Activating Fans when a heater turns on

I have a very large 60amp heater in my garage that works great. Only problem is the ceiling is real high so I have a pair of fans that need to be turned on or all the heat hangs at the top of the ceiling.

I want to figure out how to automatically activate these fans when the heater come on and off. The fans are already on smart switches. Unfortunately this is a dumb heater hooked to what is basically a baseboard thermostat. I don't have any real way to interface with it.

I know there are devices that I can put around the power cord that will sense when current is flowing but I have never used one and I am unclear if anything will work with 240v 60amp. I do have access to the wiring fairly easy so if I needed to put a clamp around one of the hot wires that would be simple.

Anyone have any suggestions on something that might do the job?

A simple solution is a temp sensor. I used one on my gas fireplace at my last house. In the winter I had the fan reversed and would have it come on whenever the fireplace came on. I mounted the temp sensor on the mantel.

This of coarse depends on placement but anywhere close is probably going to see a quick upturn in temp. So it will probably turn it on pretty quick. Turning the fans turn off would be slower, but I imagine in a garage that wouldn't really be too big of an issue.

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Take a look at this...

Connect the coil side to the load side of whatever turns your heater on. Could be your thermostat or the main 240V contactor for the heater. Just use the appropriate wiring for the voltage. Connect the NO switch contacts to any device capable of handling a wired switch input (contact sensor, Zooz ZEN17, etc.). When the sensor sees the input closed, turn on the fans.

Second option is a whole home energy monitor with one input dedicated to the heater circuit. Great excuse to buy another cool gadget. :wink:

Option 3 is to check the control voltage at the thermostat. If it's 24VAC you have several options for a basic smart thermostat. There may be options available for 120VAC as well, but I'm not as familiar with those.

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Couple of solutions in here...The one with the current detection coil on one of your wires would work nicely and not really any messing about with the high amperage wires.


I don't have much time as I am running out the door for work but I wanted to thank you all for the great suggestions. I will look at each a little closer in a couple hours.

Thanks again.

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I second the option of the current transducer/switch on one of your heater wires as recommended by @chad.andrews, and connect it to a z-wave contact sensor like the Ecolink. Just be sure to put the current transducer around only one of the heater wires, not both of them. If you follow the post from @aaiyar, you will see a suggestion to use a split-core current transducer from Functional Devices.....that way you would not have to disconnect/reconnect the wire from the heater. Either current transducer will work.

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This is crucial advice when there are two 120V conductors of opposite polarity!!

Just one other thing. In this application, you need a split-core current transducer that can handle up up to 60A, which is the max pulled by your heater. The ones that I linked to in the other thread were limited to 40A.

Can I suggest this one from Amazon that handles 0-100A?


While my issue is triggering a blower fan to push cold air into the room where the wood stove is once the stove is up to temp, I'm going to look into this.

I do this very same thing with my wood stove in my kitchen. I have a motion sensor for the lighting there that has a temp function high in the ceiling, when it exceeds 26 deg. the fan puts a vacuum on the adjacent room and blows the cool air over the wood stove. Works well for circulation.


I ended up ordering both the smaller current switch from the article @chad.andrews referred me to and the bigger one @aaiyar linked to. They should be here tomorrow.

In my install it would be best if I can put the relay in the box with the thermostat. The stat wires in this application are 120volt and they are low amps. Not sure how many but it only calls for 16awg wire in the manual so I know its below what the little one can handle. If that works well it puts my contact sensor WAY closer to my hub so that's plan A. If not the bigger one will be on hand. I am sure I can find a good use for whichever I don't end up using.

Thanks again to all of you. I will post my results.

(Is it wrong that I am super excited!!!)


I am striking out on all fronts today. Hoping one of you who knows a little more than I do might be able to shed some light.

First I tried this guy

I took a reading off the Thermostat wire and it only draws 0.13 amps. So per the manual I wrapped the wire around a bunch of times (at first I did 9 and then got it up to 14). No matter what when I put my meter in the contacts I do not get a close. I saw some documentation that seemed to indicate that this switch needs an AC load and cannot be dry contact/DC but that would contradict what @aaiyar posted in the article linked above (I have the same zwave door sensor too). I am guessing there just isn't enough power to activate this thing off that stat.

Then I moved on to this guy

I put him around one of the Hot wires in the panel. My meter has continuity with the heater off but changes tone to almost a buzzing when the heater is powered on. It also jumps up to something like 56 ohms. The relay itself is also making a significant buzzing when power is on. I expected to lose continuity when the power came on.

Am I doing something wrong or did I just get a bum unit?

Thanks again.

I haven't actually used the second one. But am using the first one. I have the neutral for the 120V blower in my air handler passing through it, and it definitely closes the contact sensor.

I kind of assumed the second one would work the same way, but looking at it more carefully, it looks like it may not.


No worries - Glad I am not nuts.

I am thinking this one might work on my stat wire since it has a much lower requirement

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Yes, I agree. And cheaper than the first by quite a bit. Good thing Amazon takes returns!

Already packaged up and label printed :smiley:

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That 2nd unit is a sensor, not a switch. The more current that flows through the sensor the more voltage you will get on the output wires. That's why it didn't act like you expected it too.

Thank you - that makes better sense.

Thanks for that, our heat pump went out during the recent snow, but we were fine thanks to the wood stove. Some automation will help, because the manual blower gets forgotten if I am off doing something else. The automatic blower on the woodstove comes on at temp, but I need to delay the manual blower until the catalytic combustors kick in before I start forcing cold air into the room with the stove.

@Dredwolf1 Awesome, glad that helped. I too use a woodstove for when the power goes out and when it's on, lol. Love the wood heat.

I managed to finish this up tonight.

To summarize:
In my setup the thermostat wire only has .15 amps of current on it when the heater is running. The current switch linked below needs .2 amps to close the contact. Looping the stat wire through twice takes the current up high enough and it worked immediately. Then I used the Ecolink Door sensor because it has built in contact terminals.

A simple Hubitat rule now has my fans coming on 30 seconds after the heater kicks on and shutting off 30 seconds after it kicks off. Tested it a bunch tonight and worked flawlessly each time. Pic of my setup is included for clarity. Hope this helps the next person.

Thanks to everyone who gave me suggestions.