Wiring smart thermostat to Oil-O-Matic furnace.

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Old 11-02-20, 10:52 PM
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Wiring smart thermostat to Oil-O-Matic furnace.

First ever experience with an oil furnace found in an older (1947) home we just purchased. It's been well serviced and has a lot of life left in it so no reason to upgrade anytime soon. With that said, my wife purchased a smart Nest thermostat to help bring the home into the 21st century.

I'm pretty handy, but have little experience with low voltage and heating. I'd like to get this hooked up, control the heat and also control the fan independently from the furnace, to circulate air throughout the home with / without the burner running.

I'm not sure if my current setup will allow this. If not, I'm open to picking up / swapping out existing parts if it's not too much extra cost.

What I know so far:
- 15A - 120v dedicated to furnace and fan.
- There's only two wires running to the current thermostat (Honeywell RTH221B1021).
- The burner controller is a Honeywell R8184G4009. It has two 'T' terminals and two 'F' terminals.
- The two 'T' terminals are running to the thermostat and the two 'F' terminals are running into the transformer / igniter.
- There's a 'Fan' and a 'Burner' 120v switch on the side of the furnace. The burner switch is always up, and kicks on with the thermostat controls.
- The fan can be manually powered on with the switch (independently from the burner). Also if left in the down / off position, it will kick on periodically when the burner runs.
- Fan is probably original. It's a Jack and Heintz (JAHCO) 1/4 HP belt driven motor.
Thanks!
Hendrix








 

Last edited by PJmax; 11-16-20 at 11:59 AM. Reason: resized pics/labeled one
  #2  
Old 11-02-20, 11:47 PM
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Welcome to the forums.

You cannot connect a nest thermostat directly to the TT terminals.
The nest as with most other thermostats requires 24vAC to operate.

I would recommend getting a fan center and an additional 24v relay. The fan center supplies 24v for the nest and has an onboard relay that could be used to control the blower. You'd need the additional relay to connect the thermostat to the TT terminals.

Fan center
24v relay

If you didn't want to remotely control the blower..... you could use just the fan center.
The links are examples. There are others on those pages that will also work.
The wiring is fairly easy and we can help you with that.
 

Last edited by PJmax; 11-03-20 at 05:40 PM. Reason: link fixed
  #3  
Old 11-03-20, 11:24 AM
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PJ thanks for the quick response and info!

That sounds like something I should definitely be able to handle. Could you provide another link to the 'Fan center', the link above didn't redirect anywhere.

Thanks
Hendrix
 
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Old 11-03-20, 05:36 PM
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Hi, here is a link to the fan center.
This maybe a better choice
https://s3.amazonaws.com/s3.supplyho...48-Install.pdf
Geo🇺🇸
 

Last edited by Geochurchi; 11-03-20 at 05:48 PM. Reason: Changed link
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Old 11-03-20, 05:41 PM
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Thanks Geo ....... My link fixed too.

Although they are two different units.... they both do the same thing.
 
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Old 11-03-20, 07:36 PM
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Kudos to you both!

I'll check these out and pull the trigger on something this weekend.

Be back shortly to log the processor and pick your brains on how to wire them up!

Thanks
Hendrix
 
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Old 11-04-20, 05:18 PM
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That furnace reminds me of the one in my grandma's house when I was a kid. Strong as a tank, and will run forever. Just be sure that the heat exchanger is solid and shows no leaks, as carbon monoxide poisoning is very dangerous. Also, the lock nut appears to be off at the motor on the electrical feed to the motor.
Andy

 
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Old 11-16-20, 09:18 AM
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Andrew Thanks for the heads up. Once this is wired up, I'll be scheduling a fill up to get us through winter and a service inspection. We have the logs and it looks like the previous owner was on top of maintenance and had regular inspections done.

Parts have arrive though. I picked up both of PJ's recommendations. Does anyone have a wiring diagram they could send over for this setup?

Fan Control: White-Rodgers 90-113 SPDT Control (link)
Relay: Emerson 90 380 Relay 24V (link)

I have 120v going into the system. It splits at a junction box, and runs 120 to the fan motor and 120 to the burner area. I haven't been able to dig into the wiring near the burner area much, but I can snap some more photos if needed.

Thanks
Hendix
 
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Old 11-16-20, 12:07 PM
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I resized and labeled one of your pics. That's the fan/limit switch. It looks like your mechanical switch overrides that. I need to see that wiring to advise you in connecting to the fan center.

If the blower works just fine and automatically with the switch down..... just connect the black and red wires from the fan center across that switch or in place of that switch. No polarity. The brown NC wire is capped off. Activating the FAN ON from the stat will activate the fan center and turn the blower on.

The fan center gets 120v always live on the 120v black and white wires.

The relay has four connections.
It gets W and C from the fan center on 1 and 3 - no polarity.
It connects to the TT terminals on 2 and 4 - no polarity.

 
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Old 11-16-20, 02:32 PM
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Hey PJ - Thanks for the diagram.

I'll have to double check the fan automation. I may have jumped the gun and assumed it kicks on with the 120v switched to off/down. I've tried multiple times to run the burner without the fan switched on today. The fan wouldn't turn on and I noticed that the burner will turn off automatically pretty quickly (within 10-15 mins). Assuming that's for safety or an internal switch that turns it off if it's too hot?

The house doesn't get nearly as warm without the fan on, and realizing the burner turns itself off within a matter of minutes, having the fan come on automatically when the burner turns on is definitely a priority now as well.

Thanks
Hendrix
 
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Old 11-16-20, 02:36 PM
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You will have to figure out how the blower works. It is supposed to be controlled directly from the fan/limit control. When the heat exchanger gets warm.... it turns the blower on. The manual switch is supposed to bypass the fan/limit switch and keep the blower running continuously while in the up position.
 
  #12  
Old 11-17-20, 06:18 AM
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Hi, that switch that’s on the Fan limit is likely an ON/AUTO switch, On would be fan running constantly, is that correct? It would seem that the switch marked fan on that 2 gang box would only shut the fan OFF.
Geo 🇺🇸
 
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Old 11-17-20, 03:25 PM
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You need to tell us more about that switch. You should have a fan/limit control that cycles the blower on plenum heat.

If it turns out that is not the case or it is defective.... you can wire the fan center wires to always control the blower.
When the thermostat gets programmed.... you set the blower to electric heat. That means the blower turns on and off based on a call for heat.
 
  #14  
Old 11-21-20, 09:34 PM
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I found a toggle switch on the fan limit, which I must have accidentally flipped off, because I was finally able to verify that the fan does in fact kick on with the fan limit. The wiring is a bit confusing, but I mapped it all out which I hope helps.

I may have flip-flopped the wiring on the fan-limit switch in my diagram. The wires run through small conduit and I couldn't tell if the wires were running to the top or bottom terminals.

Also sorry about the image orientation, it auto rotated them after upload.
















 

Last edited by hendrix; 11-21-20 at 09:53 PM.
  #15  
Old 11-22-20, 05:29 AM
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Hi, what model Tstat do you have, does it allow Fan On/Auto? Sounds like you are trying to run the fan only from the Stat ,correct? The Dia. that Pete posted will work perfectly, remove the current wires from the burner control TT and connect 2 wires from 2 - 4 on the relay there, power the Fan center from the load side of the service switch or at the primary control, which ever is easiest, remove the toggle switch from the fan limit and connect the Red and Black in its place.
Geo 🇺🇸
 

Last edited by Geochurchi; 11-22-20 at 05:57 AM.
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Old 11-22-20, 10:41 AM
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It's a Google Nest model A0013. It's their 3rd gen learning thermostat and I believe it does allow for independent fan control.

Here's what I found on it: https://support.google.com/googlenes.../9296419?hl=en
 
  #17  
Old 11-22-20, 10:55 AM
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Hi, that seems like it should work fine if wired as we described.
Geo 🇺🇸
 
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Old 11-22-20, 11:21 PM
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Not sure what all the confusion is.

My diagram shows you four wires between the fan center and the thermostat.
The relay clearly shows the TT connections.
At the fan limit switch.... remove that toggle switch and connect the red and black wires from the fan center in its place. The two wires that connect to the left side of the fan limit switch are also in the splice box and you can connect there.
 
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Old 11-25-20, 12:38 AM
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You guys are great. I'm new to all this, so thanks again for all the info and patience.

I got everything wired up, but haven't tried to power anything on yet. I wanted to confirm the current setup before I turn it on and something shorts out.

I think I'm missing something here, I'm not sure if I have the red/black mixed up and also not sure where to get power to the actual fan control. If I'm connecting the red and black wires to the left side of the fan/limit switch:

Top (Line): Power from circuit breaker + Black wire from fan control.
Bottom (Load): Power to Fan + Red wire from fan control.

In theory I should be able to also power the fan control from the top terminal as well on the left side?

Thanks
Hendrix


 
  #20  
Old 11-25-20, 06:10 AM
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Hi, Black wire with ? Should connect to the load side of that service switch, White wire should also connect to the neutrals in that same box.
Geo 🇺🇸
 
  #21  
Old 12-23-20, 04:07 PM
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Installation update. Thanks for all the help, the thermostat has been in for about 3 weeks and is working great!


 
  #22  
Old 12-23-20, 08:25 PM
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Nice job.

However there is a change that should be made. 120v wiring/splices are supposed to be contained within an approved splice box. The fan center is designed to install directly on the front of a 4" square (1900) box.

 
 

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