Soldato
Thought this might be of interest, so posting it up. I'd be interested to see if anyone else here is doing the same! 
Background:
I've been on a mission to keep my (detached) garage dehumidified and heated during the winter months. Partially to protect the things I keep in there from getting ruined, partially as I use it as a workshop and things like that from time to time. My initial plan was to install a cheap-ish dessicant dehumidifier, which ended up being a Meaco DD8L. These are good, but the build quality is very suspect and I've repaired a few faults with mine leading me to splash out on a Ecor Pro DH800, which honestly has proved to be crap. The damage humidity does and the efficiency of dehumidifiers is linked to temperature, so I figured if I keep the garage at least slightly warmer than outside (and in any case, definitely above freezing!) and at a reasonably consistent temperature I would overall have a better time of things.
I rigged up 2x 2kW electric heaters to a pair of smart plugs and using HomeAssistant and a smart thermometer I crudely automated a heating solution - on if the temps drop below 5c, off when the temp is above 10c. This worked well but when the ambient temperatures dropped well below the 5c lower target the duty cycle of the heaters was getting to 50% or more, meaning the garage heating was costing somewhere between 60p and £1.20/hr. In October, this cost me about £25. In November, £80 and in December I spent well over £100 in electricity just to heat the garage! I needed a better solution.
The solution!
I joined in with the internet hysteria and picked myself up a Chinese clone of the time-honoured Webasto diesel heater, most commonly used to heat camper vans at night. The patent has expired so there's a million clones of these popping up all over for sale, but I believe the innards are made by just one or two factories and everyone else is just rebadging or repackaging them. I opted for the "Maxpeedingrods" 5kW portable unit. Some claim to be 8kw, that isn't actually possible and as far as I can tell the 5kW and 8kW options are actually identical and by default can only put out around 4.5kW anyway. I bought a portable all-in-one unit rather than an installation type kit purely because it was cheaper! It really pays to shop around with these things as there's a zillion competing brands. I had no intention of keeping it intact as the portable unit so it didn't matter how it came packaged. It might matter to you if you want to go down this path so I recommend doing some research here. My unit cost £89, plus I spent about £20 on some other sundry items.
The way these work is really simple - there's a chamber with a glow plug in it and fuel is sprayed in, where it burns. A fan draws air in through the intake port, draws the burning air/fuel mix through a chamber where it fully burns and then exits through the exhaust port. An external fan (on the same shaft as the internal fan) draws air over the outside of the casing, getting extremely hot in the process. It is this air which heats the space. The exhaust air MUST be ducted EXTERNALLY or you will die of Carbon Monoxide poisoning. As long as that is going outside, the hot air is just the heated air from inside your space and is as safe as that air is already, just hotter.
Where I'd mounted the DH800, I already had a hole drilled in the garage wall so although far from the ideal placement for all sorts of reasons, it meant I didn't have to break the SDS out and put yet another hole in the wall. The layout and siting of the garage in relation to the neighbours plus some other factors ruled out any other wall than the one it has ended up on, so it isn't too bad a compromise. The exhaust fits through the existing hole a little too well, so I have packed some fireproof insulation around it to seal it up.
These units typically come with a 5L fuel tank (although some of the install kits come with a 10L tank) but at ~140ml/hr fuel consumption at the lowest (more on that later), 5L isn't going to last long enough, especially for a mostly unattended setup like mine. Assuming an absolute worst-case situation of it needing to run 24/7, having to refill the tank every single day is just ridiculous. I have taken a standard 25L fuel can, drilled a hole in the lid to take a fuel stand pipe and another to ventilate the tank. Originally this was just a 0.5mm hole but I quickly realised the fuel smell was unbearable even with such a tiny opening. Installing a one-way valve quickly sorted that problem! By doing it this way, I can easily swap out the 25L containers for refilling purposes.
80-85 hours of running in a consistently cold month seems to be a fair estimation of the real-world worst case for MY garage based on the electricity usage I've seen for 4kW of electrical heating. 85 hours at a consumption of 0.2L/hr gives 17L of fuel in a month. If you run it on pump diesel at today's price of 145p/L that's ~£25/month. In actual fact, I am running mine on Kerosene which is £1/l in small quantities from my local supplier, so even cheaper. If you already have Kerosene/fuel oil/Jet A1 delivered in bulk you're probably paying significantly less than that...
There is a slightly unfair comparison here. 0.2L of Kerosene only contains about 2kW of energy so to put it in fair terms, Kerosene is roughly 10p/kWh vs 30p/kWh for electricity. Still an enormous saving, a projected ROI of about 10 wintry weeks.
Next up: Automation. These units are designed to be run from a control panel and there's nothing much in the way of smartness around these units. I've seen some now come with bluetooth and an app but I didn't think these would serve my purposes and in any case they cost a lot more, a route I didn't think was in keeping with the spirit of what I'm trying to do. Instead, I am using an ESP32 board with an STX882 transmitter to emulate the crappy RF remote control that these things come with. This works really well! Initially I was using Tasmota and sending the RF commands via MQTT but I have just switched to ESPhome for a bit of a QoL improvement in HomeAssistant. With that successfully working to turn the heater on/off, I just switched the automation routines away from turning the smart plugs on and off to sending the on or off RF commands. Simples!
I'll take some pictures later on and add them to this post so you can visualise the setup. It isn't pretty at the moment, something I'll work on as time allows but it is at least functional for now
Background:
I've been on a mission to keep my (detached) garage dehumidified and heated during the winter months. Partially to protect the things I keep in there from getting ruined, partially as I use it as a workshop and things like that from time to time. My initial plan was to install a cheap-ish dessicant dehumidifier, which ended up being a Meaco DD8L. These are good, but the build quality is very suspect and I've repaired a few faults with mine leading me to splash out on a Ecor Pro DH800, which honestly has proved to be crap. The damage humidity does and the efficiency of dehumidifiers is linked to temperature, so I figured if I keep the garage at least slightly warmer than outside (and in any case, definitely above freezing!) and at a reasonably consistent temperature I would overall have a better time of things.
I rigged up 2x 2kW electric heaters to a pair of smart plugs and using HomeAssistant and a smart thermometer I crudely automated a heating solution - on if the temps drop below 5c, off when the temp is above 10c. This worked well but when the ambient temperatures dropped well below the 5c lower target the duty cycle of the heaters was getting to 50% or more, meaning the garage heating was costing somewhere between 60p and £1.20/hr. In October, this cost me about £25. In November, £80 and in December I spent well over £100 in electricity just to heat the garage! I needed a better solution.
The solution!
I joined in with the internet hysteria and picked myself up a Chinese clone of the time-honoured Webasto diesel heater, most commonly used to heat camper vans at night. The patent has expired so there's a million clones of these popping up all over for sale, but I believe the innards are made by just one or two factories and everyone else is just rebadging or repackaging them. I opted for the "Maxpeedingrods" 5kW portable unit. Some claim to be 8kw, that isn't actually possible and as far as I can tell the 5kW and 8kW options are actually identical and by default can only put out around 4.5kW anyway. I bought a portable all-in-one unit rather than an installation type kit purely because it was cheaper! It really pays to shop around with these things as there's a zillion competing brands. I had no intention of keeping it intact as the portable unit so it didn't matter how it came packaged. It might matter to you if you want to go down this path so I recommend doing some research here. My unit cost £89, plus I spent about £20 on some other sundry items.
The way these work is really simple - there's a chamber with a glow plug in it and fuel is sprayed in, where it burns. A fan draws air in through the intake port, draws the burning air/fuel mix through a chamber where it fully burns and then exits through the exhaust port. An external fan (on the same shaft as the internal fan) draws air over the outside of the casing, getting extremely hot in the process. It is this air which heats the space. The exhaust air MUST be ducted EXTERNALLY or you will die of Carbon Monoxide poisoning. As long as that is going outside, the hot air is just the heated air from inside your space and is as safe as that air is already, just hotter.
Where I'd mounted the DH800, I already had a hole drilled in the garage wall so although far from the ideal placement for all sorts of reasons, it meant I didn't have to break the SDS out and put yet another hole in the wall. The layout and siting of the garage in relation to the neighbours plus some other factors ruled out any other wall than the one it has ended up on, so it isn't too bad a compromise. The exhaust fits through the existing hole a little too well, so I have packed some fireproof insulation around it to seal it up.
These units typically come with a 5L fuel tank (although some of the install kits come with a 10L tank) but at ~140ml/hr fuel consumption at the lowest (more on that later), 5L isn't going to last long enough, especially for a mostly unattended setup like mine. Assuming an absolute worst-case situation of it needing to run 24/7, having to refill the tank every single day is just ridiculous. I have taken a standard 25L fuel can, drilled a hole in the lid to take a fuel stand pipe and another to ventilate the tank. Originally this was just a 0.5mm hole but I quickly realised the fuel smell was unbearable even with such a tiny opening. Installing a one-way valve quickly sorted that problem! By doing it this way, I can easily swap out the 25L containers for refilling purposes.
80-85 hours of running in a consistently cold month seems to be a fair estimation of the real-world worst case for MY garage based on the electricity usage I've seen for 4kW of electrical heating. 85 hours at a consumption of 0.2L/hr gives 17L of fuel in a month. If you run it on pump diesel at today's price of 145p/L that's ~£25/month. In actual fact, I am running mine on Kerosene which is £1/l in small quantities from my local supplier, so even cheaper. If you already have Kerosene/fuel oil/Jet A1 delivered in bulk you're probably paying significantly less than that...
There is a slightly unfair comparison here. 0.2L of Kerosene only contains about 2kW of energy so to put it in fair terms, Kerosene is roughly 10p/kWh vs 30p/kWh for electricity. Still an enormous saving, a projected ROI of about 10 wintry weeks.
Next up: Automation. These units are designed to be run from a control panel and there's nothing much in the way of smartness around these units. I've seen some now come with bluetooth and an app but I didn't think these would serve my purposes and in any case they cost a lot more, a route I didn't think was in keeping with the spirit of what I'm trying to do. Instead, I am using an ESP32 board with an STX882 transmitter to emulate the crappy RF remote control that these things come with. This works really well! Initially I was using Tasmota and sending the RF commands via MQTT but I have just switched to ESPhome for a bit of a QoL improvement in HomeAssistant. With that successfully working to turn the heater on/off, I just switched the automation routines away from turning the smart plugs on and off to sending the on or off RF commands. Simples!
I'll take some pictures later on and add them to this post so you can visualise the setup. It isn't pretty at the moment, something I'll work on as time allows but it is at least functional for now
