Thermostat wire lenght for gas fireplace

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Highschoolhank

New Member
Jun 14, 2020
6
Upstate New York
I have a Majestic DV360 gas fireplace, close to 20 years old. When I moved in I replaced the regular on/off wall switch with an old (20 years also) Robertshaw 9600 programmable thermostat to give a bit more control of the fireplace. There is probably 6-7 feet of wire between the gas valve terminals and the thermostat.
Because it is so close to the fireplace the heat has more affect on the thermostat than I would like so I want to move the thermostat farther away. Although this thermostat is low voltage (but apparently not millivolt) so far it has worked OK to open/close the gas valve as desired. Moving the thermostat would require a wire length of anywhere from 25 to 50 feet. Would you expect that with the additional wire length the thermostat would still operate the gas valve? If not, would a true millivolt thermostat do the trick?
 

DAKSY

Full Time RVer
Staff member
Dec 2, 2008
9,076
Wherever we're parked
20 -25 feet should work, but the spec for MAX T-Stat wire length & gauge, is probably in the install or owner's manual.
 

Highschoolhank

New Member
Jun 14, 2020
6
Upstate New York
Thanks for the quick reply. Did not find anything in the manual about wire gauge or length but I can try different things without actually routing the wire. The tstat being for 24v, am I just lucky that it works with the 750mv gas valve?
 

begreen

Mooderator
Staff member
Nov 18, 2005
90,419
South Puget Sound, WA
Thanks for the quick reply. Did not find anything in the manual about wire gauge or length but I can try different things without actually routing the wire. The tstat being for 24v, am I just lucky that it works with the 750mv gas valve?
It looks like the thermostat will work for 24v and millivolt circuits.
 

begreen

Mooderator
Staff member
Nov 18, 2005
90,419
South Puget Sound, WA
Millivolt just needs continuity between the two wires. You don't need a thermostat to test, just temporarily short out the two wires at the end of the run by wire nutting them together. If the burner lights, then the properly connected thermostat will do the same thing.
 

Highschoolhank

New Member
Jun 14, 2020
6
Upstate New York
Millivolt just needs continuity between the two wires. You don't need a thermostat to test, just temporarily short out the two wires at the end of the run by wire nutting them together. If the burner lights, then the properly connected thermostat will do the same thing.
Thanks for the tip. I have about 25 feet of wire I'll try it with hopefully next week.
 
Jan 9, 2017
139
Upstate NY
I have a Majestic DV360 gas fireplace, close to 20 years old. When I moved in I replaced the regular on/off wall switch with an old (20 years also) Robertshaw 9600 programmable thermostat to give a bit more control of the fireplace. There is probably 6-7 feet of wire between the gas valve terminals and the thermostat.
Because it is so close to the fireplace the heat has more affect on the thermostat than I would like so I want to move the thermostat farther away. Although this thermostat is low voltage (but apparently not millivolt) so far it has worked OK to open/close the gas valve as desired. Moving the thermostat would require a wire length of anywhere from 25 to 50 feet. Would you expect that with the additional wire length the thermostat would still operate the gas valve? If not, would a true millivolt thermostat do the trick?
[/QUOT It is all about resistance of the circuit. And also the health/output of your thermo-pile. I would use 18 gauge wire for that application. the larger wire will have less resistance.

millivolt thermostat are just like a switch, that have lower resistance then 24 volt thermostats. you may have just been lucky so far, as some 24 volt thermostats have low enough resistance to work for millivolt.