Any central heating appliance that
burns fuel requires air. Builders installing
furnaces, boilers, or direct-fired water
heaters must provide a source of air adequate
for three purposes:
• to provide oxygen for combustion of
the fuel
• to ventilate the space around the
appliance, preventing it from overheating
• to dilute flue gases and ensure their
safe passage up the chimney
Depriving an appliance of the air it
needs can cause serious problems. A
lack of sufficient combustion air can
cause incomplete combustion, which in
turn increases the production of poisonous
carbon monoxide and other dangerous
gases. Inadequate combustion air
also causes excessive soot formation in
oil-fired appliances, which significantly
reduces efficiency.
A lack of ventilation air, on the other
hand, can