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NYT on Household Energy Monitors

Last week the New York Times Wirecutter ran an article whose headline posed a question; Do You Really Need a Home Energy Monitor? It’s an interesting question.

Wirecutter - Do your really need a home energy monitor

They say only that you might save some money. Maybe. And they even question that assertion. Well, we installed a Shelly 3EM last year for reasons that the Wirecutter article completely fails to mention. So, I thought it worth sharing our experience.


We live in Texas where there has been quite a bit of concern about the reliability of the public electric grid. Over the years, there have been many instances of regional outages arising from storms of all sorts.

2008: After Hurricane Ike

In 2008, after Hurricane Ike our neighborhood was 21 days without utility power. That was before we owned a generator. A neighbor tossed an extension cord over a fence. His 7 kW generator powered both households. We returned the favor by seeking out fuel, which was difficult to get for a time.

That one extension cord across the fence meant we had access to about 1,400 Watts. That was enough to run the fridge, fans, a couple lights, the network core, laptops and mobile phone chargers.

In 2017 we bought a used 8 kW portable generator from a neighbor. The purchase was inspired by the for-sale listing and the memory of Ike. We bought it without really thinking in detail about our requirements. As we have natural gas appliances, I guessed that 8 kW would run everything in our home except the central air conditioner.

2021: Winter Storm Uri

Last year, the Great Texas freeze of 2021 caused us to lose power for three days, even as temperatures dropped to 15F! As I described earlier, in that one week the generator really proved it’s worth. It also pointed to a problem running the furnace on the irregular power provided by a portable generator.

After the Great Texas power crisis of 2021, as the spring grew hotter, we were facing replacement of our 20-year-old central air conditioner. In going forward with that project we opted for a new, variable speed air conditioner. While more costly than a traditional AC unit, we thought the VS unit would be more energy efficient.

Further, since it did not draw a huge amount of power on start-up, it could be run on a largish portable generator. It would ensure that we had reliable heat and/or cooling in the event of another grid failure.

Toward the end of 2021 we upgraded to the newest 9.6 kW Predator Invertor. This is new model is more capable, dramatically quieter, and more fuel efficient. The clean power of the “invertor” is required to reliably power sensitive electronics, including the digitally controlled VS AC and furnace.

Shelly 3EM

To be able to manage the potential of running on generator power I needed to better understand our pattern of electric usage. So, I installed the Shelly 3EM on the mains input to our breaker panel. The Shelly device is a way to directly read our power draw in real-time. It can be read in the Shelly app on my phone.

I also have it integrated into our Home Assistant server. Starting in May 2021, Home Assistant includes a module specifically intended to track energy usage in support of homes with solar installations.


I was initially quite happy with the Shelly 3EM. It told me what I wanted to know. The house draws 300 – 500 watts at idle during the morning when we are at work. That’s the fridge, wine fridge, Tivo Roamio, network switch and some small electronics.

When the air conditioner runs hard it draws around 4,400 watts. We’ve never had the house draw more than 5.2 kWh thus far.

HA Energy Use July 13

This tells us a few things about running on generator power:

  • When it’s warm, we can run the air conditioner (4.5 kW)
  • In the winter, we can run the furnace (1.5 kW)
  • We can run all of our electronics; Tivo, TVs, network, computers, etc. (<1 kW)
  • We can use the coffee maker (1.4 kW)
  • We can do laundry
  • We can use the microwave oven
  • We can use the dishwasher

The most important thing we have learned is what we cannot do. We cannot run air conditioner, while doing laundry, making coffee and washing dishes. We simply can’t run everything all at once. We have to live within the 7,600 Watts the invertor can deliver continuously.

Beyond guessing, the Shelly 3EM has allowed us to know that the base load of the house with the air conditioner running is around 50% of what the invertor can deliver. That’s about ideal. Most especially if we need to run on generator power for an extended period.

An Installation Issue

Shelly is a European company. The 3EM is designed to be mounded on DIN rail, which is not common in US breaker panels. Even so, it’s small enough to be tucked into a corner of our new 200 Amp breaker panel.

However, being inside the all-metal breaker panel, which is itself on the exterior wall of the house, is bad for connectivity. This situation causes the little Shelly to occasionally drop off our Wi-Fi. Not often. Just every now and then.

When this occurs the Shelly retains its tracking data, to be uploaded when connectivity is restored. I admit, this is really a minor issue.

Seeking An Alternative

This little inconvenience lead me to acquire the Emporia Vue 2 which is one of the energy monitoring devices reviewed in the Wirecutter article. It has an external Wi-Fi antenna that’s designed to fit into one of the standard knockouts in the breaker panel. This should ensure continuous wireless connectivity to our network.


The version I bought can track the mains power and 16 separate circuits. That has the potential to provide more granular data about where power is being used in the house.

Alas, the Emporia Vue device is physically larger than the Shelly 3EM. Given the volume of wire existing in our breaker panel, it simply does not fit. So, I have yet to install it.

I am considering adding a small box connected to the breaker panel by rigid conduit to facilitate installing the Emporia Vue. Looking around online I find reports of other people having done something similar.

If I did that, I’d need to create extension cables for all the little current sensors. They use common sub-mini plugs, so that would not be too difficult. I just don’t know if it’s worth the trouble. I may just resell it.

Needful or Not?

That gets to the question of “need” posed by the Wirecutter article. To address our concerns about backup power, I need to know about our overall use of electricity. While on utility power we don’t gain much from monitoring every circuit.

My initial plan was to use two of the smaller circuit sensors to monitor the connection to the generator. When utility power was lost and the manual transfer switch cut over, we’d have real-time visibility of the load presented to the invertor. That could be useful.

To be fair, the Emporia Vue with 18 sensors costs the same as the Shelly 3EM. The lesser model that only reads the mains is under $100.

Instrumentation is Addictive

This fact is manifest in many ways, from Fitbits to Apple Watch and fancy home exercise equipment. People like to have data. Knowing is better than guessing. Hope is not a strategy.

The installation of the energy tracking hardware allows us to know more about how we use power. That insight lets us be confident we have a strategy for running on limited backup power in the event of a significant outage.

P.S. – Even as I was writing this, a later afternoon thunderstorm caused a brief power outage. Happily, it was just a few minutes and our UPSs kept the computers and network core running. No need to connect up the invertor. It sits quietly parked in the garage, awaiting its opportunity to shine.

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