The Mr. Heater F210359 is the manufacturer-listed thermostat for the Big Maxx series. Mr. Heater gives it a 35–75°F setting range. Wi-Fi control may also be an option for some models: the MHU125 product page recommends a 24V thermostat and says that model accepts Wi-Fi thermostats. Check the documentation and wiring diagram for your exact heater before choosing a third-party thermostat.
Which thermostat works with a Mr. Heater Big Maxx?
Start with the Mr. Heater F210359 thermostat. The manufacturer lists it as compatible with the Big Maxx series and specifies a 35–75°F setting range. The listing describes it as a low-voltage thermostat compatible with natural gas and propane heaters.
For another option, verify compatibility against the exact heater model—not just the Big Maxx name. The MHU125 product page recommends a 24V thermostat and says the MHU125 accepts Wi-Fi thermostats. That model-specific statement does not establish that every third-party Wi-Fi thermostat works with every Big Maxx heater.
How to choose a thermostat
- Confirm model compatibility: Look for an explicit listing for your heater or confirmation in its manual. Do not assume compatibility based on a different Big Maxx model.
- Choose the control type: The F210359 is the manufacturer-listed basic option. Consider Wi-Fi control only if your exact model’s documentation supports it.
- Check wiring needs: The manual’s examples use R and W for analog thermostats, and R, W, and C for digital or Wi-Fi thermostats. Confirm the required terminals against your heater’s wiring diagram and the thermostat specifications.
- Match the temperature range to your use: The F210359’s stated range is 35–75°F; check the range of any alternative against your intended operating conditions.
What the wiring instructions say
The Mr. Heater Compact Unit / Utility Heater manual recommends 18 AWG thermostat wire. Its diagrams show analog wiring to R and W, or digital/Wi-Fi wiring to R, W, and C. Use the wiring diagram for your exact model; the manual covers particular heaters and should not be assumed to apply to every Big Maxx variant.
#1 Best Overall
- Programmable
The manual explicitly warns: “DO NOT CONNECT LINE POWER TO THE THERMOSTAT TERMINAL STRIP.” Keep line voltage off the thermostat terminal strip. The manual also says the heaters it covers are designed to be installed and serviced by licensed, trained professionals. If the correct wiring or model-specific instructions are unclear, have a qualified professional handle the work.
If the heater does not respond to the thermostat
Mr. Heater’s Unit/Utility heater support page advises checking the thermostat connection and looking for a broken thermostat wire. It also describes joining the thermostat wires after disconnecting them from the thermostat as a way to help determine whether the thermostat is faulty if the heater then runs. Treat that as manufacturer troubleshooting guidance, not as a replacement for safe servicing or the instructions for your exact heater. If you are not qualified to perform the check safely, contact a licensed professional.
Quick Recap
Best Value
- EASY OPERATION - Aowel 1H/1C Non-Programmable Manual Thermostat. Equipped with Heat/Off/Cool modes, no complex settings required. User-friendly design suitable for all ages. Minimalist white body matches most home decor. Compact size: 4.92 × 3.74 × 0.98 in (W×H×D) for flexible wall mounting.
- COMPATIBLE SYSTEMS - Works with 24v conventional single-stage 1H/1C systems, including forced air (gas, oil & electric), ventilation and air conditioners. 【Please confirm your HVAC system type before purchasing.】
- NOT APPLICABLE UNITS - Not applicable for 2H/1C, 2H/2C, 3H/2C, 4H/2C multi-stage systems & heat pump systems (with aux or emergency heat); PTAC units; 3-wire hydronic heating and dual fuel systems; Not applicable for (120-240V line voltage heaters); mini-split heat pumps; Mach/Roughneck series RV air conditioners.
- NO C-WIRE REQUIRED & DIY INSTALL - Dual power supply design: runs on 24VAC hardwired power or 2 AAA batteries (batteries not included). . Comes with standard RH, RC, W, Y, G, C terminals. 【Does not support W2, W3, Y2, O/B, W/E, L, AUX, ACC+, ACC-, S, X, X2 terminals. 】Use 18-22 gauge thermostat wire. Easy to install by yourself.
- PRECISE TEMPERATURE - Features a 5.0 sq. in backlit LCD screen for clear display (Manual key activates backlight). Temperature accuracy: ±1°F; adjustable temperature swing: 0.2°F to 2°F; manual calibration range: -4°F to +4°F. Display range: 32°F to 99°F; control range: 44°F to 90°F.
Rank #4
- Easy-to-read digital display with backlight
- Non-programmable thermostat
- Compatible with single stage heat only systems
- Precision control of plus/minus 1 degree F
- Vertical profile
Rank #3
- 【Notice】Buyers should thoroughly examine the installation and wiring instructions depicted in the images before buying. It is recommended to exercise caution if you lack experience in installation to avoid potential problems like product malfunction or incompatibility due to incorrect purchases. Note that the base can only be attached with a maximum of 2 to 5 wires, and connections with 6 to 8 wires are not suitable.
- 【Incompatible Systems】Multistage Heat & Cooling, 3-wire Hydronic (Hot Water), Heat Pump with Auxiliary Heating, Heat Pump w/o Auxiliary Heating, Dual Fuel/Hybrid Multistage Heating, Mini Split Systems, RV Thermostat, Convectors/Radiant Ceiling Heat and Electric Baseboard Heat ( 120-240 Volts)
- 【Compatible Systems】Single-Stage Heating & Cooling, Gas/Oil/Electric Furnace (Heat only) , Boiler Radiant (Heat only), Furnace Forced-Air (Heat Only), Gas Fireplace (24 Volts), Cooling Only
- S3001-White Non-programmable thermostat for house conventional single-stage systems up to 1 heat/1 cool, to control the temperature in a room.
- Easy to Install and Use: Large terminal blocks with universal sub-base, can be installed within 30 minutes, clear, easy-to-read backlight LCD display and easy controls make for a user-friendly experience.
Rank #2
- Adjustable Temperature Scale: Standard Selection Of 40 To 90F
- Backlit Display Is Easy To Read
- Displays Ambient (Measured) Temperature At All Times.
- Brand Name: Honeywell
- Power source type: Battery Powered
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.
