Running a Home Energy Audit with Smart Devices

Last year I decided to figure out where my electricity was actually going. My power bill averaged about $180/month and I had no real idea what was eating the most energy. I knew the HVAC was the big one, but beyond that? Total guesswork. So I spent about two months doing a thorough home energy audit using smart home devices, and what I found surprised me. Some of the worst offenders were things I never would have suspected.

Here's exactly how I did it, what I found, and how you can do the same thing.

Step 1: Establish a Baseline with Whole-Home Monitoring

Before measuring individual devices, you need to know your total consumption. A whole-home energy monitor clamps onto the mains in your electrical panel and tracks total usage in real-time.

I used the Emporia Vue 2 (~$90 for the whole-home version, ~$200 for the version with 16 circuit-level clamps). The Vue 2 clamps around the main feeds in your breaker panel and reports real-time power consumption via WiFi to the Emporia app. The 16-circuit version also lets you monitor individual breakers, which is incredibly useful — you can see exactly how much each circuit is pulling without plugging in individual monitors.

The other popular option is the Sense Energy Monitor (~$300). Sense takes a different approach — it clamps onto your mains and uses machine learning to identify individual devices by their electrical signatures. After a few weeks of learning, it can tell you "your fridge used 45 kWh this month" without any additional hardware. The ML detection isn't perfect (it misses some devices and occasionally misidentifies others), but when it works, it's like magic. Sense also integrates with Home Assistant through a community integration.

I went with the Emporia Vue with 16 circuit clamps because I wanted certainty about which circuits were drawing power rather than relying on ML detection. Installation took about 30 minutes — you're working in your breaker panel, so if you're not comfortable with that, hire an electrician. It's a straightforward install for anyone with basic electrical knowledge.

After a week of data collection, I had a clear picture: my HVAC was about 45% of total usage (expected), but there was a surprisingly large baseline draw of about 400-500 watts even when the house was "idle" — no AC running, everyone asleep, everything supposedly off. That idle draw was costing me about $35-40/month. Finding where that was going became the mission.

Step 2: Hunt Down Individual Devices

To measure individual devices and outlets, I used a mix of smart plugs with energy monitoring:

• TP-Link Kasa KP115 (~$16) — WiFi smart plug with energy monitoring. Reports real-time watts, daily/monthly kWh, and runtime. Works with TP-Link's app and integrates well with Home Assistant. I bought six of these for the audit.
• Shelly Plug S (~$22) — WiFi smart plug with energy monitoring, supports local API and MQTT. Smaller form factor than the KP115. Also reports real-time watts and cumulative kWh.

I rotated these plugs around the house, leaving each device monitored for at least 48 hours to capture a full cycle (including standby periods). Here's where the surprises were:

The chest freezer in the garage: This 15-year-old Frigidaire chest freezer was pulling an average of 2.1 kWh per day, which works out to about 63 kWh per month — roughly $15/month at my electricity rate of $0.24/kWh. A new Energy Star chest freezer of the same size uses about 0.7 kWh per day. I replaced it within the month and the $400 new freezer will pay for itself in about two years.

The cable box: Our Xfinity X1 DVR cable box draws about 30 watts even when "off." It never truly powers down because it's recording shows and updating the guide. That's about 22 kWh/month or $5.30/month just to sit there. I can't put it on a smart plug because it takes 5+ minutes to reboot, which would be annoying. This is just a cost of having cable TV, and honestly it was one of the reasons we eventually cut the cord.

The gaming PC: My son's gaming PC in sleep mode pulls 8-12 watts. Not terrible. But he leaves it running (not sleeping) about 50% of the time when he's not using it, and at idle it pulls about 90 watts. I set up a smart plug automation to put it to sleep after 30 minutes of idle time, which saves about 25 kWh/month.

Phone and laptop chargers: This one was less dramatic than I expected. Modern chargers draw almost nothing when no device is connected — usually under 0.5 watts. The "unplug your chargers" advice was meaningful 15 years ago with old transformer-based chargers, but modern switching power supplies are very efficient at idle. I measured eight different chargers and none drew more than 0.3 watts when idle. Not worth worrying about.

Step 3: Check HVAC Efficiency with Smart Thermostat Data

If you have a smart thermostat (Ecobee, Nest, or similar), you have a goldmine of data about your HVAC efficiency. Look at the runtime reports — how many hours per day is your system running?

My Ecobee showed that during peak summer, my AC was running 12-14 hours per day. That seemed high for a 2,000 sq ft house. I put temperature sensors in every room (Aqara Zigbee temperature sensors, about $12 each) and discovered a 6-degree temperature difference between rooms. The upstairs office was hitting 80°F while the living room was at 74°F. The thermostat — located in the hallway — was reading 76°F and thinking everything was fine.

The fix was a combination of things: closing some first-floor vents partially, opening upstairs vents fully, and adding a ceiling fan in the office. The room temperature variance dropped to about 2-3 degrees, and total AC runtime dropped by about 90 minutes per day. That's roughly 4-5 kWh per day in savings during summer.

Step 4: Find Drafts with Door/Window Sensors

This is a clever trick I picked up from a home energy forum. Place temperature sensors near your windows and exterior doors, and compare them to sensors in the center of the room. During winter, if the sensor near a window reads significantly colder than the room center, you've got a draft or poor insulation.

I found that two windows in our dining room were reading 8-10 degrees colder than the room center during a cold snap. I could feel the draft when I held my hand near the window frame. Adding weatherstripping tape ($8 from Home Depot) and using window insulation film on those two windows noticeably reduced the draft, and the temperature sensors confirmed it — the difference dropped to about 3 degrees.

Aqara door/window sensors also report temperature, so if you already have them for security automation, check the temperature readings during extreme weather. They'll tell you which windows and doors are leaking the most.

Step 5: Track Everything in Home Assistant

Home Assistant's Energy Dashboard is genuinely excellent for this kind of audit. It pulls in data from your whole-home monitor, individual smart plugs, and solar panels (if you have them) and gives you a clear breakdown of where energy is going.

To set it up: go to Settings → Dashboards → Energy. Add your Emporia Vue or Sense as the grid consumption source. Then add individual devices (smart plug energy sensors) as device consumption. Home Assistant will generate daily, weekly, and monthly charts showing exactly where your electricity went.

The killer feature is the ability to compare time periods. I can pull up January 2024 vs January 2025 and see exactly how my changes affected consumption. After all the audit-driven changes (new freezer, PC sleep automation, HVAC balancing, weatherstripping), my average monthly bill dropped from $180 to about $145. That's a $420/year savings.

Step 6: Seasonal Comparisons and Ongoing Monitoring

An energy audit isn't a one-time thing. I keep the Emporia Vue permanently installed and check the Home Assistant Energy Dashboard weekly. Seasonal changes reveal different patterns:

• Summer: HVAC dominates. Focus on fan usage, thermostat optimization, and reducing heat gain (close blinds on south-facing windows during peak sun).
• Winter: HVAC still dominates but heating is more about gas in my case. Electric usage shifts to lighting (shorter days = more lights on) and holiday decorations (smart plugs with timers help here).
• Spring/Fall: Lowest bills. This is your baseline for non-HVAC usage and the best time to spot anomalies.

What I'd Recommend for Your Audit

Start with the minimum viable setup:

• One Emporia Vue 2 whole-home monitor (~$90) — this shows your total consumption and gives you the big picture
• Three or four TP-Link KP115 smart plugs (~$16 each) — rotate these around the house to measure individual devices over 48-hour periods
• A few Aqara temperature sensors (~$12 each) — place near windows and in different rooms to find hot/cold spots

Total investment: about $150-170. My audit-driven changes save roughly $35/month, so the monitoring gear paid for itself in about five months. And the monitoring keeps running — if something starts drawing unusual power, I'll catch it in the Home Assistant dashboard before it shows up as a surprise on the electricity bill.

The most important thing I learned: don't guess where your energy goes. Measure it. I was completely wrong about several things (chargers are not a big deal, my old freezer was a way bigger deal than I thought), and I would have wasted time and money on the wrong fixes without actual data.