Diesel heaters are cheap to buy, cheap to run and can heat a space quickly. Unsurprisingly they have become very popular. They could be the perfect solution for a garden office, garage, van or tent.
But how do they work, how difficult are they to install, what are the real running costs and are they safe?
I’ve been testing two popular models, the Hcalory TB Max and TB2s+, for the last month or so to heat my garden-office log cabin, which gets very cold – and comparing them to my current electric panel heater setup, which is still expensive to run, even with solar and battery backup.
And the ones I’m testing today are surprisingly techy – they have wireless remote controllers with built-in temperature and carbon-monoxide sensors, and they can even be controlled from a smartphone app over Bluetooth.
So are they really that good? Let’s take a look.
How diesel heaters work
These heaters are very simple in how they work. Diesel is burned inside a metal chamber heating up a set of fins.
A fan blows cool air over these fins and drives clean hot air into your space.
If you want a little more detail, there’s a small pump that drips fuel into the chamber and a glow plug gets very hot to start everything burning. The chamber draws in fresh air for combustion, and there’s an exhaust that dispels fumes safely outside.
These diesel heaters are sometimes referred to as parking heaters, since they were originally designed to keep trucks warm without having to wastefully idle the engine.
They were originally made by two German companies, Eberspächer and Webasto, and they were pretty expensive. But in recent years the designs have been widely copied, and the much cheaper versions — like the ones I’m testing in this article — are often referred to as Chinese diesel heaters.
Installation and setup
You can install these heaters inside or outside your space. Inside will heat your room slightly quicker, but is a little more involved. You need to pull air for the combustion chamber from outside, and you need to run the exhaust outside too. There is also more noise running them inside too – the pump makes a clicking sound. But they have got quieter, one of the models I’ve been testing has an almost silent pump. Also filling the tank with diesel can be smelly – I personally wouldn’t want that in my office space. There are safety concerns too I’ll discuss shortly.
Outside makes the most sense. You only need to run the hot air ducting into your space.
The main issue running it outside is keeping it protected from rain and snow. Some units have weather proofness but you should really keep them covered. I’ll show my final permanent setup later.
They do also need electricity which seemed counter initiative when you first get one. They don’t need much and can run off a 12V supply, but both the models I’m testing have a mains to 12V adapter too. The glow plug that ignites the fuel at startup needs around 120W, and the fans need around 20 W to 40 W continuously.
So outside, you’ll need to run a cable for electricity or you can use a portable power station. This is ideal if you’re camping or in your campervan.
I used the included mains to 12V adapter both via a portable power station and ultimately via an extension lead to an outside AC socket.
They’re super simple to use. Fill the tank with diesel and connect power.
For my initial setup, I just ran the hot-air ducting through a window using the same vent kit I installed for my portable air conditioner – this log cabin also gets unbearably hot in the summer!
The second test unit I permanently installed, drilling a 95mm hole into my cabin wall to install the hot air ducting. I’ll cover that install in more detail later.
On both of my units, you simply press and hold the power button for two seconds to start them up. The startup sequence takes a few minutes while the glow plug heats up, the impeller draws in air for combustion, and the fuel pump starts delivering diesel into the chamber. Once it’s running, you get a steady stream of warm air into your space.
On most heaters, you can then set the temperature level manually between 1 and maximum power HH10. This just controls how often the pump squirts diesel into the combustion chamber. I’ll cover additional ways to control the room temperature when I look at the specific heaters I’m testing.
Real world performance
My initial tests were done on a cold November day. Using my first test unit, installed outside with the hot air ducting running in through a window vent kit.
This is not the ideal setup, but it’s also the most common setup for many people using a diesel heater more casually – in a tent or van for example.
I checked the temperature of the hot air coming into my office with my thermal imaging camera at around 70°C. This remains fairly constant even as you adjust the output level. You just get less hot air at the lower levels.
As I mentioned earlier, the pumps on these heaters are very quiet, especially on my newer unit. The main thing you hear is the rush of hot air, particularly when you’re running at higher output levels. I measured between 48 dB at level 1 and 60 dB at maximum output one metre from the vent on my permanent install.
With my initial tests with the hot air ducting coming through the windows, the outside temperature was 0.3°C and inside my log cabin office it was 5.9°C. With the heater at maximum power after one hour the temperature had reached 12.2°C
After another 3 hours the final temperature in my office was a very warm 21.8°C. The temperature outside was 2.7°C.
I did the same test on another similarly cold day with my 2 kW electric panel heater. The outside temperature was -0.5°C and my office was 4.3°C.
After one hour the temperature in my office was 9°C and after another 3 hours it got to 19.5°C. The outside temperature was warmer though by this time at 7.8°C.
I’ll come to running costs in a minute, but considering the diesel heater is meant to be 8 kW and my panel heater is 2 kW, the diesel heater only performed a little better.
Running costs
My main interest in these diesel heaters are the running costs. I have solar and just under 10 kWh of battery backup. These batteries charge for free via the sun, or are topped up when the electric car is charging at only 7 p per kWh on my Intelligent Octopus Go tariff.
But running my 2 kWh electric panel heater quickly uses any free or cheap energy stored in the batteries, and then I pay 31 p per kWh or 62 p per hour to run the heater.
To work out running costs I ran the diesel heater at full power for 3 hours 50 minutes, measuring the weight of the unit before and after to see how much diesel was used. From this value I could calculate the litres used per hour, and knowing the price of diesel I calculated the running costs.
So the heater burnt 0.42 kg / h which equates to 0.50 L / h. One litre of diesel currently costs £1.44 so at full power the heater costs 72 p / hour.
This is all fairly easy to measure. It’s harder to work out what the real power of the diesel heater is. Both heaters are supposedly 8 kW heaters, but in reality they’re a lot less than that. Diesel fuel has around 10 kWh per litre so the most this heater can produce is actually 5 kW. And if we assume we realistically might get 85% of this theoretical output into my office that’s around 4.25 kW. So the actual cost per kWh is 72 p / 4.25 kWh = 72/4.25 = 17 p / kWh.
In simple terms, at typical settings the diesel heater costs roughly half as much per kWh as my electric panel heater here in the UK. That’s running on diesel – and you might be able to get kerosene cheaper, which these heaters also run on perfectly well.
But diesel heaters typically have 10 output levels so you can regulate the heat a lot better than my panel heater with a low 1 kW and high 2 kW setting.
I ran the same tests at its lowest level 1 and level 3 which worked out 0.10 and 0.14 L / hour respectively. Or 14 p / h at level 1 and 20 p / hour at level 3.
The unit does use a little electricity too but it’s almost negligible. For ignition and shut down where it burns off any excess fuel it uses between 100 and 120 W, but when it’s running it uses a lot less.
Around 14 W at level 1 and 41 W at max power. So typically less than 1 p / hour in electricity.
Safety considerations
Since burning diesel always produces carbon monoxide, you can assume the exhaust also contains carbon monoxide – and my gas meter jumped to over 100 ppm within seconds when placed near the exhaust. Even if the heater is outside, wind can blow fumes back towards the space you’re heating, so you must install a carbon-monoxide monitor.
Both the diesel heaters I’m testing have a remote that has a carbon monoxide monitor built in does work in my testing, but it reacts far more slowly than my standalone detector. It’s a useful backup, but I wouldn’t rely on it as your only protection. I use an X-Sense WiFi carbon monoxide alarm, which can send alerts to my phone.
I also run an AirGradient One air-quality monitor. It’s excellent for tracking CO₂, and it also measures PM2.5 and VOCs, so you can keep an eye on overall indoor air quality while using a diesel heater. I’ll link both the X-Sense alarm and the AirGradient monitor in the description if you’re interested.
Additionally, the exhaust can get very hot – I measured the exhaust pipe with my temperature probe at over 200°C – so make sure no children or animals can come into contact with it, and ensure it’s kept away from anything combustible.
I was concerned I’d smell the diesel heater, but that hasn’t been the case — there’s no noticeable diesel smell in normal use. The only time I noticed anything was from my permanent install through plastic vents. There was a slight smell from the plastic when it first heated up, but that disappeared after a short break-in period.
This isn’t really a safety concern, but diesel heaters do dry the air very effectively. I saw humidity drop to around 45% at times. That may be good or bad depending on your situation, but at that level I found it really dried my eyes.
The heaters I tested and permanent install
Both the heaters I tested are from Hcalory – one of the most popular manufacturers of these heaters and reasonably priced.
My initial tests were on their Toolbox 2S Plus. They recently released the new and upgraded Toolbox Max. Both units are very similar and the 2S Plus is still available and cheaper. They come with the same wireless remote with a built-in temperature gauge and carbon monoxide monitor. They both have the same controller and smartphone app.
The TB Max has a couple of nice upgrades. The pump is a little quieter – it’s not particularly noisy on the 2S Plus but it’s virtually silent on the Max, especially at the higher output levels. More importably it has a weatherproof enclosure, although no official IPX rating. It also has a bigger fuel tank – 7.5 L vs 6 L – and you can see the fuel level on the Max – which wasn’t possible on the 2S Plus without opening it. The combustion air intake is integrated into the TB Max.
On the 2S Plus it has a separate hose, which gets in the way, but does make it easier to install indoors since you need to run both the combustion intake and exhaust outside. On the TB Max you’d have to get creative on the air intake if you wanted to run it indoors.
You can see their dimensions above but the Max is a fair bit deeper. It also doesn’t open up like the 2S Plus so you’ll need to remove a load of screws for servicing.
Check out David McLuckie’s excellent YouTube channel if you want to see how to take these exact machines apart. Although the Max is harder to open, it’s actually more serviceable than the 2S Plus. The user manuals don’t mention servicing, but as long as you let them shut down properly to burn off any excess fuel, they shouldn’t need much attention. And because they’re so basic, if something does go wrong, you should be able to fix it yourself, if you’re handy.
Both come with exhaust hoses, silencers and ducting for the hot air. The hot-air duct is a fairly short 90 mm hose — not the easiest to work with, but it does do the job.
You also get hose clamps and an extension cable for the controller, which has a built-in thermometer if you want to mount it on a wall. The TB Max also has some rubber feet and mounting brackets.
Both come with the same AC to 12V DC adapter and they both also come with a DC cable to connect to a car battery or a portable power station if you attach a suitable connector.
In my tests both heaters do a similar job and although it’s hard to do an exact comparison of their output they’re both rated as 8 kW, and seem to provide the same heat. As I already said, the pump is not exactly noisy on the 2S Plus but on the Max I can barely hear it I have the output level above 3.
The remotes are a little cheap and plasticky but it is very useful to control the unit particularly when it’s outside. You can switch the unit on and off, set the power level in manual mode or switch to automatic mode and set the room temperature. The remote can display its temperature or the temperature of the controller on the diesel heater. Generally you’d go by the temperature on the remote which does read about 1°C lower than my other thermometers and only to the nearest degree. The remote has an integrated battery which always concerns me, but I’ve checked and replacement remotes are available.
After testing various configurations, I ended up installing the newer TB Max outside my office. All you really need to do is drill a hole for the hot-air hose, and Hcalory include a vent for a neat finish. The only issue with this setup is that you’re only blowing hot air in, which slightly pressurises the room. When that happens, the warm air you’ve just heated gets forced out through any gaps in the building. That escaping warm air then has to be replaced – and the heater ends up pulling in cold outside air for its intake, which is less efficient. By pulling the intake air from inside the room instead, the heater recirculates already-warm air, avoids pushing heat out, and warms the space faster while using less fuel.
To achieve this, I attached ducting to the heater’s air inlet. I designed a simple 3D-printed adapter that converts the 90 mm hose to the inlet size, drilled a second 95 mm hole, installed another vent, and connected it to the heater’s intake.
If I’m completely happy with this setup, I’ll make another hole for the power cable, but for now I’ve just plugged it into the outside socket.
I still needed to protect the AC adapter from the elements, and even though the TB Max is supposed to be fine outdoors, I don’t fully trust it’ll survive our wet climate here on Dartmoor. So I cut up an IKEA plastic crate to cover both the heater and the adapter.
It’s not the prettiest solution, but I needed something quickly — and it does the job for the time being. Frustratingly, because the exhaust is on the wrong side for my setup, the heater has to face the wall, so I can’t see the fuel gauge. It seems to be designed for indoor installs, where the gauge would be accessible and the exhaust would go straight out through a wall.
I haven’t had the current setup running long enough to properly compare it with my initial tests, but so far so good. It got the office from 8.3°C to 15.2°C in just one hour. When the colder weather returns, I’ll run some more tests and provide an update in a future article and video.
I have been using the automatic temperature mode with this new setup and it does a decent job. I set the room temperature to 18°C.
It kept the temperature between 17 and 19°C according to my Switchbot temperature gauge. It automatically ramps the levels between 1 and 10 as required.
One thing missing from the Hcalory heaters is Wi-Fi control. The app only offers basic Bluetooth control, which is handy, but you have to be close to the unit for it to work. I can’t, for example, switch the heater on from the house, which is about 20 metres away.You can set a timer for the unit to turn on and off, but it’s very limited. You can’t choose the power level, or pick between manual and automatic mode – it just starts up using whatever the last setting was. It’d be great if Hcalory could update the smartphone app to offer better control.
I’m currently trying to integrate the heater into my Home Assistant setup using ESPHome, but I haven’t got that working yet – I’ll provide an update if I do. But that would sort out both the remote control and the limited timer functionality.
Conclusions
I’m still not super keen about burning diesel, but for my cold garden office these diesel heaters been quite a revelation. They’re cheaper to run and make it far easier to get – and maintain – your space at the right temperature compared to an electric heater. They’re fairly straightforward to set up, not too expensive to buy, and should be mostly maintenance-free if you use them correctly.
There are still a few things to keep in mind. Installing them outside is safer, a little quieter, and avoids having to route a very hot exhaust pipe through your wall. And while there’s no noticeable smell in normal use, refilling them almost always leads to a drip of diesel – which you definitely don’t want indoors. It’s also worth noting that even outside, the rush of air at higher output levels is still quite noisy; I have to turn mine off completely when filming.
A small heat pump would still be cheaper to run and much cleaner overall, but the upfront cost and installation for a garden office are a lot higher – which is why these diesel heaters are so tempting in the first place.
Both of the Hcalory models I tested are pretty good: they heat quickly and are simple to use. However, neither has WiFi, only Bluetooth, the timer functionality is very limited, and there’s no fuel-level readout in the app or on the remote.
If you can stretch to the TB Max, it’s the nicer option: the pump is almost silent, the fuel tank is bigger, and the added weather protection makes outdoor installation more practical. Please check my links below for details and any discount codes I have.
But whichever diesel heater you choose, these heaters can be a practical, lower-cost way to heat a small space. Set them up safely outside — ideally with both intake and output airflow handled properly – and they offer steadier heat and far lower running costs than a basic electric heater. They’re not perfect, but for the right situation, they’re definitely worth considering.
Don’t forget to take a look at my YouTube video at the top of the page, and again please subscribe to my YouTube channel where I’m releasing videos every week on the latest technology and how to get the most out of it. If you tap the bell icon when you subscribe you’ll get a notification as soon as I release a video, and there’ll be a link to my site here for the written article. YouTube is also the best place to leave a comment. I read all of them and respond to as many as I can!
Amazon Links:
HCalory TB Max: https://geni.us/yiyLA Use codes UK: TECHMAN15 US: HCALOMAX for 15% off!
Hcalory TB2S+: https://geni.us/f6SfR
Or check Banggood – may be cheaper:
Hcalory TB Max: https://www.banggood.com/custlink/33v9uZ2CV8?title=HcaloryTBMax
Hcalory TB2S+: https://www.banggood.com/custlink/DvKZ1SMrFn?title=HCaloryTB2S+
Using my links helps my YouTube channel and this website – thank you!
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