Gas fireplaces generally do not require electricity and many have no fans. Exhaust is passive, and thermostats use a thermopile that generates a small current f

Gas fireplaces generally do not require electricity and many have no fans. Exhaust is passive, and thermostats use a thermopile that generates a small current from the heat of the pilot light. The pilot light is started manually with a piezoelectric starter, or a lighter. Gas fireplaces are slightly less efficient than high-efficiency furnaces because some heat goes out the exhaust.