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During the extreme cold we are experiencing throughout much of the
United States this winter many people attempt to use their fireplace as a
source for supplemental heat. But what most homeowners are unaware of
is that fireplaces are designed for ambient fires only, and are not
meant to be used for heating purposes.
Open fireplaces are inefficiently designed so that most of the heat escapes into the flue, rather than the home. In fact, open fireplaces use heated room air for combustion, thereby lowering the temperature inside the house.
Exception: Rumford style fireplaces.
According to the Midwest
Chimney Safety Council, chimney sweeps are reporting record calls for
chimney service, no doubt due to the unusually long and bitterly cold
winter. What the chimney sweeps are finding out is that their customers
have been using their fireplaces as a heating source, rather than for
just the occasional friendly fire. That is when trouble can happen.
Open
wood-or gas burning fireplaces are designed with clearances to
combustibles set at certain distances with the idea that people will use
their appliance for short periods of time – up to four hours in
duration. Once that time has been exceeded, or before if improperly
installed, the nearby combustible materials may overheat and ignite.
Combustible headers and studs, which are hidden from view by finishing
materials may not be properly installed with proper clearance, which
makes matters even worse. Unfortunately, improper construction around
fireplaces is a common issue and many house fires have been the result.
Nearby
combustible wood may pryolizes over time due to exposure to heat
through the masonry or metal fireplace. Pyrolization is the chemical
alteration of wood, which lowers the ignition temperature significantly.
Wood normally ignites at 500 degrees, but pyrolized wood can ignite at
180 degrees or lower.
After a Raytown, Missouri house fire in
2009 Fire Investigator Gene Padgitt was requested to find the cause and
origin of the fire. The customer had used their masonry fireplace as the
sole source of heat for three days while they had no gas after moving
in their new home on a Friday. Combustible wood framing, which was
improperly installed above the fireplace without proper clearances,
ignited due to exposure to heat for the prolonged period. Padgitt said
that this scenario is all too common and that unfortunately, he sees it
often.
In yet another fire investigation in Topeka, Kansas in 2012
Gene found that the homeowner used a manufactured gas fireplace for
seven days straight when wood framing, which was properly installed,
ignited. The fire caused a total loss. The homeowner thought that he
could heat his house with the fireplace.
This type of burning is
called "Over-firing" in the chimney and hearth industry. The fact is
that masonry fireplaces do not come with a homeowner's manual, and
rarely do new home buyers find a manual for their manufactured
fireplace. So it is up to the homeowner to get operation information
from his chimney sweep or from websites.
Certain wood and gas
appliances are designed for heating, while others are designed for
ambient fires. Since there are no standards in the industry that have
been adopted for masonry fireplaces, Padgitt suggests that homeowners
use common sense when operating a fireplace or stove. He suggests the
following:
Appliances designed for ambient fires:
- Wood-burning manufactured fireplaces (read the manufacturer instructions)
- Wood-burning masonry fireplaces
- Gas-burning manufactured fireplaces (read the manufacturer instructions)
- Gas-burning masonry fireplaces
Appliances designed for heating:
- Wood-burning freestanding stoves with proper clearances
- Wood-burning fireplace inserts in masonry fireplaces
- Wood-burning masonry heaters
- Direct-Vent Gas fireplaces (per manufacturer instructions)
- Non-Venting
gas logs in masonry fireplaces (read the manufacturer instructions
which likely state that they are not to be used for longer than four
hours at a time)
All gas and wood burning appliances should
be installed by a professional technician, and inspected annually and
swept or serviced as necessary by a professional chimney sweep or
certified technician. Wood-burning stoves and inserts should be swept at
least twice per season if used for primary heating purposes, or used on
a regular basis in order to remove flammable creosote.
Note:
Non-Venting gas logs and wood-burning fireplace inserts should never be
installed in manufactured fireplaces. To do so voids the warranty on the
fireplace, and alters the fireplace which is a code violation. Any
alteration can be a fire hazard.
Resources:
Masonry Heater Association of North America
Chimney Safety Institute of America
Midwest Chimney Safety Council
National Fire Protection Association
Masonry heaters are
site-built wood-burning appliances that radiantly heat a home with wood. They are very efficient and use relatively small
amounts of wood heat without the use of electricity, gas, fans, or ducts. Wood
is burned in a firebox, which connects to channels inside a large thermal mass. After the fire is out the appliance gradually
radiate heat to the living space for many hours without causing large
temperature fluctuations or drafts. 