# Thermostat wire lenght for gas fireplace



## Highschoolhank (Jun 14, 2020)

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?


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## DAKSY (Jun 14, 2020)

20 -25 feet should work, but the spec for MAX T-Stat wire length & gauge, is probably in the install or owner's manual.


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## Highschoolhank (Jun 15, 2020)

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?


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## DAKSY (Jun 15, 2020)

Maybe. Your manual should also specify the correct type of T-Stat.


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## begreen (Jun 19, 2020)

Highschoolhank said:


> 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.


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## Highschoolhank (Jun 19, 2020)

begreen said:


> It looks like the thermostat will work for 24v and millivolt circuits.


Seems to tho nothing in manual.  Found another tstat I never used.  It's manual does say 24v or millivolt.  Now I have to  see if either works with the long run of wire.


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## begreen (Jun 19, 2020)

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.


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## Highschoolhank (Jun 20, 2020)

begreen said:


> 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.


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## Fingerlakes Fireplace (Jun 22, 2020)

Highschoolhank said:


> 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.


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## Highschoolhank (Jun 22, 2020)

Thanks for the input!  I'll update after I've tried various wire lengths and gauges, and thermostats.


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## Highschoolhank (Sep 26, 2020)

Thanks to all!  Finally got around to working on this and it's working with about 25 feet of 20 - 22 gauge wire.  Testing by just shorting the wires was a big help.


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