Pellet stove thermostat: which one to choose?
Every pellet stove already has a thermostat: you set a target, it heats until it gets there. The real question is elsewhere: where is the temperature measured, and who decides to light, turn down or stop? There are three answers: the stove's built-in thermostat, an external room thermostat, or an app that controls the stove. Here's what each one does well, and where it stops.
How does a pellet stove's built-in thermostat work?
The stove reads the room temperature with its own sensor, usually mounted on the stove itself or at the end of a cable running from it. It compares that reading to your target, then acts according to its setting:
- with no eco mode, it turns the power down as it nears the target, without stopping on its own in normal running;
- with the eco mode on, it cuts out above one threshold and relights below another. Depending on the electronics, it keeps heating at the set power until that point (this is the case on Fumis-based stoves), or drops to minimum first. These thresholds are adjustable in the stove's own menus, where the manufacturer allows it.
What it does well. It's built in, needs no installation, and works without an internet connection.
Its limits.
- It measures close to the stove. A sensor fixed to the appliance or sitting in its warm air sees a warmer room than the one you're actually in: the stove turns down or stops too early. In a multi-room home, it knows nothing about the other rooms.
- It reacts, it doesn't anticipate. A stove keeps heating after the flame stops: on the one we've been monitoring since February 2026, the room still gains a median 0.6°C over about 70 minutes after cut-out. A thermostat that cuts out exactly at the target ends up overshooting it.
- Its thresholds are fixed. They're the same on a freezing night and on a mild afternoon.
Do you need an external room thermostat?
Most pellet stoves have an input for an external room thermostat, in the form of a dry contact: two terminals that the thermostat closes when heating is needed and opens once the room is up to temperature. Depending on the model and how it's set up, the stove then drops to low power or stops. Your stove's manual spells out this behaviour and where the terminals are.
What it does well.
- It measures where you actually live, not next to the stove. That's its whole point when the stove heats one room and you spend your evenings in another.
- It can be programmable, wireless (a receiver near the stove, the thermostat in the living room) or connected, for remote adjustment.
Its limits.
- It only knows two states, heat or don't heat: it doesn't choose the stove's power.
- It can multiply the number of starts. If the stove stops every time the contact opens, a thermostat with a tight differential makes it relight often, and every ignition wears the igniter.
- It needs installing. Wiring to the terminal block, then setting up the stove's menus: that's a job for an installer.
Can you control a pellet stove's thermostat from your phone?
Once the stove is connected, an app reads its sensor and its status, and sends it the target temperature. It doesn't measure any better than the stove does, since it uses the stove's own sensor. What it changes is who decides, and from what.
In Flam, basic control is free: target temperature, power, the stove's own eco mode, and the weekly schedule on the stove's own timers. Flam Pilot, included in Flam+, goes further:
- Time slots with a target temperature. A slot is a time and a temperature: 20°C from 7 to 9am on weekdays, 21°C in the evening, 20°C at the weekend. As many slots as you want, with no overlap.
- A background temperature outside slots. Between your slots, Flam Pilot holds a lower temperature of your choice, or leaves the stove off.
- Early ignition, with Eco+. For each slot, Flam Pilot works out when to light from the outdoor temperature and your home's inertia, which it learns as it goes, so the room reaches your comfort range at the start of the slot. It's a calculation, not a guarantee: in the first few days it still knows your home poorly, and if it expects to run late, it warns you. A notification also warns you ahead of each preheat.
- A flame that modulates. Eco+ varies the power across the stove's five levels and cuts out with inertia in mind. Depending on the setting: a steadier temperature (Comfort), or fewer ignitions (Economical).
- Safeguards. The number of automatic ignitions is capped each day, every action is logged in a history, and you can take back control at any time.
Its limits too.
- The sensor is still the stove's own. If it's badly placed, Flam inherits its error. When it returns inconsistent readings, Flam pauses its automatic settings and warns you.
- It needs a connection. The stove must be reachable through its module's online service, and you need to give the stove's town: without it, Flam Pilot and Eco+ stay locked.
- Not every stove can be controlled. Flam controls stoves fitted with a Fumis WiRCU module today. The list of compatible pellet stoves says which ones.
Which one should you choose?
- The stove is in the room you live in, and your hours barely change: the stove's own thermostat is enough. Switch on its eco mode if you want to avoid heating for nothing.
- The stove heats one room and you live in another: an external room thermostat measures in the right place.
- You want to come home to a warm house without heating it all day: time slots with a target temperature, and an ignition that adapts to the cold outside, are what an app like Flam Pilot is for.
One last thing to avoid: letting two automations decide at once. An external thermostat opening its contact while an app asks the stove to heat sends it two conflicting commands, so pick the one that's in charge.
Stove control and the weekly schedule are free in Flam. Flam Pilot and Eco+ are part of Flam+, which can be tried for 10 days, no payment card required.