What Is Direct Vent?

On a cold day, a fire is the perfect focal point for quiet conversation, reading a good book or a little romance. In fact, when it comes right down to it, nothing quite matches the warmth and ambiance of flickering flames in a fireplace. But what if your home doesn't have one? Take hearth! New direct-vent fireplaces may be your answer.

Although they look very much like traditional fireplaces, direct-vent units are, in many ways, the fireplaces of the future. Through technology, they have solved many of the problems associated with their wood-burning forebears.

Unlike traditional mortar-and-brick masonry fireplaces with foundations and chimneys, direct-vent units take advantage of zero-clearance technology. They are prefabricated from metal and designed to be installed in wood-frame construction without a foundation or-*put something here*nd this is the big difference between these and any other fireplace--a chimney. They burn so efficiently, they can be vented directly out a wall. This means they're much easier and less expensive to install than masonry units and you have much greater flexibility in their placement.

Direct-vent fireplaces burn natural gas or propane, not wood. But direct-vent models are different from conventional gas-fired fireplaces that require a through-the-roof, Class B flue to carry away hot, combustion gases. They burn efficiently, extracting most of the heat from the combustion gases and sealing the combustion off from interior rooms. A direct-vent model has a glass door that is securely sealed to prevent leaks of combustion products into the room. Air to feed the flame enters from outside and the relatively cool combustion gases are exhausted through the wall-mounted vent (if you prefer, you can also vent it through a roof).

Because they are gas-fired, these units address the serious problem of wood-smoke pollution that grew to crisis proportions in some regions about a decade ago. Unlike wood-burners, these gas fireplaces give off virtually no particulates.

Like all gas-burning fireplaces, they're much easier to use than wood-burning units because you don't have to buy, haul, chop, start and continually feed wood to the fire. And you don't have to scoop out the ashes or sweep the chimney. With gas, you just turn on the fire with a knob, a switch or even a remote control. Or you can let a thermostat do the job. When in use, they only cost pennies per hour to operate.

Heating Up

Most of these units have passageways that direct room air around the firebox /heat exchanger, then return it to the room. Some come with fans to boost this circulation; with others, fans are an option. These fireplaces garner efficiency ratings that approach those of gas-fired furnaces --in the 78 percent range. (This means they convert 78 percent of the fuel's potential heat to usable heat.)

Gas-fired fireplaces, like other gas appliances, are measured by their "Btu" per hour input or output capacity, depending upon the manufacturer. A Btu (British thermal unit) is equal to the amount of heat required to raise 1 pound of water 1 degree Fahrenheit.

Input capacity refers to the amount of gas burned without taking into consideration the percentage of heat lost through the flue. Output capacity refers to the total usable heat generated. Most manufacturers use the input capacity figure because it's always larger than the output. If you're concerned about how much heat a fireplace will generate, the output figure is the one that's important. If you want to know how efficiently it will use its fuel, figure the Steady State Efficiency rating by dividing its output rate by its input rate.

Input ratings vary, and some units have a range, depending upon the flame's setting. If supplemental heat is important, choose a model with plenty of output. The Mendota DXV fireplace, for example, has a thermostatically-controlled, variable two-level burner that can deliver from 25,000 to 40,000 Btus per hour with 75% efficiency.

Sizes vary. You'll find units from about 30 to 48 inches wide and about 24 to 30 inches high. They are typically quite shallow --from 13 to 18 inches deep.

Nearly all manufacturers make both top- and rear-venting models. Where you need to vent a unit upward because there isn't a straight shot out a wall, top-venting types work well. Depending upon the model, vents may run vertically or horizontally for quite a distance --up to 25 feet or more.

Controls and options

Controls and options vary from one manufacturer to the next. Some models have a standing safety pilot light that burns continuously to light the main burner whenever the gas is turned on. Others have electric spark ignition, to save energy, or a piezoelectric ignition, often chosen when there isn't an electrical hookup at the fireplace. Some of these types use a millivolt generator so the fireplace can operate even if the power goes out.

As mentioned above, you can use a wall switch, a thermostator a remote control to operate many types. Some remote controls have adjustable thermostats, blower speed controls and flame-height adjustments.

Because installation is relatively easy, it usually costs about $350. Prices for the fireplaces, of course, vary widely, depending upon size, style, finish and various options. You'll find they start at about $750 --a small price to pay for the value, comfort and enjoyment a new fireplace will bring your family.