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Millivolt thermostats play a critical role in safeguarding your home from unforeseen temperature fluctuations. They are instrumental in assuring that your gas heaters deliver the required warmth for your abode.

9.5 Honeywell Home
TOP PICKAn intuitive thermostat that is compatible with 750 millivolt and gas fireplaces
9.2 Lux Products
A millivolt thermostat with optional child-lock

Despite smart thermostats being the popular choice these days, only the Lux Geo-WH thermostat qualifies as a “smart thermostat”. Unfortunately, a number of users are having reliability issues with the app and software which is why we can't rank it higher.

What is a Millivolt Heating System?

A millivolt heating system is commonly found in floor heaters and wall heaters that have no external electrical power source. Such heaters include gas-fueled wall heaters or gas fireplaces.

This millivolt heating system can only be regulated by a millivolt thermostat. The thermostats used for a millivolt heating system might be programmable, non-programmable, Wi-Fi enabled or smart.

An intuitive thermostat that is compatible with 750 millivolt and gas fireplaces

While not officially a “smart thermostat”, the T5 has a number of smart features such as learning the heating cycle time of a fireplace or furnace to deliver the correct temperature.

Top Features
  • Temperature limits help save equipment and reduce energy bills.
  • Can be battery powered or hardwired
  • Nice back-lit interface

Honeywell T5 Touchscreen has a large backlit display and its touchscreen interface gives it quite a modern look.

The T5 thermostat can be powered either with an alkaline battery or C-wire. It features “Smart Response Learning technology” which learns how long the equipment takes to get the room to temperature and then takes that into account when executing the schedule.

What I liked
  • The device allows users to program each day of the week differently or with the same schedule for the whole week.
  • The thermostat is easy to set up and operate.
  • Honeywell is a well established brand in the heating controls industry
What I didn't like
  • The lack of geofencing features is a drawback for this device, as the feature is useful when trying to reduce energy costs.

The Orbit 83521 millivolt thermostat was designed to give homeowners the final say when it comes to the temperature of their homes.

Top Features
  • Nice, contemporary design should fit in every home.
  • Programming made easy with the ‘copy feature’, which allows users to copy and paste schedule times.
  • Saves 33% of energy costs with the energy star feature.

Decide and program the temperature of your home for 7 days (each day can have up to four different periods). 

The 9.3 ounces millivolt thermostat does not lose programmed data when the battery is replaced. Although users will have to reset the time and date, the personalized data remains intact and functional, which is very convenient and saves a lot of set-up time.

To save battery, the warm backlight turns off 10 seconds after the last button is pressed. Also, the device is designed with the ‘energy star feature’ which saves energy and money.

Tech Specs

The Orbit 83521 millivolt thermostat cannot be used with baseboard heaters, multi-phase heating systems, and of course, line voltage heating systems.

What I liked
  • The device has no traces of mercury, a dangerous metallic substance.
  • The device has precision measures that maintain the temperature within +/- 1 Fahrenheit of the set level.
  • The switches, buttons, and controls are simple to comprehend and operate.
  • No auxiliary heat source is needed.
  • The warm backlight LCD makes it visible to older people and it can be viewed from across the room.
What I didn't like
  • The thermostat is not compatible with Alexa and Google Assistant, meaning it cannot be controlled via voice commands.
  • The device lacks geofencing technology.
A millivolt thermostat with optional child-lock

The Lux TX9600TS Thermostat has a pretty big display and can be locked with a four-digit password to prevent children from tampering.

Top Features
  • Compatible with most types of 24-volt systems including cooling and heating systems along with millivolt systems.
  • To save battery, users can place the thermostat on vacation hold when they are going on a long journey.
  • The thermostat has an electro-luminescent lighted display coupled with a large display which can be easily viewed without getting too close to the thermostat.

The device comes with a 5-minute programmable time delay for equipment safety.

The 9.8 ounce thermostat has a touchscreen display which is easy to understand and use.  Like Orbit 83521, users can program the temperature of their homes for 7 days (each day can have 2-4 different periods).

Tech Specs

The Lux TX9600TS millivolt thermostat cannot work with 120/240 VAC line-voltage systems without a step-down transformer. The function of a step-down transformer is to lower the induced voltage passing through the secondary coil, reducing the overall output voltage.

What I liked
  • The device has smart recovery features and battery-free memory storage.
  • The device is password enabled.
What I didn't like
  • The device lacks geofencing features.
  • The thermostat is not compatible with Alexa or Google Assistant.
  • There’s no AM or PM indicator on the touchscreen display.

Top Features
  • Smart recovery feature
  • 2 inch square backlit display
  • Retains personalized data after power loss.

The Saswell Single Stage thermostat is a ‘simple but functional’ millivolt thermostat every homeowner needs.

The 8.8 ounce thermostat does not need battery replacement, as long as there’s constant electric power. Users can use two “AA” alkaline batteries to keep the thermostat working during power loss.

What I liked
  • The thermostat can be scheduled for a week.
  • The design is sleek and can fit in every home.
  • The device is simple to understand and operate.
What I didn't like
  • The device is not designed with geofencing tech, an automatic energy saver.
  • There’s no voice control option since the device is not compatible with virtual assistants such as Amazon Alexa and Google Assistant.

Other Millivolt Thermostats

If you’re looking for a millivolt thermostat that does its work efficiently, without expending unnecessary energy, the GEO-WH thermostat is a perfect fit.

Top Features
  • Designed with Geofencing — a program that alerts the thermostat when the user is inside or outside the house.
  • Programmable and easy to install.
  • Compatible with Google Assistant and Amazon Alexa.

A recent app update appears to have caused major issues for users so we'd advise reaching out to Lux before purchasing to ensure the latest version of the app can do what you need

Millivolt thermostats are known for their poor efficiency, as the pilot light (the gas flame that ignites a more powerful gas burner) generally wastes fuel in the long run. 

However, Lux GEO-WH is an exception. The GPS-fortified millivolt thermostat saves energy by using its geofencing feature to regulate the heating or cooling activities of home equipment when the user is inside or outside their home.

Besides its geofencing features, the GEO-WH thermostat can easily be controlled from any location with the aid of a free iOS or Android app.

It can be controlled with voice commands, as well. Users with Alexa, Google assistant or Siri can operate their GEO-WH millivolt thermostat from the comfort of their bed, kitchen or office.

Tech Specs

Like other millivolt thermostats, the GEO-WH millivolt thermostat is not compatible with line voltage systems (120/240 VAC).

What I liked
  • Swift and easy installation coupled with vertical or horizontal mount capability.
  • The device can be powered in two ways: battery or C-wire (aka system power).
  • Users can update their ‘home and away’ status via the app.
  • Saves fuel with the geofencing feature.
  • The thermostat has a large digital display.
What I didn't like
  • Incompatible with heat pump (Y2) two-stage compressor phases.

Top Features
  • Compatibility with heating and cooling systems.
  • Simple design.
  • Weighs 10.4 ounces.

The Braeburn BRA 1220 thermostat is simple to install and use. The device can work with heating and cooling systems. Users can reduce or increase the temperature of their homes.

The 10.4 ounces millivolt thermostat does not require batteries.

What I liked
  • Users don’t need professional skills to install the device.
  • The device is easy to mount. No professional skills or knowledge needed.
What I didn't like
  • No geofencing option.
  • The thermostat cannot be controlled via virtual assistants.
  • Scheduling the thermostat could be difficult for users since there’s no AM or PM indicator on the touchscreen display.

Top Features
  • Flexible programming allows users to schedule the device for 7 days.
  • Easy to use and mount.
  • Smart recovery feature.

Emerson prides itself on making efficient products with easy-to-use interfaces and sleek designs. The Emerson / White Rodgers millivolt thermostat is no different.

The programmable thermostat has an amperage range of 1.5 amps per terminal supporting 2.5 amps total. It has the option of being powered by battery or C-wire.

What I liked
  • The device retains the users’ data after power loss.
What I didn't like
  • The device does not have geofencing features.
  • The thermostat cannot be connected to virtual assistants.

Top Features
  • Simple digital display.
  • Compatible with baseboard heaters.
  • Weighs 1.6 ounces.

For homeowners looking for a thermostat that works with millivolt heating systems and baseboard heaters, the Emerson 1E78-140 millivolt thermostat is a great fit.

The 1.6 ounce thermostat might not be a perfect option for people who would like to schedule their home temperature because the device lacks flexible programming.

What I liked
  • The thermostat is big on precision control, which measures to +/- 1 degree Fahrenheit.
What I didn't like
  • The device cannot be programmed or scheduled by users.
  • The thermostat does not have a time indicator.
  • Comparatively small digital display.
  • The device does not come with geofencing features.

Millivolt Thermostat Features to Consider

While compiling our list of the top 9 millivolt thermostats, we considered the six features given below to be most important.

Programmable schedules

The weather is not always the same throughout the day, so your room temperature may vary between 2-4 periods a day. The best millivolt thermostats are those that can be programmed for each day of the week.

Some thermostats have automatic delay cycles to protect the equipment from overheating. In case your thermostat is not programmed to, you can set a ‘minimum stop time’ which restricts the compressor from restarting too fast after halting.

Easy to use interface

Whether the thermostat is controlled with a touchscreen interface or push buttons, it should be down-to-earth and user-friendly. A complex interface does no good to anyone.

Users should not have to acquire a “special skill”, so to say, before they can enjoy a product. Try to check the users’ reviews to learn from other peoples’ various experiences with the millivolt thermostat you're considering for purchase.

Stylish design

Gone are the days of old boring thermostats. Ever since the Nest thermostats were launched, the bar is now set for these devices to be stylish and fit into the surrounding room decor.

Apart from the device color, the size of the digital display is also a huge factor. The backlight LED color and size of the displayed content contribute to the visibility of the temperature readings.

Users should be able to know the current temperature level by glancing at the thermostat from across the room.

Remote control via smartphone app

Being able to control your millivolt thermostat via the internet is a great feature. Smart thermostats with apps can be controlled from anywhere, as long as the thermostat is connected to the home Wi-Fi or internet connection.  Also, you can use the smartphone app to change the room temperature from the comfort of your bed.

Voice control

Although most millivolt thermostats do not have voice control interfaces, some are compatible with voice control-enabled devices, such as Amazon Alexa, Google Assistant, or Siri.

These virtual assistants can regulate compatible millivolt thermostats when the voice command keywords are mentioned. If most of your home gadgets are connected, you may not like millivolt thermostats that are incompatible with your virtual assistant.

Geofencing to save energy

To avoid unnecessary energy waste, thermostats with geofencing technology reduces the activities of heating and cooling systems when the house is not occupied.

Most geofencing-enabled thermostats have smartphone apps. The app alerts the thermostat(s) when the user gets to the virtual geographic point/boundary created with the aid of GPS technology.

Common Questions Relating to Millivolt Thermostats

What is a millivolt thermostat?

The millivolt thermostat is a self-sustaining thermostat which generates its electrical energy from ‘waste energy’ with the use of a thermopile. The thermopile generator is responsible for the conversion of thermal energy into electrical energy.

The thermopile, which consists of several thermocouples, relies on a ‘pilot light’ for thermal energy. The pilot light is a small gas flame that ignites a larger gas burner.

Like low-voltage thermostats, millivolt thermostats require very low voltage (roughly 0.75 volts). However, unlike low-voltage thermostats, they are usually not dependent on a step-down transformer or external electrical source.

How does a millivolt thermostat work?

Thermostatically controlled loads (TCLs) such as water heaters, gas heaters or air conditioners owe their efficiency to thermostats. The thermostat serves as the brain of these devices.

With the use of sensors, thermostats can detect an increase or decrease in the temperature level of the environment. Most thermostats are able to sense and respond to a change in temperature of a controlled area, such as your home.

The two most important parts of the millivolt thermostat are the sensor and thermopile. The sensor detects an unfavorable increase or decrease in room temperature while the thermopile halts or starts the fuel source of the gas heater in response to the temperature change. 

The thermopile generates electricity from thermal energy with the aim of serial thermocouples. It is important to know that thermocouples can also operate in parallel but more often than not, they are arranged in series.

A millivolt thermostat is common in older structures. Millivolt thermostats can only be used for millivolt heating systems. This guide is for homeowners using gas heaters, wall heaters or floor heaters that are built on the millivolt heating model.  

A millivolt thermostat is not compatible with heaters using line voltage systems.

Unlike other forms of thermostats which are designed to depend on electrical energy from an external circuit, millivolt thermostats are self-sufficient. A millivolt thermostat depends on a built-in thermopile. A thermopile converts thermal energy to electrical energy, so no external source of current is needed.

The Verdict

An intuitive thermostat that is compatible with 750 millivolt and gas fireplaces

While not officially a “smart thermostat”, the T5 has a number of smart features such as learning the heating cycle time of a fireplace or furnace to deliver the correct temperature.

Top Features
  • Temperature limits help save equipment and reduce energy bills.
  • Can be battery powered or hardwired
  • Nice back-lit interface


Show CommentsClose Comments


  • Paul
    Posted December 1, 2021 at 8:02 pm

    You gave this thermostat a top choice review (Lux Wi-Fi Thermostat with Millivolt Compatibility), but when I looked on Amazon I found out that the company was purchased by Johnson controls and created a new app that according to 30% of users doesn’t work. You should look at real user reviews before writing a review article that ignores the real world performance of the product.

    • Daniel Henderson
      Posted December 2, 2021 at 1:45 pm

      Hi Paul,

      Thanks for the message. You are correct in saying that the recent Lux app update has caused major issues for users. We do look at real world reviews however we wrote the article before that app update and haven’t had a chance to review it since.

      I’ve updated the article to reflect the issue and dropped it down the list for future buyers.

      Thanks again


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