Hardware recommendations for 3-button fireplace switch

Hardware
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I have a gas fireplace with millivolt control via a dumb wall switch. I want to convert it to smart control with a dry contact relay. Looking for hardware recommendations. I already have a spare Shelly 1 that is a good candidate for the relay, but I’m very unsure of the switch.

I want a wall switch that goes in the place of the existing dumb switch. It needs to be the size of the conventional single gang wall switch that it’s replacing for WAF. I want it to have 3 buttons - one each for “off”, “auto”, and “on”. Off & on would force the fireplace to that state, whereas auto would let it be managed by HA according to programmed time and temperature setpoints. The currently selected option needs to be visually indicated (I’m assuming I can turn off the previously selected switch when a new one is activated). I do not want extra buttons that are confusing (again for WAF), it needs to be a simple 3.

I have Z-wave and Zigbee already (using z2mqtt), so these are options. Theoretically, a scene switch should work since the relay will be doing the actual switching, but I’m only finding smart load switches that meet my criteria. In theory this is totally possible but wanted to check here in case people have any bright ideas or good advice.

And yes, I will also be wiring in hidden dumb switches on the millivolt system to force “off” and “on” states that bypass the relay. This will ensure that a safe “off” state can be manually enforced, and that the fireplace can still be turned on during a power outage that takes out HA and the relay (our primary heat is electric so this is a critical backup).

So, any hardware recommendations for a 3-button switch that fits a single-gang junction box, with indication of which switch(es) are “on”? I am willing to use a different relay or an integrated system if there is a good option I’m not aware of.

Thanks in advance!

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What is “millivolt system” to start with?

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A millivolt system is the common control approach for gas fireplaces. Basically a pilot light is always on, and heats a thermopile that generates a tiny voltage (millivolts). The main gas valve is operated by this voltage, not mains power. This ensures that (1) the gas valve cannot be opened if the pilot light is not lit, and (2) the gas fire place can still be operated even during a power outage.

If your gas fireplace is like the 99% of fireplaces (in N. America at least) then you want to keep mains voltage well away from the wiring. The wiring is tiny and not rated for any real amperage, and you could fry components with 120V. So it’s neccesary to use a dry contact relay to do any smart switching on the millivolt wiring.

It’s described well in more detail here if you’re interested in reading more.

4

Thank’s for that, didn’t even know about that kind of approach.
Anyway, if you want to use a relay to switch few mA at few mV, you shouldn’t use normal power relays, they are not designed for that. Use signal relay instead.
Typical power relay contacts are rated for min 100mA/5V for reliable long term switching. They need certain wetting current to “clean” the oxidation layer on contact surfaces.

1 Like
5

Ah interesting, thank you!