Direct-vent gas fireplaces are made in many different designs.
Standard one-sided models are the norm, but you’ll also find two-sided, three-sided (peninsula), and four-sided (island) styles, as well as bay-window shapes and corner units. Heat-N-Glo even makes a three-sided Pier Bar unit that can go at the end of a bar.
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.
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 one 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 the output rate by the 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 percent efficiency.
Controls and options for direct-vent fireplaces 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.
But if the pilot isn’t lit, the main gas valve won’t open. In fact, Blaze King’s Split Second(tm) Safety System shuts off the gas within one second if the pilot light goes out.
You can use a wall switch, a thermostat, or a remote control to operate many types of direct-vent systems. Some remote controls have adjustable thermostats, blower-speed controls, and flame-height adjustments.
Other options for direct-vent fireplaces include variable-speed fans to boost circulation, special trim kits, propane gas conversion kits, decorative screens, firebrick-style fireboxes, and more.
In some parts of the country, codes allow the use of vent-free fireplaces. Vent-free or “no-vent” fireplaces, made by several manufacturers, have an oxygen-depletion sensor to shut off the gas if the oxygen level ever drops below a preset level. In addition, their burners produce only very low levels of carbon monoxide.
Because all their heat is recirculated into the room, these have very high efficiency ratings. On the downside, they have a much smaller and less realistic fire than other fireplaces. Also, product directions usually require you to leave a window slightly open during use.