Ideas for Controlling 7500W Heater

Hardware
1

Looking for some advice on how to integrate an electric heater into my setup for better control. The unit in question is a 240V single phase 7500W electric heater that I plan to occasionally use in my garage. It only has very basic controls, a switch to control to one of two heating levels, and a dial thermostat with no actual temperatures.

The thermostat is built into the unit, and I expect it to be of little use, being so close to the heat source. I have a temperature sensor on the other side of my garage that is integrated into my setup through MQTT already that I would prefer to use.

The main question is how to control the unit with a thermostat in Home Assistant. It is possible to hook up an external thermostat on this unit, but it is only compatible with a 240V line voltage double pole thermostat, which in my mind is not any different than just cycling power to the entire unit. Please correct me if this doesn’t sound right. Below is the wiring diagram for reference.

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My first thought was to use a smart line voltage thermostat, of which I found this one:

…but it only works up to 3600W, so that doesn’t seem like a viable option.

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My next thought was to use a heavy duty smart switch to simply cycle power to the whole unit, using my existing temperature sensor, and the Generic Thermostat integration:
https://www.amazon.com/120-277VAC-Electric-Compatible-Certified-14285/dp/B00YTCZZF0/
I don’t see any issue with this approach, other than it being a bit expensive. I think it should be possible to wire up this switch to the external thermostat connection as well, so long as I power the switch in parallel to the heater, but I don’t know if there would be any advantage to this approach vs just wiring the unit inline with the power going into the heater.

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Trying to think of other options, maybe something with ESPHome, like one of these:
https://www.amazon.com/dp/B085HP2GJX/
…which I think can be flashed with ESPHome, but that relay module is not rated for nearly enough power.

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I would prefer not to make modifications to the heater that would void its warranty (or potentially compromise safety), but am open to hearing any ideas. Thanks!

2

You don’t need to switch the full load since the unit has a contactor inside which will do this for you. You just need to put a smart relay in place / in parallel with the ‘selector switch’.

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Use a simple setup of an ESP controlling a relay which you put in as put my above comment.

Putting the relay in parallel with the selector switch should be of minimal modification / intrusion and this way the factory switch is still operable.

3

I like your line of thinking, but that selector switch is also passing the full current of the device, I believe. So putting another relay in parallel would require that relay to also be rated for the full current, would it not?

This is a physical switch on the rear of the device:
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Your comment did give me another idea just now, though. I hadn’t considered using this switch as a method of control for the device, but I could very easily do that with a SwitchBot.
I briefly considered using a SwitchBot on the main power button at the front, but decided against it since that button is right below the heater output, and would probably not be great for the battery in the device. Being located at the back near the air inlet should be much less of a concern.

4

No it isn’t. The item listed as ‘KM’ is a contactor which is switching the full load.

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5

I’m using the Enbrighten Z-Wave Plus 40-Amp Indoor/Outdoor Metal Box Smart Switch for my garage heater and it works great. The other benefit is that it reports energy usage to track how much that sucker is costing you every minute. :wink:

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All about contactors:

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Oh, right, that makes sense. I missed that on the diagram, thank you for explaining that.
So the thermostat, built-in or external (and selector switch) are only passing current to close the contactor and run the fan, which seems like it shouldn’t be much more than a couple hundred watts. In that case, there are a lot of options for control, and an ESP would be a simple and inexpensive solution.
Thanks for the help!

8

I am definitely interested in the power consumption, but I already have a couple smart meters installed for this, one in my main panel, one in the garage subpanel.

I highly recommend this if you are looking to monitor many circuits and get insights for your entire home.

…then again, maybe I don’t want to know how much I’m spending on this :face_with_peeking_eye:

1 Like
9

Ive recently swapped out a few line voltage thermostats to a 24 vac honeywells using this type (RIB) relay. You’d need a 24 vac power source, I use a simple plug in transformer or hard wired transformer for this.