Mill Gentle Air oil-filled radiator reviewon November 14, 2023 at 18:16 Tech Advisor

At a glance

Expert’s Rating


Attractive, simple designIntelligent heat control for energy savingQuiet performance


On-radiator controls complicatedSide panels get extremely hot No casters

Our Verdict

The Mill Gentle Air oil-filled radiator is fairly pricey but it’s a great option for people who want to warm up a room that doesn’t have central heating. It’s a quiet and efficient heater with smart features that let you schedule heating and track its energy consumption – and tech to prevent it from overshooting its target temperature and wasting heat.

Scandinavian heating company Mill makes a number of oil-filled, fan and panel radiators that bring together simple, modern designs with energy efficient technology.

They’re designed to waste less heat than the average plug-in radiator. But does it follow that using one will save you money? We put the Mill Gentle Air oil filled radiator to the test.

Design and Build

34.4 x 26.1 x 65.6cm

LED temperature display

The Gentle Air oil-filled radiator comes in 1,000W, 1,500W and 2,000W models. Some have smart features and some don’t, so make sure you’re getting the model you want.

In this review, we’re looking at the 1,500W Wi-Fi model. What’s nice about this radiator is that it has the benefits of both an oil-filled (quiet, efficient) and a fan heater (it vents warm air at the top and heats a room quickly).

The Gentle Air radiator is carefully designed and clearly well made, with rounded corners and a honeycomb air vent. Radiators, fans and the like can create a fair amount of visual clutter and if you have a modern or minimalist home, this is a discreet and attractive option.  

At 34.4 x 26.1 x 65.6cm, it’s slim enough that you should easily be able to find a spot to store it. Beware though: the sides get extremely hot in use and as it’s not on casters, you won’t be able to pick it up until it cools, even though there are nooks in the side to make it easier to lift. It’s fairly heavy too, at 9.9kg.

The hot side panels also mean that you should be careful if you use this heater around small children.

The on-device controls are on one side. There’s a small and not very bright LED temperature display. The display also includes a lightning bolt icon – when it appears, you know that the radiator is using power at that time. It’s surprising how often the icon disappears during a period of use.

Emma Rowley / Foundry

Below the display is the temperature dial and four buttons to adjust heating output, set up Wi-Fi and set a timer. You can also perform more advanced functions, like changing the setback temperature. This last action will mean you can let the temperature drift further from its set point (for example, at night when you’re sleeping and won’t notice a few degrees of difference) to save power.    

Several functions require a sequence of button presses to set up and – even with the manual to hand – I didn’t find it easy to achieve. If you lose the manual, it could be challenging to use some of the on-device controls. But that’s where the smart features come in.

Set Up and Smart Features

Some assembly required

Comprehensive smart features

When you unbox the radiator, the first thing you’ll need to do is assemble it, which amounts to attaching its base. It’s well made, so this is fairly easy as the pre-drilled screw holes line up perfectly. You’ll need a Philips head screwdriver to complete the job.

Then it’s time to set up the smart features. You can use the radiator via its on-device control panel, which makes it useful for guests and anyone in the household who doesn’t want to use the app – although doing anything but the basics is complicated. But half the point of buying this radiator is to use the smart features, so it’s well worth downloading the Mill app (free and available for iOS and Android).

Once you’ve set up an account, the next step is to pair the radiator. You can do this via Bluetooth or Wi-Fi and the app will walk you through the process. Make sure you have your Wi-Fi password to hand.

Everything was straightforward until this point. But when the device connected, it then said a firmware update was required. After that, it said the device was ready to connect. Once the radiator was linked again, we were back at the firmware update. 

After completing the loop three times, the connection was finally made.

Next, you’ll need to create an account. The app requests more information than you really need to provide, including a postcode (for local energy pricing) and phone number (for “important” messages related to Mill products and services).

You don’t need to fill these sections in to use all of the app’s functions, as it provides the heater’s power consumption in kWh. If you know your unit rate, you can work out exactly what it costs you to run. If you don’t know it, you can use an online energy calculator to get an estimate.


The app is much more straightforward than the radiator’s control panel – but that doesn’t mean it can’t do anything complicated. You can see the temperature in the room where the radiator stands and view the radiator’s ongoing power consumption over the current day, month and year. You can schedule the heater to run in several modes, including Comfort, Sleep and Away. And, if you have other Mill devices (heaters, sensors or smart plugs), you can run them via the same app.


Noisy when it starts up

Heat wastage controls

The manual says that it’s normal for the heater to produce “sounds” when it’s first switched on. Those sounds turn out to be a fizzing noise, much like frying eggs. It goes on for a few minutes, so be warned, but it then slows down and stops altogether.

The radiator produces a comfortable heat within minutes and, once the egg-frying noises subside, is perfectly silent in operation.

Mill’s energy-saving claims are based on PID (proportional integral derivative) control, using an algorithm that controls the heater’s output when the room is getting close to the target temperature, so that it never overshoots and wastes energy. It also claims predictive heating and wattage capping capabilities, but these are difficult for us to evaluate on a short-term basis.

On my current tariff, I’d expect a plug-in heater of this wattage (1,500W) to cost around 41p an hour to run – that would be on full power, without any energy saving measures. Over the course of a morning, while it used between 0.06 and 1.235kWh, the Mill heater cost me around 70p and kept the temperature at a comfortable 20°C. If you use it as intended, we think it could save you money. But, like all smart heating systems that offer the promise of saving money on bills, if you’re already frugal and careful with your heat, your savings will be much less.

The radiator has a thermostat range of 5-35°C and overheating protection.

Pricing and Availability

The Mill Gentle Air radiator is fairly expensive. It’s nowhere near Dyson levels, but it’ll cost you much more than your average plug-in appliance to buy. You can buy the 1,500W Wi-Fi model from B&Q for £210 and from Amazon for £194.99.

You can buy it in the US, but the prices are very high, so we opted not to show them above. The 2,000W model is available from Bigamart for $433.99 but we wouldn’t recommend it at this price.

For more plug-in heater options, and to see our top recommendations, have a look at our round-up of the best portable heaters we’ve tested.

Should you buy the Mill Gentle Air oil-filled radiator?

This Mill radiator is the opposite of a fan heater that merrily blasts you with uncontrolled heat and racks up your electricity bill as it does so. Beyond the design, what you’re paying for here is a sensitive thermostat and the technology to finesse the radiator’s output so that it’s never expending more energy than it needs.

If you’re looking for a plug-in heater to use in emergencies or to occasionally top up the heat on the coldest days, it’s probably not worth it. If you don’t use it as intended, you are unlikely to make any energy savings at all. Plus, the on-device controls are confusing at best – we wish they were more user-friendly.

This Mill radiator will come into its own as a regularly used alternative to central heating. If you have a garden office, a dining room or a spare room you only use on occasion, it will provide an efficient way to heat it and to keep track of the energy you’re using.


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