Smart Thermostat Buying Guide: What Works With Your Heat
Before you pick Nest or ecobee, look behind your old thermostat. A gas furnace with a C wire works with every major smart thermostat. No C wire means a power adapter or a thermostat that ships with one (ecobee includes one). A heat pump needs a thermostat set up for the O/B wire and auxiliary heat. Old wall furnaces with two thin wires (millivolt), 240 volt baseboard heaters and mini splits do not work with Nest or ecobee at all; they need their own kind of controller. Install from $139.50.
Why listen to us: Zomg The Handyman crews have done more than 10,000 jobs across all of California since 2009, and every winter the calls change: lights on rooflines in November, cold rooms and dead water heaters in December and January, then leaks, clogged gutters and drafty doors once the storms arrive. This guide is what our installers tell customers before they buy, so the thing you order is the thing that fits your house. Most smart thermostat calls we get are not about which brand is best; they are about a thermostat that was bought, does not fit the wiring, and is now sitting in its box.
Quick Comparison
| Pick | Best For | Price Tier |
|---|---|---|
| Best for Most Furnaces | Google Nest Learning Thermostat (4th gen) | Premium tier |
| Best if You Have No C Wire | ecobee Smart Thermostat Premium or Enhanced | Premium tier |
| Best Value | Amazon Smart Thermostat | Value tier |
| Best for Mini Splits | Sensibo or Cielo Mini Split Controller | Mid tier |
| Best for Baseboard Heat | Mysa Smart Thermostat for Electric Baseboard (line voltage) | Mid tier |
Our Picks
Step One: Take a Photo of Your Wires
Turn off the furnace at the breaker or switch, pull the old thermostat off its base and photograph the wires and the letters they land on. That photo answers almost every question below.
| What you see | What you have | What works |
|---|---|---|
| R, W, G, Y and C | Furnace and AC with a common wire | Any major smart thermostat |
| R, W, G, Y, no C | Furnace and AC, no common wire | ecobee with its kit, or any brand plus a C-wire adapter |
| R and W only | Heat only furnace | Most smart thermostats with an adapter or a new wire |
| O/B, AUX or E terminals | Heat pump | Nest, ecobee, Honeywell set up for a heat pump |
| Two thick wires, 240 V label | Electric baseboard (line voltage) | Line voltage thermostats only (Mysa type) |
| Two thin wires to a wall furnace, no transformer | Millivolt wall or floor furnace | Millivolt-rated thermostats; most smart thermostats do not work |
| No wall thermostat, a remote | Mini split or window unit | An infrared controller (Sensibo, Cielo) or the maker's Wi-Fi kit |
The Three California Setups That Catch People
- Wall furnaces in older homes. Many California bungalows and apartments heat with a gas wall or floor furnace that powers its own thermostat with a tiny millivolt current. A Nest or ecobee has nothing to run on. Look for a thermostat sold as millivolt compatible, or keep the old dial; most of these furnaces have no clean smart option.
- Heat pumps. New homes, ADUs and many remodels now heat with a heat pump. The thermostat must know whether your reversing valve is energized in cooling (O) or heating (B), or the system blows cold air in winter. If you have backup electric strips (AUX), set a lockout temperature so the expensive strips do not run on mild mornings.
- Mini splits. A wall thermostat will not control them. Use the remote, the maker's Wi-Fi kit, or an infrared controller.
Settings That Save Money in a California Winter
Most California utilities bill homes on time-of-use rates with the highest prices in the late afternoon and evening (often 4 to 9 pm). For electric heat and heat pumps, a smart thermostat can warm the house a little before the peak window and coast through it. For gas furnaces the bigger win is simply a real schedule: lower overnight and while the house is empty. Ask your utility about smart thermostat rebates before you buy; several California utilities have offered them.
Before You Install
The jobs that go long are the ones that skip these.
- Turn the power off at the furnace switch or breaker, not just the thermostat.
- Photograph and label the wires before you disconnect anything.
- An old thermostat with a glass bulb contains mercury. In California it goes to household hazardous waste, not the trash.
- Measure the paint shadow of the old thermostat. A trim plate covers it; patching and painting is a separate job.
- Check your Wi-Fi signal at the wall where the thermostat goes.
Buy It, Then Let Zomg Install It
Our crews install what you buy, from Amazon, Costco, Home Depot or Lowe's, anywhere in California. What it costs on our booking page:
- Smart thermostat installation (Nest, ecobee and others): $139.50. With a C wire added: $171. A programmable non-smart thermostat: $112.50.
- Thermostat programming and app setup only: $117.
- Mini split heat pump installation (MRCOOL and Pioneer): from $1,345.50.
- Seasonal heater and AC check: $148.50.
Prices are from our booking page in November 2026 and are what you pay for the work; the booking page always shows the current price and every option before you confirm.
More: best smart thermostats 2026, smart vents and zoning, MRCOOL installation.
Need help with this in California?
Zomg The Handyman installs what you buy, across all of California. Upfront prices, 4.9 rated on Google, same-day slots available.
Book Smart Thermostat Installation →Frequently Asked Questions
Do I need a C wire for a smart thermostat?
Most smart thermostats need steady power, which is what the C wire provides. Without one, use a thermostat that ships with a power kit (ecobee) or add a C-wire adapter. Zomg adds one as part of the install for $171.
Will a Nest or ecobee work with my wall furnace?
Usually not. Most gas wall and floor furnaces use a millivolt thermostat with no transformer, and Nest and ecobee need 24 volt power. Look for a thermostat sold as millivolt compatible.
Can a smart thermostat control a mini split?
Not a wall thermostat. Mini splits use an infrared remote. An infrared controller like Sensibo or Cielo, or the maker's own Wi-Fi kit, gives you app control and schedules.
Why does my heat pump blow cold air after I installed a smart thermostat?
The O/B setting is probably wrong, so the system is cooling when you ask for heat. Change the reversing valve setting in the thermostat's equipment menu.
How much does Zomg charge to install a smart thermostat?
$139.50 on our booking page, or $171 when a C wire needs to be added.
Our service areas: Electrical Work in Los Angeles · Electrical Work in San Diego · Electrical Work in Irvine
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