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Millivolt Gas Fireplace with 110v Fan - Just checking I won't ruin the Fireplace

Millivolt Gas Fireplace with 110v Fan - Just checking I won't ruin the Fireplace

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Old 02-01-18, 12:07 PM
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Question Millivolt Gas Fireplace with 110v Fan - Just checking I won't ruin the Fireplace

Hi all,
I want eliminate the need for a seperate on/off wall switch for the fan on my new fireplace I am having installed. The fireplace itself is millivolt controlled, but the seperate fan unit is regular 110v AC from what I can understand - here is a brief picture of the fan unit from the manual:

The HVAC/installer guy confirmed that a wall switch is the best way to control the fan and it can't be just directly wired into the thermostat.

I found this thread on here: https://www.doityourself.com/forum/t...ry-blower.html

I took note of the diagram (which I was able to get off of photobucket) and decided to follow this idea:


I plan to order the Orbit 83521 thermostat (which appears to be millivolt and 24v compatible) as well as the Honeywell R8285A1048 relay/transformer to control the fan.

My concern is that in the diagram, it shows the R and W wires going from that transformer into the burner. If the fireplace is millivolt, will that not send 24v to it and break it? Just want to make sure I don't ruin the fireplace. The guy who posted the question seemed to have no issues with the same setup but I really want to make sure this will work.

I am using a cheap thermostat for now but may throw on a Nest in future, I like the idea that this basically "upgrades" the millivolt control to 24V for wifi and better thermostats.

Thanks so much!
 
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Old 02-01-18, 01:23 PM
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With the Orbit thermostat you should be able to control the millivolt system with the R and W terminals with the RC and G going to the Honeywell. Removing the jumper between R and RC should keep any 24vac from the fireplace. Nest isn't supposed to be able to drive a millivolt but you could try the same thing with it.

Better for future flexibility would be to use a relay to isolate. Use something like https://www.amazon.com/Functional-De.../dp/B000LEUJU6 . Take the thermostat's W and Honeywell's C to drive the 24vac coil. Then take the common and N/O relay contacts to the millivolt system.
 
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Old 02-01-18, 01:53 PM
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Thanks for your reply! So it can be made safe from the 24v by removing the jumper, thats good to know. EDIT: I think I will just do it this way, sounds like it will work! Just to confirm:

W -> Fireplace W
R -> Fireplace R
R-RC <- Remove jumper here
RC -> Honeywell R
G -> Honeywell G
(nothing on Honeywell W)

That should definitely work? RC is for cool isn't it? but that will still trigger the fan in heat mode on the thermostat?
 

Last edited by canadajimmy; 02-01-18 at 02:10 PM.
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Old 02-01-18, 07:08 PM
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Yes.... Rc is for the cooling side and will work the blower (G) terminal.
However, the G terminal is not usually used in a heating system.

You will need to change the Fan Control Jumper to electric heat.
The G terminal will now work in heat mode.

The nest cannot directly run a millivolt system but can be used with a relay like astuff mentioned.
 
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Old 02-02-18, 11:36 AM
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Thanks for the help so far, really appreciate it. Interesting that that will work, but unfortunatly it doesn't sound like it will work with the Orbit 83521 thermostat.

According to their support it cannot do a blend of 24V and Millivolt. I posted a question on their site about it:

1. If I connect a 24V Fan control to RC and G, with R-RC disconnected (no jumper), will the fan still switch on when in heat mode? 2. Will the thermostat work with a 24V connection to RC/G and Millivolt connection (from fireplace) connected to R/W?

Unfortunately, this method will not work. Our system is only compatible with a millivolt system OR a 24VAC system. It not compatible with both together. Basically the millivolt system uses a low voltage DC power supply and the 24V fan system uses a higher voltage AC power supply.

Any suggestions on an affordable thermostat that can do this? I'm looking to buy on Amazon.com along with the Honeywell transformer/relay on there.
 
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Old 02-02-18, 12:23 PM
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Decided to call Honeywell support and ask them what was compatible with millivolt+24v simultaniously. They told me the following thermostats work with this setup:

RTH2300
RTH221
RTH111

Going to go ahead and get the Honeywell RTH2300, fingers crossed it will work!
 
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Old 02-02-18, 02:10 PM
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If the Orbit is not a battery powered stat then it will not work.
If it uses batteries.... I see no reason why it can't switch both.
 
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Old 02-07-18, 09:47 AM
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Hi guys!

I actually COMPLETELY changed direction with this project. What I really wanted was it to look nice on the wall, instead of having a separate fan switch, have it all on one thermostat. But then I realised, most thermostats only have "Auto" and "On" for fan control, but no "Off", which is what I want sometimes if I just want the fireplace to look nice without blasting air.

I used some off the shelf parts to assemble an all in one "panel" that has a 110v push button for the fan control, as well as a regular thermostat, all sitting on top of a nice 4 gang electrical panel to make it look coherent. Essentially creating a 110v/line voltage and millivolt combined thermostat panel.

I have posted a collection of photos from this project so far and will add more when it's mounted on the wall! I used a 4 Gang Decorator Faceplate, Honeywell RTH6360D Thermostat and Lutron Lyneo LX Push button switch.

The trick is that the 3 gaps on the right of the 4 gang faceplate are covered by the thermostat, with the thermostat wire coming through the middle gap of those 3. The first gap in the faceplate just covers the 1 gang box and has the 110v toggle switch in it.

Images here: https://imgur.com/a/UF9xU

I haven't mounted it on the wall yet, but will be adding more photos of that process when I do.
 

Last edited by canadajimmy; 02-07-18 at 10:52 AM.
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