The Half Wattage issue


There are many post on this topic of the graph, power meter and device pages
reporting half the wattage on 240 appliances. I spoke with tech support about
this in length and they know of the problem and really don’t seem to have a
good answer other than its reading one leg and not the other. I was told to give
it time to keep learning.
I thought the same thing about one leg being read when I first encountered this
but I now do not think that is the case. Well, it could be but they had no idea
why I have a 120 volt device that just uses one leg, reporting the same half
power wattage usage.
I’m pretty sure I know what the deice is that I’m seeing. It’s electric 120 volt
under tile floor heat. When on it draws 540 watts as confirmed with kill-a-watt.
Sense is showing it at approximately half where it ranges from 230-270.

Out of curiosity. Has anyone else seen the same with any other 120 devices?
If so. has it been reported?


It would be very odd for the power meter to report an incorrect value. That is a real time measurement with no machine learning algorithms applied. See if you can watch the kill-a-watt display in real time and correlate it with the power meter bumps. I have a feeling it’s a different device.


that’s exactly what I had done. cut the 12/2 wire in the crawlspace
coming straight from the breaker and feeding only the floor and
put a plug on it. I then placed the plug into the kill-a-watt and watched
in “real time” where the kill-a-watt displayed right about 540 while sense
displayed 243 or something like that.
Here is the issue with the graph, it is not as real time as what you are thinking.
The raw readings the sense is taking are not fed directly to your phone or app.
Those readings go to the cloud and are then sent to our phones. We don’t see
the raw data.
In the beginning, I thought we would see raw data but without internet you get
nothing whatsoever. I’ve actually asked them if this could be done. Not for any
other reason than just to view the graph in real time.
I have tried this same test with a known 1500 watt heater and it has shown correctly
everytime i’ve tried it. Just tried again and read 1514.
The floor is wired back up now and I can turn the thermostat on and off with only
a few times the500 watt load under other as its not yet detected.
its the only 120 i’ve had this happen with. all my 240 show half but it
will probably rectify itself in time
I said something wrong, sorry. Not all 240 are half off my emergency heat strips
show the full 15.000 when they come on under other.
Maybe someday we will have a way to view 240 and 120 usage separately


As I mentioned before, you can’t entirely rely on those “wattage detail” flags.


I’m presuming you’re referencing the bumps in your image above?

How do you know for sure that that on and off load is what you think it is (your under floor heat) and not something else in your house? I can think of a lot of things that present as little on/off bumps like that. Have you disconnected the under floor heat and confirmed those bumps stop?

And if it’s a 120V system running your in floor heating, I’m not sure what you’re talking about with regards to it only drawing from one leg and not both - only 240V devices draw from both legs at once. 120V devices draw from one or the other, not both.

My thought is that your under floor heat is part of the other ~4300W your house is drawing at that moment in time and those bumps are something completely different.


It’s not just the flags. I cant rely on any of yet.


I’ve found that you can look at the delta by comparing the readings from the “needle” in two different places and they will subtract out to a different value than the flags. But when I compare my realtime house power meter (via a Eagle) it is exactly spot on with my Sense Power Meter. I think you are wrong to distract the Sense readings all lone as your house has been properly calibrated and your clamps haven’t come loose or resituated them selves since calibration.

From my meter - Here’s exactly how my electric company sees it…

From my Sense - the main issue is that my revenue meter samples much more slowly than the Sense, so the Sense is in reality more accurate on time resolution, even with the data going back to the mothership first.

BTW - please notice that I placed the Sense “needle” at roughly the point that the Rainforest Eagle crossed the 1650W line. Sense says 1665W.


That’s what i’m saying, 120 is only one leg, never both.
How do I knw? Try turning something on and off 50 times in
a few minutes while the timeline updates, coincidence is
out of the question. Not only that, I’ve been studying this on the
kill-a-watt and the timeline for about 7 days now.
This floor heat was is UL listed for right at 4.5 amps.
following OHMs law and basic electricity there is no explanation
for this discrepancy, also confirmed by tech support.
I can see all but one of my 240 are half off but this is the only 120.
Right now my 3 ton heat pump is showing 2700 watts. That impossible,
the math doesn’t add up. That half of what the compressor and outdoor fan
consume running together. And on all appliances and devices the missing watts
o not show up in other.
You can see that in the screenshot. If the other half of the heat pump was in
other than other would be at least 2700, its not and what about everthing else
that hasn’t been detected? That would be in other on top of that 2700.

I’m open to suggestions as I would like to get this figured out but the screenshots
and test don’t lie.


So by your logic…are you suggesting that in your first screenshot…your house was actually consuming nearly 10,000W at that moment in time?

As for assuming your heatpump readout is correct, as others have mentioned before, you are only in the very beginning stages of detection. Although you have got an amazing amount of devices detected already for having been a user for only a short period of time, you cannot at this point assume all are 100% correct or complete. Your heat pump readout for example could be only a portion of the unit - a compressor, but not associated motors or heating elements and such, for example. Just because Sense detected something and may have named it something HVAC related doesn’t mean that it detected every component of said hardware.

There’s still 1600+ watts of “other” showing…and was your oven actually on when you took your last screenshot?


Not at all. It was consuming more than it was showing. Did you see where I corrected about my 15,000
watt heat strip always show correctly? I’m saying 15kw was correct but the additional was affected by
120 and 240 devices with the 120 being correct and 240 only half.
I’m aware of being extremely early in and it taking time. I am not bothered by that at all its just curious
to me why I would have one oddball 120 device. The 240 will catch up at some point in time and this single
120 heater show correctly sporadically. I just wondered if it was common with others to have something
120 doing this half thing. I’ve assumed from the beginning is was picking up 120 or one side but just
made no sense to me why 120 would do it. I was hoping for some education from everyone with more
experience and knowledge, that’s all.
I saw that too about the oven so the other should have been showing the other leg of the heat pump, air handler and oven. I also know for a fact hat my oven element is a 3500 watt element. So there should be the other 1700 in other from just that and the left over 240 not showing frm the heat pump and HVAC system which would be at least 2300 based on known wattage, amperage and voltage. See what I mean?
Other should have the total of the other half of the 240’s in the screenshot. I chalk this up to needing the
required time for learning.
Does that sound right to you? and, did I explain that well enough in how I understand and interpret
what I’m seeing?


Hi Dan,

I think there may be a couple things going on as in reading your notes, I know I have managed to confuse myself between your comments of 120V vs 240v devices, and “one side” of a 120v leg and then the half reported wattage of your 540watt radiant floor etc…

What many of us have seen an experienced especially in early days are 240v devices only having one leg of the 240 picked up. So a 3500 watt hot water heater appearing as a detected device of “hot water heater” showing 1750w, and then the other half appearing in Other.

I think that is what we are all assuming you are talking about, but now looking at that screen shot a bit closer, I see where this might be something totally different and i’m wondering if there is a red herring in all of this making it more confusing.

Your heat pump. I get what you are saying about the numbers not adding up if heat pump were only half, but I would then say - are you sure that the device called Heat Pump is what you think it is? Is it possible that some part of your heat pump at either 2700w or 5400 watts? I’m not sure if you named that Heat Pump or if Sense did, but even if Sense names something, take it with a grain of salt. Most likely unless its a simple device with only one component (a space heater, pump, vacuum etc…) Sense probably only identified a part of it. Is it possible that Heat Pump isn’t the device you think it is?

Similar question for your Oven. Is it a 3500w heating element? or is the tag on the oven for 3500 watts combined between heating elements? Only able to draw from personal experience, but my oven has vastly different energy draws depending on cook temperature, if its pre-heating vs broiling etc…

While I realize that the “Now” tab isn’t direct from the device and is routed through the cloud, I don’t think anyone here has ever seen the bottom right corner number be wrong. You mentioned that when you plugged your 1500w heater in, you did see the that number adjust the amount you would expect. So let s assume that that number is correct.

Regarding the floor heater - If you turn it off for 30 minutes, do the ~215w pulses stop on the power meter? And then if you turn it back on, do they start up again?

When you were under the floor and saw it pulsing to the 540watts you expected, were you turning it on and off, or is that its “regular” pattern when its heating? Or had you just turned it on, so it was working harder to get to temp? I don’t know a lot about electric radiant, but I’m just thinking about my induction cooktop. Depending on heat setting, it both varies in frequency between pulses, and amplitude of the power draw. Is it possible that your floor regulates these things based on a temperature probe? Ignoring the 200w labels on the power meter, if you turn the floor off, does the instantaneous power meter in the bottom right corner drop by about 550w?

Last question because this certainly is odd. I would assume that support would have checked this, but can you a look on your phone in the Sense app - Settings/My Home /Sense Monitor and see if the information under Signals looks correct? If you haven’t discovered this page before, it can be helpful for troubleshooting and device detection because it shows you power and voltage per leg. Which leg you ask. I’ll save that for another conversation, but just know that yes, people have asked for these to be labeled and presented in the info panes of detected devices.

This turned into a much longer post than I intended. I’m trying to break down the issue a bit and see if they are connected or not because it does feel that either you have some compounding issues, or you are having an experience that no one else seems to have had.


Ok, First off, thank you so much for the response. I think we are mostly on the same
page as with the others that responded.
When I speak of legs, I mean one side of 240. So 240 has 2 legs but 120 has a single leg.
The strange floor heater has only a single leg. Its one side in total of say a dryer or heat pump with 2.

I’m absolutely sure sense naming of the heat pump is correct and I’ll you why. I have notifications turned
on so I get the alerts when it turns on and off. The outdoor unit of the heat pump is directly outside the
windows 3 feet to my left so each on or off alert, corresponds to what I hear. I do understand what you explain with what sense is picking up. When my heat pump turns on it has a minimum of 3 devices. Outside its the compressor and condenser fan (approx. 4500 watts) and the air handler fan(300-500 watts) and possibly some of the heat strips (5,000, 10,000 or 15,000: installer states only runs at 15,000).
So if it shows my heat pump running at 2700, it has to be half. compressor and condenser fan 4500 and
if air handler included an additional 3-500.
I totally agree and feel is still playing catch up with all 240 exceot the 15,000 heat strips.
You make a VERY GOOD point in that I have not turned the floor heater off for an extended time.
That’s exactly what I will do tomorrow (after the wifes bath or shower) and the type of help I am needing
as the possibility that I’m looking over something is always there.
I have the same variations for things like cooktop or oven reaching a heat or trying to maintain a steady
state after the initial heat up but have not seen a pattern with the floor. I haven’t allowed the floor to cool
much and turning it off for longer may shed some light.
I love the signals page from your last question. Having OCD it makes me desire everything to be “balanced”
in which it is close. That particular page seems to be the most accurate for real time usage at the stage
my sense is at. The total from each leg added together appear to be what I feel they should be if the other
locations were gathering from both legs.
Thank You, I’ve got something to check that I had not thought about.


I think You are correct with the red herring theory. I haven done much but I
did allow the floor to cool to 79 degrees (set at 92).
When I cycle it from the cooler condition, it shows as 540-550.
Something in the thermostat?
Its a simple concept as its about 400 feet of heat tape. It would draw
the same unless the thermostat is cutting it back.

Water heaters second leg is now picked up,


Just a hunch. Is it a PWM controller? I think (someone please correct me) that that would make the wattage look funny.


I don’t think so but not sure.
I did find in the thermostat options for installation that you an set
the output power going to the tape to whatever percentage you
would like. So a setting of “50” would be half the 540. It was set
as default at “0” which is 100%. But I don’t know if that setting is
the maximum it will use or the only power state it uses. I’m thinking
it must be the maximum and it determines what it needs to do by
current floor temperature.
This thing comes on every single minute of the day. Only for a few
seconds unless its cooled down. The sense went back to showing
what I thought was half after the floor got up to 92-95 and it was just
trying to maintain.
So, I was WRONG and SENSE is right.


@samwooly1, Just wanted to say: I’ve had my Sense monitor for well over a year. And I just wanted to chime in real quick to say that I’ve observed exactly the behavior you mention repeatedly (and on different devices, and via different app versions)…
The timeline graph “total” always appears to be accurate. However, the underlying Sense data is always a stream of 2 different mains… in my experience, the little tags (which are well documented as a bit unreliable [probably at least partly for this reason, huh!?!]) seem to only track one main at a time (so: for many 240 devices, the tag will show only “half” the wattage). However, once a device is detected, then the tags are “better”.

One way to think of this is to just figure that no matter how “vertical” the spike may look, there’s likely a tiny difference in the waveform of the 2 mains, at least… so when Sense is reporting those increases/decreases: just assume that they are being ridiculously strict differentiating between the 2 mains (even though you maybe can’t see the distinction at the lower resolution that the timeline shows)… this is really complex data (as you know), and the timeline shows a beautifully informative, but simplified view of the underlying data.

Hope that helps! I’ve seen the exact same thing as you have (and I have several devices that exhibit this behavior with a ton of really clear examples).

PS: as a side note: Sense is just frankly a bit “weaker” at 240 devices almost universally… I think it has to do with the underlying AI tech they use (but I know this has been improving rapidly recently). Conceptually, it would be easy to see an increase/decrease of “equal” usage on both mains at the same time and conclude: probably 1 device. But, Sense just isn’t great at that quite yet (in my experience).


If your a year into it and still experiencing this then it sounds like
I need to prepare myself to be in for the long haul. I agree that
conceptually it’s seems like it would be a no brainer to connect
the two legs when a device is identified and pulling close to the
same from the second leg. I have noticed that others have commented
about it from the beginning so I assume its not the easy fix I imagine
it to be.
I can definitely see improvements with my monitor on an almost daily
basis. I think I stated earlier today that there were three new detection
at the same time today, it was actually FOUR.
I only recognized it as three because Sense had combined the fourth
with my oven. I think it could have made a mistake but I cannot test it
because it’s not “merged”. When they got “combined” the new one disappeared
completely. I don’t care for this feature. I think it should allow us to review and
accept or decline the combination. Sense may feel correct about it but we could
help to confirm it.
I haven’t researched anything about “combine” yet but I like merging a lot better.
Since the combination there have been false alert for my oven being on when
it was not but the dryer was. The dryer I already had detected has not shown on
or popping up on the timeline since they combined.
I’m hoping they can and will roll this back.

I wanted to add that I would like to have something like a “group” function where
am appliance or device could be merged and see all components as one or grouped where
the individual components could be seen. My fridge has 12 components alone.


That Sense can offer you! Well kinda. They don’t offer a grouping that lets you see the individual items and the hole. But you can merge devices. I know there are still parts of my fridge that haven’t been detected yet, but the water dispenser, ice maker and general compressor were all detected as individual devices. I merged them so I only have a single “Fridge” device in my devices list. You do this via the settings “gear” on a device.


Thank You.
I have merged one device so far and that works well.
I don’t care for sense “combining” devices because it
disappears once combined. Apparently combining and
merging, while sounding the same, are not.
Sense I think got this combine wrong as my oven and
dryer are getting mixed up ever since. Now my dryer isn’t
showing up when it is running but is still a device in the list
but the oven shows on when it’s really the dryer. It went
a little haywire.


It would indeed be very, very weird for those live readings to be incorrect, barring an installation issue like an open CT or Sense being mistakenly installed on a subpanel. I can’t think of any time I’ve ever seen that.

I wouldn’t necessarily assume this. Detection can vary dramatically across homes for various reasons. You’re off to a pretty good start already.

Check out this thread: Device Detection Update: Device Updates!
The only devices that should be getting renamed/autocombined are ones you have not renamed or marked as a “guess.”