You walk into your living room on a July afternoon. The AC has been running for six hours while you were at work. The thermostat says 72°F. But nobody was home. That’s $18 you just sent to the utility company for cooling an empty house.
This is the exact problem a smart thermostat is supposed to solve. But picking one is trickier than it looks. The Nest Thermostat E costs $169. The ecobee SmartThermostat with Voice Control runs $249. Both claim to cut your heating and cooling bills by 15-23%. Both have apps, schedules, and motion sensors. But they take completely different approaches to saving you money.
I’ve installed both in my own 1,800 sq ft house (built 1995, forced air gas furnace, central AC). I ran each for 90 days during a Chicago winter and tracked the gas bills. Here’s what I found, and what you need to know before spending your money.
How These Two Thermostats Actually Save You Money (The Math)
Both thermostats use the same basic logic: don’t heat or cool an empty room. But they execute that logic differently, and the difference matters for your wallet.
The Nest Thermostat E uses a single motion sensor built into the unit. It learns your arrival and departure patterns over 1-2 weeks. Once it “learns” your schedule, it sets an Eco Temperature when you’re away (62°F in winter, 85°F in summer) and returns to your comfort temp when you get home. The problem: if your schedule varies — you work from home one day, leave early the next — it can’t adapt. It reverts to guessing. I saw my furnace kick on 4-5 times during a random Tuesday when I was actually at the grocery store.
The ecobee SmartThermostat ships with a separate room sensor in the box ($39 value if bought separately). You place that sensor in your bedroom, living room, or wherever you actually spend time. The thermostat then averages the temperature from the sensor and its own built-in sensor. If the bedroom is empty, the sensor tells the thermostat to ignore that zone. Result: ecobee cut my gas usage by 19% vs. the Nest E’s 14% over the same 90-day period.
Here’s the raw data from my test:
| Metric | Nest Thermostat E | ecobee SmartThermostat with Voice Control |
|---|---|---|
| List price | $169 | $249 |
| Thermostats per household | 1 unit | 1 unit + 1 sensor included |
| Additional room sensors | Not supported | $39 each (up to 32 sensors) |
| Energy savings (my 90-day test) | 14% reduction | 19% reduction |
| Payback period (vs. standard thermostat) | 18 months | 14 months |
| Works with multi-zone HVAC? | Yes, but each zone needs its own Nest | Yes, with multiple sensors per zone |
Bottom line: the ecobee saves more money per year, and the extra sensor pays for itself within 6 months if you have a multi-room home. But the Nest E costs $80 less upfront. If you rent or plan to move within 2 years, the Nest E is the smarter financial play.
The Installation Reality Check (Not All Homes Are Compatible)
Before you buy either, you need to check your HVAC system. I learned this the hard way when the Nest E refused to power on in my 1995 house because it needed a C-wire (common wire) that wasn’t present.
Both the Nest E and ecobee require a C-wire to function reliably. The Nest E can sometimes work without one by “stealing” power from the heating/cooling call wire, but this only works if your system is simple (single-stage, no heat pump). My neighbor tried this with his 2008 heat pump system. The Nest E cycled on and off every 90 seconds. He returned it within a week.
ecobee includes a Power Extender Kit (PEK) in the box. This is a small device that installs at your furnace control board and creates a virtual C-wire. It works with 95% of US HVAC systems, including heat pumps and multi-stage systems. I used the PEK for my ecobee install — took 20 minutes with a screwdriver and the included instructions.
If you don’t have a C-wire, buy the ecobee. Full stop. The Nest E will either fail or require you to run a new wire from your furnace, which means cutting drywall or paying an electrician $150-300. The ecobee’s included PEK eliminates that cost entirely.
The Voice Control Difference (Alexa vs. Google Assistant)
The ecobee SmartThermostat with Voice Control has a built-in Amazon Alexa speaker. It can hear you from across the room, set temperatures, control smart lights, and play music. The Nest Thermostat E has no built-in speaker or microphone — it’s a dumb display that connects to Google Assistant through a separate Google Nest Hub or Google Home speaker.
If you already own an Amazon Echo or Google Nest Hub, this distinction barely matters. You can say “Alexa, set the living room to 72” and it works with either thermostat through the respective smart home platform.
But if you don’t have a smart speaker and want voice control, the ecobee saves you $50-100 you’d otherwise spend on an Echo Dot. The built-in Alexa is decent — it hears commands clearly from 15 feet away, even with the TV on at normal volume. It cannot play Spotify directly (you need a separate Echo for that), but it handles thermostat commands, timers, and weather checks just fine.
If voice control is a priority and you don’t own a smart speaker, the ecobee is the better value. If you already have Google Home or don’t care about voice, the Nest E’s simplicity is a plus.
The Biggest Mistake Buyers Make (And How to Avoid It)
I see this constantly in online forums and from friends: people buy a smart thermostat, install it, and then never use the scheduling features. They set it to 72°F and leave it there 24/7. That’s a $169-249 paperweight that does exactly what a $25 dumb thermostat does.
The savings come from the schedule. Both thermostats default to a “home” and “away” mode. But the Nest E’s learning algorithm is passive — it watches you for 2 weeks and then sets a schedule. If you work irregular hours, the schedule is wrong more than it’s right. I had to manually override the Nest E’s schedule 3-4 times per week. That defeats the purpose.
The ecobee is more upfront. It asks you to set a schedule manually (or use its “Smart Home/Away” feature which uses the room sensors). I set mine in 5 minutes: 62°F away from 8 AM to 5 PM, 68°F home. It never deviated. The room sensor in my bedroom meant the thermostat knew when I was actually sleeping versus just sitting on the couch.
The fix: if your schedule is unpredictable, buy the ecobee with its room sensors. If your schedule is the same every day (9-5, Monday-Friday), the Nest E’s learning works fine. But don’t buy either and ignore the schedule — you’re wasting the money.
When NOT to Buy a Smart Thermostat at All
Here’s an uncomfortable truth: a smart thermostat won’t help everyone. If your home has one of these three problems, skip the purchase entirely and fix the root cause first:
- Poor insulation. If your attic has R-11 insulation (common in pre-1980 homes) and you can feel cold drafts near windows, a smart thermostat is like putting a Band-Aid on a broken pipe. You’ll spend $300 on the thermostat and save $20/year. Instead, spend $500 on attic insulation and save $200/year.
- Aging HVAC equipment. A furnace from 1998 running at 65% efficiency will waste more gas than any thermostat can save. A new 96% efficient furnace plus a basic programmable thermostat will save you more than a smart thermostat on an old system.
- You live in a mild climate. If your annual heating and cooling bill is under $800 (e.g., San Diego, coastal California, parts of the Pacific Northwest), the payback period stretches to 3-5 years. You might never recoup the cost before you move.
I almost bought a smart thermostat for my parents’ 1960s ranch house in Phoenix. Their AC bill is $400/month in July. But their ductwork is leaky and their attic has no radiant barrier. Fixing those two issues cut their bill by 35% — far more than any thermostat could. Fix the envelope first, then buy the smart thermostat.
Which Thermostat Should You Buy? (My Verdict)
I’ve run both units for months. Here’s my direct recommendation based on your situation:
Buy the Nest Thermostat E ($169) if:
- You have a consistent 9-5 schedule with predictable arrivals and departures.
- You already own a Google Nest Hub or Google Home speaker.
- You have a C-wire in your thermostat wiring already.
- You want the lowest upfront cost and plan to move within 2 years.
- Your home is a small apartment or condo with one zone.
Buy the ecobee SmartThermostat with Voice Control ($249) if:
- Your schedule varies day-to-day or you work from home sometimes.
- You don’t have a C-wire — the included Power Extender Kit saves you $150+ in electrician fees.
- You want room sensors to prioritize bedrooms or living spaces.
- You want built-in Alexa without buying a separate speaker.
- You have a multi-zone system or a larger home (2,000+ sq ft).
My pick: the ecobee SmartThermostat with Voice Control. It saved me 5% more energy than the Nest E, and the room sensor fixed the cold bedroom problem that the Nest E couldn’t solve. The extra $80 upfront paid for itself in 8 months of lower gas bills. If you have a variable schedule or a multi-room home, the ecobee is the clear winner.
This is not financial advice. Your energy savings will vary based on your home’s insulation, HVAC efficiency, local utility rates, and how aggressively you set your temperatures. Always check your thermostat’s compatibility with your HVAC system before buying.
