Last year I installed new digital 7 day programmable thermostats for all of our 220V baseboard heaters in our 10 year old house. We love them and have seen substantial energy savings as a result. We have always used the baseboard heaters as a back up system to come on when the airtight wood stove was not in use. Chimney cleaning yesterday required the wood stove to be allowed to burn itself out and the baseboards were turned up to heat the house. I could not get the 3 heaters controlled by one thermostat to heat up enough to warm the large room (open concept LR and kitchen approx 800 sq. Ft.) to acceptable temperature. Even tough I dialed in a temp of 24 oC, after 2 hours, the room remained at less than 20 oC (68 oF). Touching the heaters revealed that they were not hot, just barely warm, yet the thermostat should have been calling for max heat. Last night I set the temp to 21 oC, and retired for the night. This AM, the room was barely 17 oC. I turned off the breaker, a double 20 amp, and changed the thermostat to the old analogue one I had removed last year. The heaters came on and quickly raised the temp to 23 oC. I had successfully determined that the heaters were OK and the thermostat must be faulty.
Sorry for all of the above but I felt that I should explain the situation leading to my question. When I switched off the breaker to change out the thermostat, I noticed 2 worrying things:
1. The wires in the box behind the thermostat were warm to the touch. Is this something to be concerned about?
2. Before touching the wires to replace the thermostat, I tested them with a small hand held electricity sniffer, it flashes and squeaks when electricity is present, and it signaled power present on both of the black wires that attach to the thermostat. The red wires are ganged with a wire nut and are stuffed into the rear of the box. I checked again that the breaker was off, and indeed it was. I checked the operation of the tester and on another circuit and it operated as it should, squeaked/flashed when power on, no response to power off. Can offer guidance as to why there was power present when the breaker was off? Should I be calling an electrician?
Thanks,

Starchy,
I've had a few testers that operate in the vicinity of a live circuit... some performed better
Than others. I would have liked to test that circuit with a "Wiggy" which is one of most reliable testers
But which also requires that you "touch" live conductors for it to operate to see whether your tester was giving you a false reading.

You say the wires connected to the t-stat were "warm"... so I assume they were not "hot"? Typical conductors "NM" or "Romex" conductors are rated for operation at 60 to 75 degrees C which is hot enough not to be described as warm...
Dimmer switches as well as line voltage thermostats may heat up a bit (warm that is) during normal operation. Read the owners manual to see if that is described as normal by the manufacturer.

If the wires may be described as "hot" or you're concerned, a good electrician can meter the circuit load and the wiring to offer you a more conclusive opinion and identify any problems if there are any.

Thanks hfcarson,
I would say that the wires were only warm, certainly not hot. To be fair, the 3 baseboards controlled by this Tstat had been on full blast for about 2 hours, when I flipped the breaker off and removed it to install a replacement digital one. So I guess, from your answer, that it is OK for them to be warm. I think what I should do is remove the Tstat again, and put a volt-ohm meter across the wires to see how much current is actually present. My concern is how to connect the volt-ohm meter. I guess across the red and the black wires, on a 220V setting.
Thanks again for your response.

Starchy,
To measure the "current" you would likely need an ammeter, or "Amprobe". A volt-ohm meter might
be able to measure current or amperes but most likely it's only capable of safely reading one or
two amperes.

I assume these heaters are connected to a 20 ampere, two pole circuit breaker (written on the circuit breaker handle). If so, a good rule of thumb would be to limit the load or total current to 80% or 16 amperes on this circuit.

Do you know the rated wattage of each heater? If so, here is the math...
Let's assume each heater = (1200 watts x 3) = 3600 watts
Rated voltage = 240 volts
then total current: I = P / E
3600 / 240 = 15 amperes which is just under 80% and an acceptable load on a 20 ampere circuit.

I = amperes
P = power or watts
E = voltage

If you can't measure it, calculate it!

Thanks again hfcarson,
Not being an electrician, I have no idea what a two pole circuit breaker is. These 3 baseboards are wired into my 200 amp panel on two 20 amp breakers that have a bar that connects the two breakers' toggle switches together, much the same way all of the other baseboards are, as well as our electric stove and electric hot water tank. I think that it is wired as you described. As for the total wattage, I have no idea what it is. I will have to remove each heater from the wall to inspect the name plate for that info. I know the electrician who wired the house when we had it built in 2000, he is my neighbour, so I will contact him and have him inspect the wiring in the box for temp of the wires, but in the meantime, I will check the total wattage of the 3 heaters and report back with the calculation as you so kindly posted above. I will not be able to do this until early next week, but I will return to this thread and report.
Thanks again.