Fireplace Terms

Input Rate:

The rate at which gas is supplied to an appliance.  This is usually mentioned in BTU per hour.

Vent, Flue:

A passageway for transporting gases to the outside air.

Oxygen Depletion Sensor (ODS):

This is a device used in ventless products that shuts off the flow of gas if the oxygen level in the room falls to 18%.

Millivolt:  1mv is 1/1000 of a volt.

Millivolt’s are generated by heat from the pilot burner flame. Thus no electricity is needed to power a millivolt valve system (a millivolt valve system will operate during power failures).


Heat from the pilot will generate 24mv to 30mv. This in turn holds the electromagnetic coil open, allowing gas to enter the valve body and hold a pilot flame. It also acts as a safety device that will shut off the gas supply to the main burner and pilot when no flame (heat) is sensed.


When heat is applied to the thermopile, an electric current is generated in the range of 450mv to 750mv. When the valve coil reaches the minimum required millivolts, the valve will open and gas will flow to the main burner and ignite.


A thermodisk is a temperature sensing device. When heat is applied to the disk, a bi-metal plate will bend. This allows the electric current to activate the blower motor and ensures continuity.

Spill Switch/Safety Shut Off Device:

A temperature sensing device used on most vented appliances that will shut down the main burner and pilot if the unit has a blocked flue or if in a downdraft situation.

Cast Logs:

Concrete based material. Glow is very minimal on logs. Dense material, holds heat in longer, and is less costly than fibre logs.

Fibre Logs:

Ceramic fibre compound. When flame impinges on the logs, it produces a red glow on the logs. Very lightweight and fragile material.