamber with a sealed glass front as the one we have outside. All air for combustion comes from outside through a double-walled chimney. Outside air never flows into the room; it's used for (sealed) combustion only. Indoor air never reaches the combustion chamber to burn. The room heats up primarily because room air circulates around the firebox in a gap behind the burn area and reenters the room. So indoor air is heated because of the combustion of outdoor air, even though those two different streams of air never mix. Additional heat radiates into the room from the glass door.
Our direct vent outdoor gas fireplace gives us a flame that burns constantly and evenly, so there's no need for an outside fuel source to feed the fire. We have no need to maintain a constant supply of wood, and no need to keep a woodpile clean, dry and handy. You can put a box like this anywhere you can run a natural gas line - even on a rooftop or a deck, for instance. You can even control this fire with a remote control.
We don't mean to suggest that all outdoor residential wood-burning fireplaces are a danger. In the proper location (a bigger backyard than ours, for instance), there's nothing wrong with a wood-burning fireplace outdoors.
You've got to consider the elements and how they affect an outdoor fireplace. Rain causes metal to rust. Martin Fireplaces just introduced a firebox with a stainless steel face and interior. Once it slides into the chase, only stainless steel is exposed to the elements. Maintenance is easy in this firebox. You can clean it easily with a garden hose. The bottom of the box is built with a five-degree slant, so water will easily rinse away. It won't pool in the bottom of the firebox.
Wood BurningAn outdoor wood-burning fireplace requires some practical consideration. It's worth planning ahead to figure out the directions from which the winds blow most often, so you can build a fireplace that blocks the prevailing wind as much as possible. An outdoor fireplace doesn't need as tall a flue system as an indoor fireplace. The experts recommend about a twelve foot minimum, including the box. We want to give the soot, and all those rising embers and sparks, plenty of time to burn out. The flue on our outdoor fireplace is just about that height. Just make sure you have a termination cap at the top of the chimney to catch sparks. A termination cap works like a spark arrester on a motorcycle. It's a baffled vent designed to keep embers and sparks from escaping and creating a fire hazard.