Help Needed: Adding Fan-Only Mode to Oil Furnace


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Old 04-11-22, 10:31 AM
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Help Needed: Adding Fan-Only Mode to Oil Furnace

Hello. I would like to add a fan only mode to my thermostat/furnace and need some help with the wiring. My equipment is as follows:

Thermostat: Nest Learning Thermostat 3rd Gen

Furnace: Comfort-Aire Patriot 80 Oil Furnace


Oil Primary Control: Honeywell R7284

My current wiring is 2-wire (red and white) from Nest RH and W1 directly to Oil Primary Control TT.

I do not have any air conditioning and likely wonít be adding it in the future (I live in a cold area). My Nest has been working happily for years without a C wire, so itís not a priority for me to add one if not necessary. The fan only mode is, however, a high priority. Iíve already run 18/5 Thermostat Wire but Iím not sure how to connect it.

I think the furnace and thermostat were previously connected through a fan center, but was later switched to a direct connection between the thermostat and oil primary.

Here's the fan center relay:
C | Y
R | G
| W

When I jumper between R and G, the fan turns on as expected.

Any help getting this figured out would be most appreciated! Thank you.
 

Last edited by PJmax; 04-11-22 at 12:45 PM. Reason: resized/labeled pics
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Old 04-11-22, 12:40 PM
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Welcome to the forums.

I think the furnace and thermostat were previously connected through a fan center, but was later switched to a direct connection between the thermostat and oil primary.
That doesn't sound right. It certainly doesn't match the diagram you posted.
You can't tie TT terminals to anything live. Your diagram shows an isolation relay which is 100% correct.

Are you sure your thermostat goes directly to the TT terminals ?
Technically we want to connect the nest to the fan center.
Then you'll have your needed C connection too.

At the fan center..... jump R to W. Do you hear a click from a relay ?
I labeled the iso relay wires. We want to verify that is working.
The burner should also start.
 
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Old 04-11-22, 01:04 PM
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That doesn't sound right.
I probably didn't explain it well (I'm a complete novice).

Here's a pic that will hopefully show it better than I can explain it:



The coiled wire dangling just below the fan center had been snipped and the new(er) coiled wire below it now runs to TT at the burner. I had traced the new coiled wire and thought it lead back to the thermostat, but perhaps I am mistaken.

I jumped R and W at the fan center and think I heard a click. There was a call for heat at the burner and it started as expected.

Thanks for the help! I've been trying to figure this out on my own as there's nobody in my area available to assist me with it.

 
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Old 04-12-22, 12:53 PM
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Sorry I missed your reply.

I jumped R and W at the fan center and think I heard a click. There was a call for heat at the burner and it started as expected.
Perfect. Exactly what we want. The remaining red and white wires connect to the isolation relay in the upper left of your picture as the diagram confirms.

Ok. Remove the two wire thermostat cable from the burner.
Using your new 5 wire cable connect directly to the fan center.
R -------> Rh
C -------> C
G -------> G
W ------> W1
Leave the 5th wire unconnected at both ends. Don't cut off.... just fold back.
 
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Old 04-12-22, 01:32 PM
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Ok. Remove the two wire thermostat cable from the burner.
Using your new 5 wire cable.....
R -------> Rh
C -------> C
G -------> G
W ------> W1
Leave the 5th wire unconnected at both ends. Don't cut off.... just fold back.
I can't wait to hook this up. I'll update once I get it wired (probably tomorrow). Thank you so much!
 
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Old 04-12-22, 01:50 PM
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I'll chime in with a follow up question -
One of my first projects asking DIY website was figuring out how to add a fan-on control to an existing forced hot air oil furnace.

One pleasant side effect was, although I don't have central air, setting the basic programmable thermostat to A/C-Fan Auto during warm spring & summer days really helped even out the temperature.
Later found that pulling the fan access panel in the basement and putting in a grill provided a workable "cool basement air" A/C effect that works well until August.

So, you MIGHT want to check through what happens if you simply need an auto-upper temperature for the fan to start circulating air though the house.
 
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Old 04-12-22, 03:39 PM
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You would set the thermostat to cooling. It would turn on the blower when the selected temp was set.

* Conventional one stage heating.
The default setting for fan control on the W1 wire is "Don’t activate" because most forced air heating systems will activate the fan automatically when the furnace (W1) is activated

Conventional one stage heating and one stage cooling.
Technically you want the conventional one stage setup but the blower may not activate if the A/C mode is selected. You may need to program for heating and cooling. It can be changed at any time later.
 
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Old 04-13-22, 10:11 AM
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Ok. Remove the two wire thermostat cable from the burner.
Using your new 5 wire cable connect directly to the fan center.
R -------> Rh
C -------> C
G -------> G
W ------> W1
Leave the 5th wire unconnected at both ends. Don't cut off.... just fold back.
Update: Everything is working perfectly! Thank you so much for the help.
 
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Old 04-14-22, 12:36 AM
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Good news and good job.
 
 

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