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Best Smart Heating Controls for a Granny Annexe With Its Own Boiler
An annexe with its own boiler is a separate heating zone, and the right control depends on what that boiler actually drives. The five picks below cover a budget Wi-Fi thermostat for a simple combi setup, two knob-style boiler controllers for easy wall operation, a premium floor-heating option, and a system controller for Rheem equipment. Buyers fitting out a small self-contained annexe, landlords future-proofing a rental unit, or families wiring a granny flat to run independently should start with the overview table, then read the one pick that matches the boiler type.
Overview of the Picks
| Product | Key Spec | Best Use | Price Tier |
|---|---|---|---|
| 95 to 240V WiFi Smart Thermostat | 95–240V wide input, programmable | Simple combi boiler on a budget | Budget |
| Rheem RETST800SYS EcoNet Control Center | Rheem EcoNet system controller | Rheem boiler or HVAC equipment | Premium |
| Smart Boiler Thermostat with Tuya App Control | Knob control plus Tuya app, °C/°F | Hands-on wall control with app backup | Mid-range |
| Smart Boiler Thermostat, Wireless Programmable | Wireless programmable, app remote | Retrofit where wiring is awkward | Mid-range |
| SunTouch SunStat ConnectPlus | 4.3" touchscreen, floor and air sensing | Underfloor heating in the annexe | Premium |
1. 95 to 240V WiFi Smart Thermostat
Type: Programmable Wi-Fi boiler thermostat
Voltage: 95 to 240V
Colour: Black
Control: Wi-Fi app, programmable schedule
Best For: Budget annexe heating
The wide 95 to 240V input is the headline here: the same unit suits different supply arrangements, which matters when an annexe has been wired separately from the main house. Programming runs through the Wi-Fi app, so a schedule can be set once and left to run a small, rarely changing space. The black finish is neutral enough for a hallway or utility wall, and the boiler-heating focus keeps the wiring simple.
This is the pick for a straightforward combi boiler feeding a handful of radiators in a compact annexe. It earns its place on price and flexibility rather than polish. Trade-off: at this price tier the housing and display are likely to feel functional rather than refined, and app-only scheduling means anyone without a smartphone will struggle.
2. Rheem RETST800SYS EcoNet Control Center
Type: EcoNet system control center
Brand system: Rheem
Function: Equipment control and monitoring hub
Best For: Rheem-equipped annexes
Rheem RETST800SYS EcoNet Control Center
This is a control center rather than a standalone thermostat, and it only makes sense inside the Rheem EcoNet ecosystem. Where the annexe’s boiler or heating equipment is Rheem and EcoNet-compatible, this unit ties that equipment into one control point instead of leaving it on a basic dial. Build and finish are aimed at permanent wall mounting in a plant room or utility space.
It earns its place for buyers who already own Rheem equipment and want proper system-level control rather than a generic third-party thermostat. Trade-off: it is expensive and effectively locked to Rheem hardware, so it is the wrong buy for any other boiler brand.
3. Smart Boiler Thermostat with Tuya App Control
Type: Programmable knob thermostat
Control: Physical knob plus Tuya app
Schedule: Programmable heating periods
Units: Celsius and Fahrenheit switching
Best For: Mixed users who want a dial and an app
The dual control is the point of this model: a precise physical knob for quick changes at the wall, plus the Tuya app for remote temperature adjustments and scheduled heating periods. That combination suits an annexe shared by people with different comfort levels with technology. Celsius and Fahrenheit switching is a small touch that helps in mixed-household setups.
It suits an annexe where an older relative wants to turn a dial and a family member wants to check the heating remotely. Trade-off: Tuya app control depends on the annexe having a stable Wi-Fi signal, and a boiler room or thick annexe wall can weaken that link.
4. Smart Boiler Thermostat, Wireless Programmable
Type: Wireless programmable thermostat
Control: App remote control plus knob adjustment
Schedule: Scheduled heating
Best For: Retrofits with awkward wiring
The wireless design is what separates this from the wired boiler thermostats above: the control can be sited where it is actually useful rather than where a cable already runs. App remote control and scheduled heating cover the everyday jobs, and the knob keeps basic operation familiar. It is aimed at room comfort in a single zone, which is exactly what a self-contained annexe is.
This is the pick when the annexe’s boiler position makes running new thermostat cable painful. Trade-off: wireless units rely on their own radio link and batteries, so a dead battery or a dropped pairing is a maintenance point that wired models do not have.
5. SunTouch SunStat ConnectPlus Smart Wi-Fi Floor Heating Thermostat
Type: Smart Wi-Fi floor heating thermostat
Screen: 4.3 inch touchscreen
Voice: Alexa and Google compatible
Sensing: Floor and air
App: Watts Home app with energy monitoring
Best For: Underfloor heating zones
This is a dedicated floor heating control, not a general boiler thermostat, and the dual floor-and-air sensing is what makes it worth the money. The 4.3 inch touchscreen makes setup and schedule editing far easier than a dial, and the Watts Home app adds remote access and energy monitoring. Alexa and Google compatibility lets voice control handle the basics.
It earns its place in an annexe with an electrically heated floor in a bathroom or living area. Trade-off: it is the most expensive pick here and is built for floor heating circuits, so it will not control a conventional radiator boiler.
Before You Buy
- Boiler compatibility: confirm the thermostat is rated for the annexe boiler type, and check whether the boiler needs a volt-free or mains switching connection.
- Power and wiring: a wide-voltage model like the 95 to 240V unit copes with more supply arrangements, while wireless models avoid new cable runs entirely.
- Heating type: floor heating needs a floor-sensing thermostat, while radiators and combi boilers need a boiler thermostat — the two are not interchangeable.
- Ecosystem lock-in: system controllers such as the Rheem EcoNet only make sense with matching equipment.
- App dependency: every smart pick here leans on Wi-Fi and a phone app, so check signal strength at the annexe before committing.
- Who will use it: a physical knob helps less tech-confident occupants, while app scheduling suits remote management.
Frequently Asked Questions
-
Can a granny annexe have its own heating controls?
Yes, provided the annexe has its own boiler or heating zone. A separate thermostat on that zone lets the annexe run on its own schedule without affecting the main house. -
Which pick is best for a simple combi boiler?
The 95 to 240V WiFi Smart Thermostat is the budget choice, while the wireless programmable model suits retrofits where new cable is difficult. -
Do these thermostats need Wi-Fi?
The smart models rely on Wi-Fi for app control and scheduling. Without a signal in the annexe, the knob and on-unit controls still work but remote features do not. -
Can one control both radiators and underfloor heating?
Not usually. The SunTouch model is built for floor heating circuits, and the boiler thermostats are built for radiator or combi systems. -
Is a system controller like the Rheem EcoNet worth it?
Only where the annexe already runs Rheem EcoNet-compatible equipment. For other boiler brands it adds cost without adding control.
Bottom Line
For most annexes with their own combi boiler, the 95 to 240V WiFi Smart Thermostat is the fastest, cheapest route to scheduled, app-controlled heating, and its wide voltage input keeps installation flexible. Buyers who want a dial for daily use should step up to the Tuya knob model, and anyone with underfloor heating should go straight to the SunTouch.
