Remotely controlling electric wall heaters

[mdesmarais]

Looks like there is an overheat failsafe- you need to make sure that stays in the circuit, no matter what.
There is also a fan delay- which implies that it does want to fan to run after the heater kicks off.

Again, what exactly are you trying to accomplish? That will influence what approach you take!

 

[BLH]

The maual shows the dial is a thermostat. That is switching the Line voltage On and Off to the heating elements.
4000 watts. That is about 16.5 amps current with a 240 volt AC Line Voltage.

 

[roussell]

Looking at the wiring diagram on page 3 and the replacement parts list - there is a fan delay so you don't want to just cut power to the heater as a whole. The fan looks to be powered independently of the thermostat and controlled by a separate thermostatic switch on or near the heating elements. Automating these while staying safe may get a little tricky (and a little more expensive).

If it were me I'd probably tie a double pole relay in just after the t'stat and reset switch. You'll need one rated for 240 volts and at least 20 amps resistive. I'd look for one with a coil voltage of 12-24 volts and then run low voltage wiring from each coil/relay/heater assembly to a central location where I'd switch them on/off with a smaller relay connected to a CAI board, weeder, Elk, or some other digital I/O board (search ebay for "ethernet relay" and you find lots of examples).

You could at this point - if you have a cool space in the heater, use a 120 volt coil relay instead and power it through a Insteon/UPB/Z-wave switch (I'd probably use an inline-linc Insteon, but others will work fine too)

Tying in the relay after the t'stat and reset switch keeps the safety features of the heater intact and stills allows for manual override and "max heat" setpoint adjustment at the heater. Using a low-voltage coil on the relay allows you to more easily run cable to your central control location.

I'll draw a diagram if the above is a little muddy.

Terry

 

[JeffCharger]

I did something similar for out propane fireplace at our cottage. I hooked up a second thermostat in parallel with the standard one. I then built some scripts to control it. I physically unplug the power to the second thermostat when not in use (summer).

I built in security so that to turn it on, you have to hit a special combination of buttons to actually turn it ON. The script detects if there's a ON command without the right combo of keys, and sends me an email to notify me. It hasn't failed in 3 years or so.

 

[tmbrown97]

What Roussell described is exactly what I was picturing. It's too bad there's so many of them - otherwise I'd do what Desert_AIP did in a heartbeat... but that would get expensive.

And I have to just say, I cringe at the thought of 40,000 watts of heating!! Then again, your electricity probably costs less than a quarter what mine does.

 

[LCARS]

What I'm most worried about is not having the heaters turned up high enough when I'm away and the temperature drops. I think it would be easy for me to get the house nice and toasty with the wood stove, dial down the heaters accordingly, and then forget to dial them back up before I leave. I do have remote temperature reporting setup now, so basically I just want a lifeline when I'm away so that I can turn on some heat in the house if/when I get a notification that it's too cold. To do that, I probably only really need to rig up one or two heaters (not all 10.) Ideally, I would do it to all of them, but it sounds like this is getting expensive fast -- I think I could relegate one of the heaters to be that emergency heater that I don't touch the thermostat on and normally leave the power turned off. Then, if I get an emergency low temperature alert, I can kick that one heater into action. The house is basically one big open space, so heat will travel fairly well, at least enough to not let pipes freeze.

So, I think I'll start with automating just one heater and go from there. Since the heater wouldn't be turning on/off all the time, I think it would probably be safe to just wire it up to control the power to the whole heater.

 

[tmbrown97]

If you want to only start with one, I would strongly consider what Desert_AIP did - and using a communicating thermostat. Based on the cool-down fan cycling, I think automating the power to the unit seems like a bad idea. Just my $.02.

 

[mdesmarais]

Then, if I get an emergency low temperature alert, I can kick that one heater into action.

Not to be a stick in the mud anti-automation person, but. . . . . if all you are doing is keeping the pipes from freezing, why don't you just set one or two units at the low temperature that you are trying to protect against, and pull the knobs off. That is about the tightest control loop you can get- temperature drops too low, heaters kick on. Cut out the middleman, reduce possible failure points! Unless the thermostats don't go that low, I'd do that for sure.

If you do want to automate, I think there are several good methods in circulation above. Since all the heaters are in the same space, you could consider controlling all of them with a single external thermostat, if you did one of the relay methods. The benefit that I see to automation is that you can kick on the heat a couple hours before you arrive and be nice and warm.

 

[apostolakisl]

After looking at the wiring diagram, I don't exactly know what to make of the thermostat. It accepts both legs of the 220. The fan takes one leg before the thermostat, but the other leg is after the thermostat, meaning that the thermostat must control the fan. But then what is the FD? Fan delay? If this is what keeps the fan on while the element is hot, why does the fan need to have one leg wired after the thermostat if the FD device is what is turning it on?

 

[roussell]

After looking at the wiring diagram, I don't exactly know what to make of the thermostat. It accepts both legs of the 220. The fan takes one leg before the thermostat, but the other leg is after the thermostat, meaning that the thermostat must control the fan. But then what is the FD? Fan delay? If this is what keeps the fan on while the element is hot, why does the fan need to have one leg wired after the thermostat if the FD device is what is turning it on?

I noticed that too. The only thing that I can 'guess' is that it's a crappy design that only switches one leg on the 240 supply (the top in the schematic) leaves the bottom live to power the fan post-element-cut-off and also leave the dangerously circuit energized. It would be nice to know the rated motor voltage and poke around with a multimeter. I aslo noticed that the unit does come in a 120 volt version. That schematic would make slightly more sense if it were for 120V.

Terry