Heat (and money) go up the chimney. Despite its undeniable aesthetic
appeal and that toasty feeling on your face, a crackling wood
fire in a traditional fireplace isn't your friend. It’s sending
most of its heat straight up the chimney, and its appetite for
oxygen can actually displace the warm air in your home with cold,
resulting in a net energy loss.
To keep smoke from back-drafting into the house, a fireplace
has to draw air from the outside. In most homes, this means cold
air will enter through leaky windows and other openings, forcing
warm air up the chimney. In a weather-tight home, a window will
have to be opened to provide air for combustion.
Add glass door and air-intake vent. If your fireplace sits above
grade in an exterior wall, and if local codes allow it, install
a box vent, lined with fireproof material, to provide combustion
air directly to the fire. This helps prevent warm inside air
from being lost up the chimney. Glass fireplace doors radiate
the fire’s heat but block the loss of interior air.
Two modifications can interrupt a fireplaces cycle of inefficiency
by stopping the loss of warm inside air. The first step is to provide
an alternate source of combustion air by adding a vent that opens
directly into, or in front of, the firebox. Second, a set of glass
fireplace doors prevents interior air from entering the chimney.
Wood-burning insert. Similar in function to a freestanding wood
stove but nested inside the fireplace opening, a wood-burning
insert offers much greater efficiency than an open fireplace.
The key is a heat-exchange chamber that surrounds the firebox;
room air, helped by an electric blower, enters this chamber for
heating and recirculation.
Adjustable vents in the insert doors provide combustion air for
the firebox, but air that enters the heat-exchange chamber is heated and returned to the room. The smoke stream exits through a metal
flue insert so no cross- contamination occurs with the air circulating
through the heat-exchange chamber.
Gas-fired insert. Although it relies on a heat-exchange chamber
much the way a wood-burning insert does, a gas-fired fireplace
insert has a sealed combustion chamber, so no interior air is
used for combustion. Instead, two metal flue inserts are used:
one for combustion air intake and one for an exhaust vent. It’s
convenient and efficient.
With no wood to haul in and no ashes
to clean out, a gas-burning fireplace insert offers convenient
use of a converted fireplace. The combustion chamber is sealed
off from the home’s interior; its heat is captured by air in
the surrounding exchange chamber and circulated by an electric