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I’ve been searching for way too long for the doorbell transformer in our house (I suspect it’s not putting quite enough juice for a Nest Hello doorbell setup as the Nest Hello works but the chime doesn’t sound because the solenoid moves but not as much as it needs to).

Anyway, I’ve been looking for this doorbell transformer in all the typical places, such as behind the chime or the button, in the circuit breaker panels, garage, closets, attic, crawl space, etc. and not finding it.

The one thing I found that looks like a transformer is on top of a galvanized metal switch in the closet with the furnace (Trane XL-80 gas furnace). I was guessing that it was a furnace transformer, but is it possible that this is the doorbell transformer?!

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Update: What is this?

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  • Are furnace transformers typically inside the furnace? Because if so, then maybe what I found is the doorbell transformer? Dec 29, 2018 at 2:39
  • Ok thanks for confirming that’s a furnace transformer. Dec 29, 2018 at 3:14
  • Look on the side of the light fixture boxes in your basement/attic
    – noybman
    Dec 29, 2018 at 3:32
  • Would an endoscope or a tone tracer help me find the doorbell transformer? Dec 29, 2018 at 3:42
  • In one 1950s era house we finally discovered a single transformer powered both the furnace and the doorbell.
    – Tyson
    Dec 29, 2018 at 12:50

5 Answers 5

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Your pic is a furnace transformer. A furnace transformer will be located close to the furnace and in most cases is mounted to the furnace itself. Doorbell transformers are a different story. I've found them in walls, behind the chime. I've also found them in the attic as well as the basement or crawlspace.

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  • In our HVAC closet there is a transformer on the drywall next to the furnace. I always thought this was the doorbell transformer and the HVAC transformer was inside case of the natural gas furnace HVAC . It is 102 F outside right now and I don't want to do anything to make the a/c go down. I don't have a current clamp and I am trying to figure a way to test without disconnecting anything. Jul 13, 2023 at 21:34
  • I clipped my Fluke 115 in V a/c mode to the exposed contacts of the transformer: reading 20.2 V. Had a family member ring the doorbell: reading momentarily dropped to 14._ V. Watched the reading as the a/c cycled off and on: steady 20._ V reading. Conclusion is this transformer powers the doorbell and not the HVAC. Jul 13, 2023 at 22:19
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It is the furnace transformer. Don’t mess with it. I just went through the same thing. I actually made the same exact post like a month ago for ring doorbell.

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  • Thanks! Did you end up finding your doorbell transformer? If so, where and how? Dec 29, 2018 at 6:41
  • No. I ended up having enough power at my doorbell so I lucked out and didn’t have to change it. But did you check behind your current chime? Sometimes they are behind it. You can also buy a tool that traces the wires in the wall for you.
    – C Fella
    Dec 29, 2018 at 11:16
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Look in the attic for the doorbell transformer, this is the most common place I have found them from early 1900 era homes and up to the 80's , close to the furnace is usually the furnace. Many times the location of the transformer is above the chime or a few feet from that in the attic. This is where I find them for the most part but seeing your furnace switch and transformer I would bet it is someplace close above the chime and may now be covered by insulation.

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  • Thanks! It so happens that the furnace is a few footsteps away from where the chime is, so that probably contributed to my confusion. Dec 29, 2018 at 5:01
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Our doorbell transformer is on the furnace. I think it is common in some homes.

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HVAC and water heater closet

In our HVAC / water heater closet there is a transformer on the drywall next to the furnace. I always thought this was the doorbell transformer and the HVAC transformer was inside the case of the natural gas furnace.

It is 102 F outside right now and I don't want to do anything to make the a/c go down. I don't have a current clamp and I am trying to figure a way to test without disconnecting anything

I clipped my Fluke 115 in V a/c mode to the exposed contacts of the transformer: reading 20.2 V. Had a family member ring the doorbell: reading momentarily dropped to 14._ V. Watched the reading as the a/c cycled off and on: steady 20._ V reading.

Conclusion: this transformer powers the doorbell and not the HVAC.

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