I'm a little confused, the heater has a wall thermostat how did you turn it on "manually." If you used a thermostat/control knob on the unit, something is wired incorrectly. You need one or the other, not both.

There is no thermostat or control knob on the actual heater. All of the thermostats have had a manual dial like the ones shown in my two links above. The wall thermostat there now does nothing. By "manual", I mean that the previous ones have worked but only as on/off switches. Instead of being able to set it to say, 65 degrees and have the thermostat turn on the heater if it got below 65 and turn the heater off if it got above 65, the thermostat would just turn the heater on and off and not modulate the temperature. I could hear it click when I turned the dial past the "off" part but then it was full blast heat and would not automatically turn off no matter how high the temperature got. So I might set it before bedtime to 60 or 65 degrees and wake up the next morning to find the temperature was over 80 degrees (ETA - And the heat would still be on). I hope this description makes sense. Let me know if it doesn't.

Is the thermostat mounted on an outside wall? Typically that will cause a thermostat to call for more heat than it should. If the wall is poorly insulated, it might keep the thermostat so cool that it doesn't respond to room temperature until the room is very warm.

No, it's an inside wall.

ETA -The same thing happens with any temperature, really. Set to 50 degrees or even lower, it just never turns the heater off.

Now that I think about it, we have a similar set up in a rental house and that type of thermostat works perfectly there. You can hear them click on if you set them above the current temperature and they turn the heat off if you set them below the current temp. I am not sure why we have always had problems at our condo. I have read that those cheap thermostats have a fairly high failure rate and I was hoping that was the problem, but I'm now thinking that it's probably something else.

Thanks, DavidR! You've given me a lot of helpful information. I will try to get this sorted out this weekend.

Duh. Why didn't I think of this above? It just occurred to me that on a plain mechanical thermostat, you should be able to connect BOTH Line 1 and Line 2 to the power in wire, and then connect both Load 1 and Load 2 to the wall wire that goes to the heater.

"There are two wires to hook the thermostat up to and it seems like this should all be pretty easy."

If you only have two wires, then this must be a 120 V circuit. Here is the wiring diagram for the thermostat you bought:

If you bought the CT410A you connect the two wires as shown on the left. This thermostat has no on off switch. If you bought the CT410B then you would only use two wire connections (L1 and T1). That connection is controlled by the temperature setting. If you wired it using L2 and T2 then is works only as an on off switch.

You could use the CT410B with your two wires and wire in L2 and T2 as the on off switch. The connection would be as follows:

Hot wire -> L2, T2 -> L1, T1 -> heater

This would allow you to turn off the heater in the summer when you don't need it.

Before you connect the thermostat, you can connect the two wires to themselves to verify the heater turns on. If it does not then you have a wiring problem. Make sure you are turning off the breaker when you are doing the wiring.

"f you only have two wires, then this must be a 120 V circuit."

Could you explain why? I see no reason it can't be a 240 volt circuit. A 240 volt baseboard heater doesn't need a neutral.

It's unusual to see a 120 volt baseboard unit except in a small bathroom. Those are often 750 watt heaters.

Maybe I'm missing something.

I agree there is no neutral. However in a residential house the 240 V is created by 120 V which are 180 degrees out of phase. The load (heater) has to be connected between the two 120 V hot wires. That's why the 240 V line thermostats have four wires.

I suppose someone could have wired one to the 120 V legs to the heater and installed a single pole thermostat on the other 120 V leg. Electrically it would work, but a very bad practice and probably violates the electric code.

A 120 V electric baseboard heaters are rated up to 1250 W. They are unusual for a wired installation.

Now I'm confused. I believe there are 4 wires to connect the electric baseboard heater and 2 wires to connect the wall thermostat. I looked at Menards.com and I see that they have both a 120V and a 240V heater. I am not sure which one we bought as a replacement, but I should be able to find out tomorrow.

Is one of these safer than the other considering my wiring? Both say 1500 W.

120 V Heater

240 V Heater

I'm not sure what 'safe' means in this context. They are basically both the same.

For the 240v unit, the thermostat 'breaks' both hot wires when off. For the 120v unit, the thermostat breaks the single hot when off, the neutral is not switched.

I am not sure either, weedmeister. I am just wondering about mike_home's comments regarding safety.

You need to buy the heater that is compatible to your circuit. Wiring a 120 V heater to a 240 V circuit will cause it to over heat and cause a fire. Wiring a 240 V heater to a 120 V circuit will produce a quarter of the rated heat.

I think you have a 120 V circuit, but I can't be sure. Homeowners get creative when they do electric wiring, so anything is possible. You need to figure this out before you do anything. I don't feel good giving you guidance without knowing how this circuit is actually wired.

I appreciate your concern, mike_home. I found the box (hadn't recycled it yet) and the heater is 240 V. How do I figure out the voltage of the circuit? Can I go by the number of wires or do I need a meter?

Look at the circuit breaker box. You should see mostly narrow width circuit breakers which are for 120 V circuits. A 240 V circuit breaker would be twice the width. Check the circuit breaker that is wired to the thermostat and heater. Make note of the amp rating.

Let's clear up a few things.

Last time I checked, it was still code-acceptable under some circumstances to use a single pole thermostat to control a 240 volt heater, opening only one hot lead. I don't think it's a good idea, but it's sometimes (maybe often) done.

A 240 volt circuit is not 2-phase power. The neutral you use for 120 volts in a 240 volt supply is simply a center tap in the pole transformer. The two halves are in phase; otherwise you couldn't get 240 volts.

In the case of a heater, the 240 volt supply could go to the heater with a 2-wire switch loop to the thermostat. I personally wouldn't wire it that way, but I've seen it done.

A 240 volt heater fed by 120 volts will use half the current and produce 1/4 the normal output, not 1/2. That's Ohm's law. Power (which is what makes the heat) is proportional to the square of the voltage. P=E^2/R, where P is power, E is voltage, and R is resistance. R is the heater's resistance and it's obviously fixed.

A 120 volt heater given 240 volts will use 2 times the current and try to produce 4 times the heat output. If you're lucky, the heater will just stop working. It may get very hot and/or go bang. Do not do this.

A quick check for voltage is, as Mike said, to look at the breaker, but be careful. Not all double width breakers are 240 volt.

Many GE panels can use a mix of 1/2" and 1" single pole breakers, and 1" and 2" double pole breakers. So you could have 1" 120 volt breakers and 1" 240 volt breakers in a GE panel, though I don't know how likely that is.

Other panels use double width breakers that can be tandems (two 120 volt breakers in one).

A handle that looks like 2 handles linked together is a pretty certain sign of a 2-pole, 240 volt breaker.

A sure way to tell is to use a voltmeter on the live circuit (be careful). Last I saw, crummy-but-accurate-enough digital multimeters (DMMs) were under $10 at the cheap tool place (you know the one I mean). They even sometimes give them away with any purchase.

My bad about saying that going from 240 V to 120 V produces half the heat output. DavidR is correct that it is a quarter.

I don't understand how you can produce a potential difference of 240 V across two 120 V potentials that are in phase. If they are both in phase then the voltage difference between the two would be zero.

"If they are both in phase then the voltage difference between the two would be zero."

But you're not taking the difference! With a center tapped transformer winding, which is precisely how a domestic 120/240 volt service is implemented, the two halves are in series and in phase. The voltage across both halves (the full transformer winding) is therefore the sum, not the difference, of the halves' voltages.

To see this in practice, find a standard power transformer with two totally separate secondary windings of different voltages -- for example, 180 volts and 6.3 volts. Connect the windings in series and measure the voltage. Then reverse the connections to either winding and measure again. One way (in phase, boost) you'll measure 186.3 volts, the other way (out of phase, buck) you'll read 173.7 volts.

Here is a video that does a great job of explaining the relationship of 120 V and 240 V service in a residential home:

Using an Oscilloscope to Understand 120 VAC Split phase Household Power Supplies

It is a bit long (11:44) but well done. Its great to watch somebody who knows how to use both a voltmeter and an oscilloscope and can explain the differences.

"With a center tapped transformer winding, which is precisely how a domestic 120/240 volt service is implemented, the two halves are in series and in phase."

No and No. Not in series and not in phase.

"The voltage across both halves (the full transformer winding) is therefore the sum, not the difference, of the halves' voltages. "

Not when measured from ground (or neutral).

Sorry I have not been back to update this thread. I was wrong about the number of wires for the thermostat (miscommunication between my husband and myself). I will try to get a picture tomorrow.

Unfortunately, nothing was marked in our breaker box when we moved in and we haven't rectified that. We just turn off every single breaker when trying to wire anything and rely on daylight and flashlights.