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Discussion Starter #1
I'm looking into upgrading my thermostat that is currently 2-pole being used to control heat from 2 heaters (fireplace and baseboard) on separate 240v breakers. The new one is a 1-pole that can handle 3800w max. Is it still possible to do this with heaters on separate breakers?

The thermostat manufacturer says yes.. the manufacturer for fireplace heater says they aren't sure.

Tstat company sent me attached diagram as recommended wiring for my setup.

Also attached is an estimation of how I THINK I have it currently wired..

How would I wire this for the new 1-pole thermostat, is their diagram correct, would that not cause any problems? The new one is made by Mysa

Thanks!
 

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You can use a relay (or definite purpose contactor) to detect power on one circuit and switch the load on another. That would keep the branch circuits separate.


https://www.ebay.com/itm/208-240VAC-Non-Reversing-Definite-Purpose-Contactor-2P-25A-SQUARE-D-8910DP22V09/331996678617?epid=11012070099&hash=item4d4c8b49d9:g:N9IAAOSwU1FaEt8K:sc:ShippingMethodExpress!60010!US!-1:rk:23:pf:0



Is the fireplace gas or electric? A flame switch would suggest gas but then why is it 240VAC? Confusing to me.






I did something like this with a 24VAC WiFi thermostat.



https://www.diychatroom.com/f18/baseboard-heaters-wifi-24v-thermostat-646459/
 

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Discussion Starter #4
I was concerned they weren't giving me good information because I kept repeating that the heaters were on separate breakers and seems like having two separate lines contacting each other would be bad right? So it's not possible to do this with a 1 pole thermostat? Can the two heaters be wired in the gang box so that they both use the same circuit? 20amp should be able to handle both..

You can use a relay (or definite purpose contactor) to detect power on one circuit and switch the load on another. That would keep the branch circuits separate.


Is the fireplace gas or electric? A flame switch would suggest gas but then why is it 240VAC? Confusing to me.
It's an electric fireplace the flame switch just switches the flame effect on/off which uses around 250w but isn't required for heat (flames stay on and off regardless of thermostat)
 

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Discussion Starter #5
NO. You need two poles, one for each breaker.
The diagram is for a two pole tstat.
The top diagram is one I just made to show how it is currently wired up with 2 pole.. the bottom is what the manufacturer sent me for using their 1-pole with 2 heaters.
 

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The bottom will not work with two separate circuits. It is drawn with one source in(top cable) and two heaters out(bottom two cables).
 

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Discussion Starter #7 (Edited)
The bottom will not work with two separate circuits. It is drawn with one source in(top cable) and two heaters out(bottom two cables).
I think one of the heaters has a separate connection to the breaker does that make a difference.. there's 6 wires in the box plus ground, currently 4 connected to tstat and 2 are capped off to each other

Possible to easily change the wiring to power both heaters from same source to have both controlled by tstat?
 

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You said two operate breakers, one 15 and one 20. To turn off two circuits you need two switches. That means a double pole thermostat.
I would not recommend creating any fancy circuits with relays. Just find a suitable two pole thermostat or two thermostats.
 

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Discussion Starter #9 (Edited)
Yeah the 2 pole I'm using now works fine but wanted to put in a smart thermo.. this new one called Mysa and they were insistent that it would work with my wiring. The heater maker also said it should work but I was still concerned so she said she'd consult with electrician and call me back.

Know of any "smart" 2 pole thermo that works with high voltage? The mysa one looked perfect aside from being 1 pole..

And when I asked about changing the wiring so that both heaters are on same breaker..?
 

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Discussion Starter #11
Fireplace heater uses 2700w max with flames on (15A breaker), baseboard is 1000w (20A breaker).. so it comes out just under the 3800w rating of the thermostat.
 

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Fireplace heater uses 2700w max with flames on (15A breaker), baseboard is 1000w (20A breaker).. so it comes out just under the 3800w rating of the thermostat.
There is a confusion here. You said 2 240volt breakers
2 breaker = 240 volts
1 double breaker= 240 volts
2 double breakers= no.:vs_cool:
 

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Mysa is a proportional electronic thermostat. That means it has control algorithms in it to control down to the cycle of the 60Hz. It uses a triac to control the load as mechanical contacts couldn't switch down to the cycle or partial cycle level.
..."Mysa uses a proportional control algorithm to heat the room. Mysa's proportional control algorithm can adjust the output of the heater to match the power that is required to maintain the setpoint. The current is regulated from 0 to 100%, increasing by 10% intervals. This is something a relay cannot achieve"...
For these reasons it can only control a single load on a single circuit. If you want to control two heaters on separate circuits you'll need two Mysa's....

You cannot use the relay approach I suggested earlier if the primary heater is controlled by a proportional thermostat.

After rereading the thread its not clear to me what is feeding your existing heaters. A 20A2P (240v) circuit and a 15A2P (240V) circuit? Or some sort of illegal 15A1P and 20A1P across phases to get 240V. Your initial diagram seems ambiguous.



If both of these heaters today are fed from a single 20A2P (240V) circuit then you should be able to use a single Mysa as it is rated for 3800 W and you have 3700W of load. You'll need to check that the fireplace is purely a resistive load and no electronics, motors or other things that wouldn't like to see a proportional fed power input.



Might be just easier to use two Mysas.
 

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Discussion Starter #16
Why not just run them both off the 20 amp breaker?
Yeah that's exactly what I was asking about haha.. but I think the fire one is already directly connected to the 15amp before it reaches the thermo.. so not sure that would work?

Also the heater company just called me and said she talked to her electrical engineer and he confirmed that I would have no problem connecting both circuits to the Mysa thermo so I am very confused.. you guys are saying no and they are saying yes. What would happen if I did that?
 

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Yeah that's exactly what I was asking about haha.. but I think the fire one is already directly connected to the 15amp before it reaches the thermo.. so not sure that would work?

Also the heater company just called me and said she talked to her electrical engineer and he confirmed that I would have no problem connecting both circuits to the Mysa thermo so I am very confused.. you guys are saying no and they are saying yes. What would happen if I did that?


Lets say you hooked them together what happens if the 20 amp gets turn off for some reason?
Just turn off and cap off the 15 amp breaker and wires.
 

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Discussion Starter #18
But the 15amp is connected directly behind the wall right so I don’t have access to that line to cap it off before it reaches that heater.. that’s how the flames work independently from the blower. Thermo people say that their device can replace a 2 pole and fireplace maker says I can combine circuits so I have no idea anymore
 

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But the 15amp is connected directly behind the wall right so I don’t have access to that line to cap it off before it reaches that heater.. that’s how the flames work independently from the blower. Thermo people say that their device can replace a 2 pole and fireplace maker says I can combine circuits so I have no idea anymore
If you have no access to the wire how did you think you could hook them both to the Tstat.
 

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Discussion Starter #20
The wires from the heater are in the gang box, but not directly from the 15amp breaker. There are 2 wires capped together there but I’m assuming they’re for the 20amp..
 
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