Furnace on in the Summer?

Starting in June, Sense found my “furnace”. Obviously, living in the Northern Hemisphere, my furnace was not on. I though “well it must be the blower”. No. Dehumidifier? Nope. Both devices have been off numerous times the “furnace” has turned on.

What I know: it almost always is on for exactly 10 minutes. There’s a spike at the On for 800w and 450w the rest of the time. It has been on for less, 7 minutes, and longer, 13 minutes. 8am, 5am, 10am, 9am are all times it’s turned on this week. I have a KP115 on my ice-making fridge, and I don’t see these spikes in that power meter.

Most likely: my old basement fridge. It has no ice maker or fancy electronics. It could be the defroster, right? So it turned on and I ran to the basement. Watching the main Sense power meter, not the device power meter, I unplugged the fridge. 400w did not come off as I hoped. In fact, no power dropped because again, this fridge doesn’t have wifi or anything devised after April 2003.

I’m at a loss now. No clue what’s left. I can’t start flipping breakers in the middle of the day, so hopefully these screenshots and information can start getting the ball rolling.

In my books, it looks like a good-sized motor. Could be part of a compressor, large blower or pump. Does the waveform align with your furnace air handler coming on for fan or AC purposes ? My thermostat turns on the furnace blower for more than just heating.


I second what @kevin1 said. The spike you see is startup amps which motors pull. LED lights for example won’t have startup power.

Check the thermostat to see if you have it set to turn on the fan for X minutes per hour. As Kevin mentioned many of us, myself included, have the fan blower come on to circulate air even when the heat/cool is off. The time can vary because let’s say my AC ran for 5 minutes and I have the fan set to 15 minutes per hour, only 10 minutes is needed to complete the 15.

If it’s not the furnace think about other motors that you might have. Pumps can also have startup power.

I’ve had some discoveries that really were head scratchers. The best advice I can give is to look at these things:

  • Time that it turns on and off (see if there’s patterns) (see if it’s just at night etc)
  • Time that it stays on (see if there’s patterns)
  • See if there’s startup power (determines type of device)
  • About how much power is being used to size up the device

A good example of one that threw me off for a minute was my landscape lighting. No startup power, came on at night, decent amount of power and went off in the morning. The time that it came on and went off was what led me to figure it out.

I thought so too, but I’ve been working in the office when Sense says the “furnace” has turned on, and nothing has changed. When my fan kicks on, I hear a little thud and then hear the air moving. In these cases, nothing. I have occasionally turned on the blower manually to try and get that detected. Those screenshots are below, and look fairly similar, but again I’ve never heard it actually turn on. The next thing on my list is to kill the AC’s breaker when it’s on, but timing needs to be just right fore to be able to.

When Sense thinks of a “furnace” what does sense think it is? Resistive heat? Blower? Something else? All three combined? I have a gas furnace, so if Sense is looking for resistive heat, it’s completely misguided. Lastly, I have a Honeywell thermostat and it’s very basic. It doesn’t have any fancy “airwave” feature, and my fan is set to Auto, not On or Circulate. I agree that everything seems like it should be the blower, but right now none of the data is lining up.

Manually turned fan on

Manually turned fan off

Two manual on and off cycles

My basic Honeywell app fan settings

The correct Sense suggestion screen. No I don’t have a jacuzzi, sump pump, or a 480w light.

Sense doesn’t really see something as a “Furnace” it sees patterns in electrical signatures that it recognizes. That device is then selected from a list by users. Over time, Sense recommends ideas for what a similar electrical signature could be, based on what other people have selected it as. Depending on the type of furnace you have there’s a number of things that Sense can isolate out from the device. The fan (air handler, blower motor, etc), the compressor and the heat strips if those items exist. In your case, it would be the first in the above list, or a “motor,” as you stated that you have a gas furnace. The reason it doesn’t combine them is because they can all be used individually and all consume different amounts of power and have their own signatures. We tend to think of a furnace as one device, but in reality there’s often multiple power consuming devices within that box.

The signature is there, the power is being used. The issue isn’t really that Sense is misguided, it’s that you haven’t figured out what it is. The suggestion of a furnace is just a suggestion. When my blower motor was found (in a heat pump) and when my dryer was found they were both labeled as “Heat 2”. Both of those were incorrect.

Here’s my suggestion:

Set the “On” to notify you when it goes on. When it goes on take a look around the house to see what is on. While LED lights won’t pull startup power, a bank of CFL’s will, landscape lighting will, lights with transformers will. Your power signature looks just like my power signature for my landscape lighting. While it may not be lights, Sense is recommending that as the highest probability. Remember that 400w could be a bank of recessed lights in the Kitchen. It could be a garbage disposal, a trash compactor, garage door opener. Every house is different, but it’s not something really small or power from a standby device so you should notice when it’s on.


As a Sense user and forum lurker for 18 months now, I’ve done all these already. That’s how I was able to unplug the basement fridge when it turned on, because I’ve had the notifications on since it was first detected. We have no bank of recessed CFLs. The 12 100w can lights have all been replaced with LEDs that are on non-smart dimmer switches. My kitchen was renovated in 2019 with LEDs on non-smart dimmer switches. The only landscape lighting is battery-only powered. Disposal on a switch, no compactor, and garage door notifies me when it’s open. This is a 1919 house that has never been gut renovated. There’s not much this furnace could be, which is why it’s so puzzling to me.

I also think the exact 10 minute “On” duration most of the time hasn’t been considered, especially when it turns on automatically overnight.

The best of us overlook things. I’m not suggesting that it be any of the things that I listed out, I’m only offering up ideas.

I considered it in a previous post about the air handler and it also appears that it’s not always 10 minutes. Even in the screenshot you just posted it shows it was only for 3 minutes.

Here’s the problem… No one but you knows what you have in your house. I’m only reinforcing some basic techniques that I’ve used to discover what devices were. Here’s some examples from my house that look similar.

Air Handler:

Landscape Lighting:

Air Conditioner:

I wish you the best of luck and if anyone else has any ideas I’m sure Brian would be more than happy to entertain them.

Do you have a coffee maker that keeps a tank of water warm ready for brewing?

Good question. We had a Keurig, but don’t use it anymore. We have a normal coffee maker again. I hooked a kil-a-watt meter to it for a while, and in standby, it doesn’t use any real amount of power.