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I plan on installing an outdoor heater that takes a 220 V power supply. Each side of the 220 V circuit powers one element in the heater, for a total of two elements. Can I put a smart switch on each hot feed in the 220 circuit, use the common neutral wire on both smart switches, and end up with separately controllable heating elements via the smart switch?

Transistor
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BobbyS
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    On the face of it, I see no glaring problems with this setup, but without knowing whether the heater is designed to safely operate with only one phase connected, it's difficult to give a definitive answer. Additionally, there may be code requirements that the folks over at DIY would know about. – vir Nov 04 '22 at 21:30
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    I think you're making an assumption there that it is dual 120V elements. That makes no sense from a design perspective, and would not be done because it would put the heater at a competitive disadvantage. (however there are cheap Chinese goods where the makers don't understand the US market and make things like this 120V, but those are unsafe and illegal to install (NEC 110.2). You need to revisit your facts. – Harper - Reinstate Monica Nov 04 '22 at 21:36
  • Hi all, thanks for the comments. the heater is designed to run one or both elements depending on a Single Duplex Switch Wall Plate and Gang Box 20 Amp Per Pole, sold by the heater vendor. It has one manual switch per element. I was wondering if i could safely put smart switches in - and if so what kind would be a good choice? – BobbyS Nov 06 '22 at 19:28

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Not likely. Outdoor heaters in the North American market that take 240V supplies (it's 240V actually, 220V is just slang) are not wired like that for good reasons. Mind you, there are cheap units on Alibaba where the manufacturer does not understand the North American market; however these are cheaply built, unsafe, and illegal (NEC 110.2) because they lack the safety certification that is required to sell or use in the US. (notice how everything in reputable bricks-n-mortar stores is UL Listed). If you're buying cheap garbage from overseas specifically to get dual 120V channels to control this way, don't.

Why no 120V? First, using 120V requires the added expense of running a neutral wire, which heaters do not need normally. That's a competitive disadvantage especially for replacing a competitor heater (now the buyer must re-run power cables!) Second, "only one element running" creates a significant imbalance load, which makes provisioning harder, especially if power-limited supply is involved (local transformer, generator etc.) It also makes voltage drop 4 times worse for no useful reason. Bad design.

So you will have a 240V-only heater with 2 elements.

But let's get back to your Y problem: How do you control that? (and how do you make this on-topic for the Electronics stack)? By hacking the heater, of course!

You can get UR-Recognized specific purpose contactors designed for the control of heating loads, and those can be used inside the heater. The coil on the contactor can be your choice of 24 volts, 120V or 240V depending on which is easiest for you to control. 24V plays well with Nest style thermostats, it's also very easy for Arduinos and Raspberry Pi's to switch with electronic-grade $2 relays. Being low-voltage, it can be wired with common #18 thermostat wire. UL-Listed 24-volt transformers designed to mount on standard electrical boxes are readily available in the $15 range.

Or you can get plug-in 24V transformers you plug into a smart socket LOL.

120V requires wiring using approved AC power wiring methods such as UF-B cable or THWN wires in conduit, however you can directly control it from the smart switches you mentioned earlier.

Harper - Reinstate Monica
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