Eli5 How do gas ventless fireplaces work without electricity?


I have a propane powered vent free fireplace in my garage. It doesn’t get plugged in anywhere and it doesn’t take batteries. I get how the peizo works to start it but how the hell does it turn the gas valve on and off by itself? When I go from pilot light to on there is a delay to when you actually hear the gas start flowing. Then it will also click and just shut itself off sometimes.

In: 10

It’s hard to know without knowing the exact model, but it’s likely got a thermal switch.

You may be aware of a thermal couple, a type of temperature sensing equipment that creates a small voltage when it’s heated.

Thing is, if you pack enough thermal couples together into a bundle and serialise their output you can achieve a high enough voltage to do things like actuate a valve.

There’s probably an electric valve actuated by a thermal switch that’s heated by the pilot flame.

There is a device called a thermopile located next to the pilot.

When you light the pilot, turning the knob allows gas to flow, and the piezo spark ignites it.

The thermopile, which consists of a stack of dissimilar metal, generates a small voltage from the heat of the flame (this is the principle of the thermocouple). By stacking, the small voltages add together to produce enough power to activate the gas valve.

That’s why these are quite safe; if the pilot goes out, the thermopile cools off, and the gas valve closes due to no power.

The [Seebeck Effect]( https://en.m.wikipedia.org/wiki/Thermoelectric_effect) is how the power gets generated to operate the valve. The Voyager space probes used plutonium to generate heat to produce power via a Thermo Electric Generator TEG. This process also works in the reverse in a Peltier cooler. The little desktop refrigerators and many electronic devices use this to cool them.

actually a good question. this guy goes into some detail about it https://www.youtube.com/watch?v=xvFZjo5PgG0