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electrifier, Master Electrician
Category: Electrical
Satisfied Customers: 1633
Experience:  Electrical contractor and electrical inspector for over 24 years with phone and networking expertise
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I need to replace my old thermostat for radiant ceiling heat.

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I need to replace my old thermostat for radiant ceiling heat. My old thermostat has red black and white wires going to it and is labled line load and common. All the thermostats that I find are for baseboard heaters and have only red and black wires. Will this type of thermostat work ?

Is your radiant celing heat 120 volts? Is there a neutral in the feed that supplies the radiant heat if it is 240 volts? Was the white wire connected? Does the old thermostat need 120 volts to work correctly or display correctly?

I will get you an answer with the answers to these questions. Thank you.

Customer: replied 8 years ago.

My radiant heat is 240 volts and the white wire is connected to the common screw

Does some part of the thermostat require this white wire to operate? Is the thermostat double pole? How many wires total are in the box with the thermostat? Is there 1 line and 1 load or 2 of each?

Customer: replied 8 years ago.
The thermostat has no screw for line 1, a screw for line 2 ,and 3 and 4 are marked load, but on the 4 screw the white is connected and says common on the mfg label. I'm not sure if I need a single pole or double pole
The thermostat you want to use for a replacement has 2 black and 2 red wires if I understand you correctly. This is so it can control a 240 volt circuit. You didn't tell me if there are additional wires in the box with the thermostat. You will only use one set of wires from the new thermostat. One is line and the other is load. Your new thermostat does not require a neutral/common connection so you willl cap that wire off so it doesn't cause any problems. This will allow the new thermostat to control your radiant heat in the same way as the old thermostat did.
electrifier and other Electrical Specialists are ready to help you
Customer: replied 8 years ago.

1 set of wires to box from breakers are black white and ground. the black wire goes directly to line on old thermostat the white is tied to one red going to heater. the other red wire from heater goes directly to load. I've got a new double pole thermostat. Do I tie the hot black with the 2 blacks on thermostat and tie the 2 reds on thermostat with single red in box and then cap off the white

Customer: replied 8 years ago.
Relist: I still need help.

I just arrived home. We can continue to get your solution here. There is no need to relist.

Now I understand your wiring. The white wire is not a common or neutral wire. The white and the black are the 240 volt lines. These 2 wires need to connect to the two line terminals. The black and red wires from the heater will connect to the 2 load terminals. This will properly disconnect the entire electrical circuit from the heater. Your documentation that came with the thermostat will tell you which is line and which is load so you don't make a mistake. The white wire, by code, is supposed to be identified with black at each termination when it is used as a power wire like this. This will assure nobody will mistake it as a neutral and get hurt by it.

Customer: replied 8 years ago.
I'm still confused. The two wires coming from the heater are both red, not black and red. One is tied to the white from the circuit. The new thermostat has one black labled L1 and one labled T1.
The red wires are labled L2 and T2. It doesn't say which is line or load.
L1 and L2 are line while T1 and T2 are load. The 2 red wires from the heater connect to the load side. The black and the white maked black go to L1 and L2.
electrifier and other Electrical Specialists are ready to help you
Customer: replied 8 years ago.
I think that did it. thanks alot!
If anything else comes up please feel free to contact me. If it's on this topic come here and it will be no more charge. I've enjoyed working with you.

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