Thermostat amp rating for ceiling radiant heat

lagrunion

Hi everybody,



I would like to buy a replacement thermostat for the ceiling radiant heat in my 1972-built apartment (just moved in). But, I’m not sure what specs to look for because I’m not knowledgeable about electrical matters.



My old thermostat is a GE (Model 3AHT40A1B2). It is labeled: non-inductive; 120/240V A-C, 22.0 AMP; 277 VOLT A-C, 18.0 AMP. It is connected by two wires, red and black. The corresponding circuit breaker consists of two switches numbered “20” on each (tied together).



My question is: What specs must I look for in choosing the right thermostat?



I prefer a digital thermostat, but I can’t find any with the same specs. They all seem to have a lower amp rating than my old GE thermostat.



For example, I looked at the Honeywell RLV430, which says it cannot be used with a resistive load over 14.6 A. I don’t know the resistive load of my heater, so can I still use the RLV430? Or would that be dangerous?



Thanks!

icesailor

Radiant electric thermostat.

Call a Pro.

You break it, you own it.

Mark Eatherton

Said slightly differently from Icesailor...

The system to which you reference is a high voltage system, probably 240 volts, 20 amps. The actual amperage is dependent upon how the panels were wired. You need to have a pro measure the resistance of the circuit to determine the amp draw per grid. Not a job for the faint hearted or inexperienced. It also requires instrumentation not usually found in the typical weekend warriors tool bucket.



A programmable thermostat could be installed, but would be very difficult, because no one makes a line voltage programmable thermostat that I am aware of, and it would require having to set a relay/transformer package, and the existing wiring scheme is not conducive to that.



One of the biggest complaints from this type of system is the Hot Head syndrome. It is due to the fact that the emitting surface is either ON or OFF, and has no means of being anywhere in between. If there were some way to put your radiant ceiling into an outdoor reset mode, then you would be much more comfortable for any given situation. You have an air sensing thermostat controlling a radiant heating system ,and until the room gets close to set point and starts cycling, you will be uncomfortably warm.



It's a matter of control.... And unless you are comfortable working with high voltage stuff and have the proper equipment, it is probably best that you contact a qualified electrician to determine your needs and assist you in chosing a thermostat, but things haven't changed much in that area in the last 40 years, so you might not be happy with the end results...



At a minimum, you must match the amperage of the existing thermostats. But again, you will end up with an ON/OFF switch that isn't going to change the operating characteristics of the radiant ceiling.



HTH



ME

lagrunion

Thanks

Thank you, Mark, for your detailed response. I plan to forget about getting a digital one, and just put in a mechanical one. I have found a couple of mechanical thermostats with specs same as my old GE one.

lagrunion

Installing a single pole, mechanical thermostat

So I got the Lux LV1 single pole thermostat with ratings (22 amps @ 125 VAC, 22 amps @ 250/277 VAC) that match/exceed the old GE thermostat.



I removed the old one, and noticed that tags on the wires coming out of the box say: GE, HW1120C1, 1200 W, 240V. I assume these are the specs for the radiant heat.



The LV1’s manual says to connect the line wire to the top screw on the thermostat and the load wire to the bottom screw.



I have two wires that connected to the old GE thermostat: red and orange. I used a multimeter to test them, and they both turned out to be hot (readings around 115). That confused me, because I thought only the line wire was supposed to be hot, and the load wire was supposed to be neutral. Is this a problem?



So my questions is: Since I can’t tell which wires are line versus load, does it matter how I connect them to the LV1? In other words, is it ok if the connections are reversed?



Thanks!

Mike Kusiak_2

Line to line voltage

If the heating element is running on 240 VAC, then both conductors are hot to ground. Each conductor should measure 120 VAC to ground, but 240 VAC between the two wires. If the thermostat manufacturer really wants you to connect the load to a specific terminal, then you will have to trace the wiring back to the heater to see which wire is actually connected to it.



I can't think of any reason why it would matter if the connections were reversed, but if the manufacturer specifies a certain connection I would be inclined to follow their directions.

VictoriaEnergy

***IMPORTANT****

If you have Flexwatt or Flexel brand in ceiling radiant heat panels disconnect them.  The certification was revoked due to overheating and subsequent structural fires.  Flexwatt was one of the dominant suppliers of this product during the mid 80s to mid 90s. 



If you don't know what you have, turn power off at the panel, go into the attic and check.  Be very careful not to get ANY insulation under the panels



Most other suppliers (Therma-Ray) specked a low differential thermostat to be used with them.  White-Rodgers had one with a 0.4 deg F differential 20A @240VAC.  Standard stats sometimes will cause cracking issues to develop in the drywall near the panels.

lagrunion

Thanks

Thank you Mike and VictoriaEnergy for your advice!