Electrical question (heaters)

[John Gregory]

We are remodeling our basement. We knocked down a wall and made two small bedrooms into one larger guest bedroom. In each of the two bedrooms I had an in wall 110V heater, each having their own thermostat. I wanted to use the two 100V heaters in the new larger room, but have one thermostat control both heaters. I purchased a line powered 220V thermostat and thought I could use one pair of wires for one heater and the other pair for the second heater. ( I have a separate 20amp breaker for each heater.) However I have found that this does not work. The 220V thermostat is meant for one device only. the L2(line) and T2(load) wires are always closed, so one heater runs constantly and does not cycle like the other one, wired to L1 and T1 does.
So my question is, is there a way that I can run both 110V heaters using just one thermostat?

Thanks. ( I have come to depend on the members of SMC as a source of information on any and all subjects. I am always in awe of the wealth of knowledge of this group)

[Kent Fitzgerald]

John, let me make sure I understand what you're proposing: You plan to run two independent 120V circuits (each with its own neutral) and use a single 'stat to interrupt both hots?

There are two-pole 240V thermostats that break both sides of the line, which I suppose would work, BUT I've never seen it done this way with two 120V circuits. Off the top of my head, I don't know if there's any specific code prohibition or safety hazard that would apply here, but it seems unconventional. Call me boring, but my rule of thumb in wiring is that I never want someone to look at my work later and say "never seen that before."

It also seems strange that the 'stat you have now has four connections (L1, L2, T1, T2), yet the L2-T2 is unswitched. In my experience, single pole 'stats only have two connections. Have you verified the operation with an ohmmeter (with the 'stat completely disconnected from the circuit)? Is it new or used?

[John Gregory]

I have verified with a meter, and I have tried two different brands of stats. both worked the same. On the old 110V stat there are only two wires, works much like a light switch. On the the 220V stat there are four wires, two red and two black, two are line and two are load. On a single 220V heater, you would only have to break one side to turn of the heater. I can do a bit of rewiring and run the heaters on their own stat. I just thought a single stat would nicer. The heaters are not for primary heat, the forced air furnance does that. During the remodel we insulated the walls and the need for the wall heater may or may not be needed.

Thanks for your comments.

[Kent Fitzgerald]

OK, mystery solved: I just looked up the 'stats I used at home (Honeywell CT62B) and found the following: "The CT62B model (DPST) makes double line break with the thermostat set to the OFF position" [my underline]. Presumably, in normal cycling it only breaks one side. Makes sense now.

If you're not sure you'll need the extra heat, I'd say just put in one of the heaters.

From balmy-until-this-week PA,
Kent

[John Gregory]

Thanks Kent,

I may have to just hook up one heater for now. and if a second one is needed, install a second tstat for that one.

[Mike Cutler]

John.
Umm..., I'm a little confused here. Do you have 240 or 115 supplying the thermostat? I'm going to call the Line Voltage Controller a "Thermostat" for the sake of discussion.
I have two AUBE TH-115, 7 day programmable Thermostats. These are pulse width modulating controllers. One of the thermostats is in the kitchen, and has two 240vac electric baseboard heaters connected to it. The other is in the living room and has four electric base board heaters connected to it.

You should, and I say this with hesitation, be able to put both of your heaters in parallel and then control the switched lead common to both, but I am still confused as to what the actual voltage is feeding the thermostat. If it is 240, and both heaters are 120 the heaters could be placed in series and controlled.
My hesitation is that the thermostat, and the heaters should be rated for the same voltage. If you are trying to control two seperate 120 loads off of a 220 fed Controler. I would caution against it. Electrically it can be done, but...

[John Gregory]

Mike,
I have two separate 110 circuits feeding the tstat. Each from a separate breaker. And I have two 110V in wall heaters in the large room.

I hope that information helps

[Kent Fitzgerald]

If it is 240, and both heaters are 120 the heaters could be placed in series and controlled.

From John's descripton, I take it these are fan-forced heaters. Wiring motor loads in series would not be a good idea.

[Rob Russell]

I'd say that separate t-stats would be a good idea - help eliminate hot spots in the room. Otherwise, you could use a regular low voltage t-stat to control a contactor that would power both heaters.

[Mike Cutler]

From John's descripton, I take it these are fan-forced heaters. Wiring motor loads in series would not be a good idea.

Theoretically it should work, as long as an equal voltage is dropped across both loads, But I still wouldn't do it myself. I'd have to see how the original enclosure wiring split the circuit(s)

John. If I am understanding you correctly. You have two seperate independent 120vac breakers connected to a single Thermostat device, in hopes of switching the hots to two seperate, and independent 115 heater assemblies. Is this correct? Electrically it can work. Aube makes a DPDT 240 Line controller, one of their TH-115 models, but... I cannot emphasize enough that you should not do this.
Two seperate, independent breakers feeding the same device, for which it wasn't, or may not be designed, is a little sketchy. There are certainely many appliances that have seperate independent breakers, My ASCO Dryer for one. It required a 220,and a 115 breaker, but it was designed for it.
My honest advice would be to combine the two 115 breakers into one 220 breaker at the box. Run the 220 to the thermostat controller, and connect per the manufactures diagram, and replace the two 115 heaters with appropiate sized 220 heater(s). Or find a dual zone thermostatic controller for 115 vac.
Electrically speaking it can be done, but it appears that you are maybe a little outside the box.

Here is a link to Aube's website. They may have something that will enable you to utilize your existing equipment.

http://www.aubethermostats.com/linevolt.htm

[Kent Fitzgerald]

Theoretically it should work, as long as an equal voltage is dropped across both loads,
Therein lies the problem. Motor loads are variable, and unless the two motors stay perfectly matched, they'll be dropping unequal voltages.

This might be a non-issue if the motor load is sufficiently small compared to the resistive load of the heat elements, but as you suggested, it;s not worth finding out.

[John Gregory]

Thanks all, I think I will just hook up one of the heaters for now. Maybe I will never need the second one, and if I do I will put it on a second tstat.
I respect your opinion and would not gerry-rig these heaters against your recommendation. Too much of a hazard. Thanks again for your help and expert advice.

[Carl Eyman]

Please, anyone, If what I suggest here doesn't make sense, say so. I'd consider wiring the two 110v heaters in series. and then wiring the thermostat in to the pair as though they are a 220v heater, For this is what they are in fact. I wish I had a program with which I could draw the scematic. But by way of further explanation, I'd wire one lead of one 110v heater to a 220v breaker, the other lead of this heater to the second heater, the other lead of the second heater through the thermostat, and back to the other side of the 220v breaker. The only caution is don't run a single conductor through a metal conduit.

My question is: why not leave the heaters and their thermostats alone? Let them cycle independently.