There is no single outdoor temperature that works as a heat-on signal for every home. Turn on the heat when indoor conditions become uncomfortably cold or the room temperature is falling below a comfortable, safe level. The home’s insulation, air leakage, heating system and the people living in it all affect that decision.
Use indoor temperature—not the outdoor forecast—as your guide
The World Health Organization’s Housing and Health Guidelines recommend a minimum indoor temperature of 18°C (64.4°F). That is indoor guidance, not an outdoor temperature for switching on a furnace or heat pump.
The U.S. Department of Energy says 68°F can be comfortable in newer, tighter homes, while recognizing that people can adjust settings for personal comfort. This is a contextual comfort example, not a universal health threshold or a rule for every building. The WHO and DOE figures describe different kinds of guidance, so they should not be treated as one mandatory thermostat setting.
Why the same outdoor temperature feels different in different homes
Outdoor air temperature is only one part of how quickly a home loses heat. Insulation, air leaks, the building’s construction and the heating system’s capacity all matter. A tighter, well-insulated home may stay comfortable longer than a drafty home in the same weather; household members may also prefer different indoor temperatures.
#1 Best Overall
- 【Notice】Please make sure to read the installation and wiring instructions provided in the pictures carefully before buying. If you are inexperienced with installation, it is advised to be cautious when making a purchase to avoid issues like product failure or incompatibility. (Verify the existing base to ensure only 2 to 5 wires are compatible for installation and wiring).
- 【Thermostat Applications 1H/1C】for with Conventional Single-Stage Heating & Air Conditioning, up to 1 Heat and 1 Cool. Gas/Oil/Electric Furnace (Heat only), Boiler Radiant (Heat only), Furnace Forced-Air (Heat Only), Gas Fireplace (24 Volts), Cooling Only, Only 1H/1C Heat Pump (without aux) Systems.
- 【Incompatible Systems】Does not work multistage systems (1H/2C, 2H/2C), HVAC heat pump systems (2H/1C, 4H/2C), PTACs, 3-wire hydronic (hot water), dual fuel/hybrid heating. Does not work line voltage systems (120-240V electric baseboards heat); mini split heat pump air conditioner, RV air conditioners mach and roughneck series.
- Suuwer S705 5-1-1 day programmable thermostat 1 Heat/ 1 Cool. Separate programs for the weekdays and weekends with 4 program periods per day including wake, leave, return and sleep.
- 【Technical support】 Separate heat or cool swing set up (0.2°F to 2°F) and 5 minute compressor delay protection (Selectable ON or OFF). Digital thermostat has a built-in battery change and filter change reminders (Set 50-2000 hours)
If you are unsure how cold the rooms are, an indoor thermometer can help you check rather than relying on how the weather feels outside. Set the thermostat to a level that keeps the home comfortable, taking the WHO’s 18°C minimum indoor recommendation into account.
Setbacks and thermostats are optional tools
The Department of Energy suggests considering thermostat setbacks during common periods when the home is vacant. A programmable or smart thermostat can schedule heating settings, and some models allow remote adjustments. ENERGY STAR advises checking that a smart thermostat is compatible with your heating system before buying one. Neither a smart thermostat nor a particular schedule is necessary to decide when your home needs heat.
Rank #2
- PRIVACY PROTECTION*: Sensi won’t sell your personal information to third parties
- EASY DIY INSTALLATION: Use the built-in level and step-by-step app instructions for a quick installation. Works with HVAC equipment found in most homes. Common wire (c-wire) is not required in most applications
- SAVE ABOUT 23% ON HVAC ENERGY*: The ENERGY STAR-certified Sensi smart thermostat can help you save energy with features like flexible scheduling, remote access and usage reports
- SIMPLE CONFIGURATION: Looks and feels like a thermostat. Has buttons and fits the same space as a traditional thermostat so you don’t have to patch and paint your walls
- SMART MAINTENANCE: Sensi can help monitor the performance and efficiency of your HVAC system by delivering valuable usage reports, alerts about your equipment, and maintenance reminders like filter replacement
Heat pumps and cold-weather operation
A heat pump’s useful operating range depends on the specific equipment and installation. ENERGY STAR says certified cold-climate air-source heat pumps are tested for performance down to 5°F. That figure describes a testing point for those certified systems; it is not a universal outdoor temperature for turning on heat or switching to backup heat. Follow the guidance for your equipment, and ask a qualified contractor about system sizing and backup arrangements for your home.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Use supplemental heaters safely
If you use a portable space heater while adjusting your home’s main heating, follow the manufacturer’s directions and keep the heater at least three feet from anything that can burn. The CDC’s winter-storm safety guidance warns: “Turning on the stove for heat is not safe!” Do not use a stove to heat your home.
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Best Value
- An Alexa thermostat - Amazon Smart Thermostat is an easy way to switch from a traditional thermostats for homes and help reduce energy usage.
- Create comfort zones throughout your home by connecting to select Alexa devices to automatically adjust heating and cooling based on temperature readings or presence detection.
- Save money and energy - After purchase, Amazon will send you an email with details about home thermostat rebates that may be available from energy providers in your area.
- Save energy - According to EPA estimates, ENERGY STAR certified thermostats save an average of $90 on yearly energy bills.
- Programmable thermostat and automatic control - Create your own home, away and sleep schedules, or have Alexa automatically control the temperature with Alexa+ advanced features.
Rank #4
- Simple Manual Operation: Heagstat H705 1 Heat/1 Cool, 5-1-1Day Programmable Thermostat (Separate programs for the weekdays and weekends with 4 program periods per day including wake, leave, return and sleep). The user-friendly design is easy to operate for people of all ages
- System Compatibility: Works with conventional single-stage systems, including Forced air (gas, oil, or electric) & Ventilation & Air Conditioning. It supports up to 1 heating stage and 1 cooling stage. Please confirm your home HVAC system type before purchase to ensure full compatibility
- System Limitations: This unit does NOT work with multi-stage systems and heat pump systems (2H/1C, 2H/2C, 3H/2C, 4H/2C: Multi-Stage Heating & Cooling), PTAC units (Packaged Terminal Air Conditioners), 3-wire hydronic hot water heating systems, dual fuel/hybrid heating systems, 120-240V line voltage systems and electric baseboard heaters, mini-split heat pump air conditioners, and RV air conditioners (Mach/Roughneck series)
- No C-Wire Required Design: Dual power supply design runs on 24VAC hardwired power or 2 AAA batteries (batteries not included). Equipped with standard RH, RC, W, Y, G and C terminals. Wire Specs: Use 18-22 gauge thermostat wire. Shielded wire is not required. Easy DIY installation without professional help. It does not support W2, Y2, O/B, E, L, AUX, ACC+, ACC-, S, X and X2 terminals
- Clear & Easy-to-Read Display: Minimalist off-white body matches most home interior styles. The 4.5 sq inch backlit LCD screen delivers clear visibility under all lighting conditions. Compact dimension: 0.98 inches D x 4.72 inches W x 3.86 inches H, allowing flexible wall mounting
Rank #3
- · High Compatibility: Forced air (gas, oil or electric), Electric furnace, Hot water steam or gravity radiant heat, Heat only systems, Heat pump w/o auxiliary or emergency heat, Millivolt, Gas fireplaces (24V), Floor or wall furnaces, Cool only systems.(TIP: Before purchasing, check to see if this thermostat is compatible with your system.)
- · Not Compatible: Heat pump with auxiliary or emergency heat, Dual fuel/hybrid heating, Electric baseboard heat (110-240 volts), Line voltage, Convectors, Radiant-ceiling heat, Mini split systems and 12V RV systems.
- · Easy to Install and Use: Large terminal blocks with universal sub-base, can be installed within 30 minutes, Large, clear, easy-to-read backlight LCD display and easy controls make for a user-friendly experience.
- · Factory Pre-set Energy-efficiency Program: 7-day, 5/1/1 easy-to-understand programming menus, flexible programming lets you sync your comfort with your schedule.
- · Reliability: Made by professional manufacturer and backed by over 20 years of experience, the customer service is 7*24 hrs available.
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.
