Excellent replies guys, they were the kind of feedback I need....
The contacts in the thermostat might not handle the current. Remember, that when you halve the voltage, the current doubles to maintain the same number of watts. So, if the internal switches are designed for that lower current at 240vac, you'd burn it up at 120 since for the same number of watts, you need twice the current. Also, depending on how it is configured, the internal power supply may not provide the required voltages for the display. This is a question you should ask of Honeywell, or peruse the spec sheet carefully. For a general rule, you can always use a mechanical switch designed for higher voltages on a system with lower voltages. With an electronic device, the input voltages must be within the design specifications. Assuming this thing is electronic and gets line voltage, unless the specifications say 110, a 240v version won't work. Simple non-electronic switch, possibly.
That was the one thing I was really worried about - whether or not the electronic controls (and they are) could handle the difference.
I agree with your comment about current draw, but it looks like the specs say that both the 120V version and the 240V version (mine) draw a max. current of 15A, with the difference being the power rating: 1800W for the 120V, and 3600W for the 240V controls. If it was only that, then I'd not be
as concerned (I think...?)
However, the "proportional integral adaptive" controller (that's what they call it) they say is different than a regular electromechanical thermostat... apparently, to maintain the setpoint temperature, the controller looks at the amount of power required by the mat, apparently by percentage... it has 5 settings (0-20%, 20-40%, etc.). I wonder if it will be unable to achieve a higher setting, as maybe the most that the mat could generate would be 50% (i.e. 1800W, as opposed to the max. 3600W that the thermostat might expect).
Also, I use an Aube AF (air-floor) thermostat that has a floor sensor for high limit, then an air sensor to turn it on ... and that works great. Since your floor temp is always higher than room temp, not having an air sensor could result in a hot air temp in the room being fed even more by a floor that does not know the room is already too warm. An AF thermostat will keep the floor where you want it without letting it add excessive heat to the room (like if somebody had the sun lamp on for a while and the next person would like the room to cool a bit before washing up for dinner).
My understanding about these systems is that the heating zone is very limited in distance from the floor - the system heats the floor tiles only, and maybe a zone that extends only a few millimeters above the floor... as opposed to a radiant floor system, which is meant to heat the room as well... anyone know if this understanding is correct?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The mat is already installed, so all that's left is to connect the controller... I wonder if a test period would be sufficient to judge the effectiveness... or is there some hazard that I haven't considered...?
(I wouldn't expect a hazard, unless my mat tried to use more power than the thermostat could handle, but this is the opposite situation...)
Any additonal thoughts?