Workshop Diesel Heater Update

Some answers to questions from readers

My blog post about installing a Chinese RV diesel heater in my workshop is probably the most popular post visited on my blog. This has been even more so with the present cost of fuel and the onset of winter weather. You can read my original post here and I suggest you read that post first of all to make more sense of what follows.

First let me say that installing the heater was one of the best workshop improvements I ever made. The heater performs very well and quickly gets my working area up to temperature. My opinion needs a bit more defining.

My workshop is contained in what should be the house garage and is roughly 6m x 4m x 2.5m. It is built onto the side of the house and has one outside wall which is an unfilled standard brick cavity. I have covered the garage door with 1″ Cellotex equivalent foam boarding. This was convenient to mount to match the door construction and probably the thickest I could use without impacting on the garage door operation. My wife has provided a door bottom ‘sausage’ muffler filled with polystyrene beads. The door is therefore relatively draft proof but not perfect.

The roof over the workshop is double skin plasterboard and has timber joists with 6″ of fibre wool insulation.

With the current overnight temperatures (-4C) the temperature in the workshop drops to around 15C. The heater is a 5kW branded model but likely to be only 3kW in practice. It takes around 1 hour to get the temperature up to 19 to 20C in the present externally very cold conditions.

Fuel – I use an approximate mix of domestic heating oil (40%) and vehicle diesel (60%). Why do I do this apart from cost saving ? I have read that domestic heating oil does not have sufficient lubrication content to lubricate the demand pump action in the heater. I therefore err on the conservative side and use a mix of the two. I have no idea whether this is fact or fiction. I do not have access to red (Agri) diesel so this is not an option for me to use but clearly would be the cheapest route and would provide the necessary pump lubrication.

I have a 20 litre diesel storage can which I fill at the local garage every 2 or 3 weeks. This is eyeball mix tipped into the heater internal 5 litre tank together with the heating oil which I siphon out of our domestic tank as needed. I would estimate that I use 5 litres of the mix every 3 to 4 days depending on outside temperatures and based on at least an 8 hour day ‘making things to make things’ as my wife calls it. If the heater tank runs dry I find I do not have to re-prime the heater pump but simply refill the tank and switch back on.

The heater controller is the second one I have fitted. The display died on the first one. The controller is easy to use and allows timed operation, set temperatures and live temperature readouts. It is a three wire connection and I had to extend the cable length with a spliced in 3 core section. The OK button cycles round the various display readings and the ON/OFF symbolled button is the lower middle button. The heater needs a single very short press to start the heater up and a longer press to shut it down. Over pressing the ‘start’ leads to an abortive shut down procedure. The left and right arrows increment the various settings selected by the OK button.

The start up current is very high, around 10A at 12V. The choice of power supply is therefore important to be able to sustain this surge. The controller display allows the value of the supply voltage to be checked. The heater once started roars away at full pump speed (a very fast clacking noise) and once at the temperature set point the clicking drops down to a slow tick. There is an icon on the display that mimics the tick. The sound from the ticking is conducted into the workshop via the inlet and outlet air ducts. Like the ticking of a clock, you just get used to it and mentally cancel it out. Both the roaring at switch on and the ticking are louder outside the workshop than inside but these do abate once the heater reaches the set temperature. I am conscious that both the roar and the tick are probably audible with the neighbours but their ground source heat pump is equally audible to us.

The shut down procedure after the long press on the controller button initiates a full bore roar from the heater. I assume this is to burn off accumulated soot in the heater from the slow background tick reached at temperature set point.

As mentioned above the exhaust is noisy. I believe that the choice of silencer affects this. Straight through ones are to be avoided. There is also some discussion about having two in series to reduce the noise further. I have not tried this. Note also that the exhaust does create black soot so I have fitted an aluminium sheet on the wall to protect the brickwork. Standard shower cleaner spray with a bleach content does remove this. The soot plate can be seen in the image below along with the 20 litre top up container.

My prior post about how I installed the heater details the inlet and outlet duct locations. The heat outlet grill is on the workshop wall between my two milling machines. This is not ideal but was the only practical location. The return is under the Myford stand.

The heat outlet has the shortest duct run being almost directly at right angles through the wall from the heater burner outlet. The return duct is located under my Myford lathe stand and is a simply constructed wide mouth housing tapering down to the flexible duct that connects back to the well insulated ducting along the outside wall to the heater. I have fitted a fine gauze mesh over the mouth of the taper to stop debris entering the heater. The image below gives some idea of the construction to fit the available gap under the Myford.

I think I have covered most of the questions asked by readers but feel free to contact me if you need to know anything further. Clearly everyone’s setup is different but for my workshop this is an outstanding and relatively low cost comfort benefit. It also creates dry recirculating air that benefits my equipment.

Links to similar or related post are listed below : –

Winter Warmth – a diesel heater for the workshop

Seems I need a New Plan for Winter

(Note for some reason WordPress has redated this post after I did some edits ..)

We got the electric bill for last winter and there was a sharp intake of breath … maybe the fan heater had been on too much in the workshop and maybe I did forgot to switch it off once or twice when going to bed …  something had to change.

I did some research on diesel heaters as used in motor homes and commercial vehicles and the concept looked like it would meet my needs.  I did some calculations on the workshop volume I needed to heat as an empty shell.  With my insulation and window content this came to a figure of 3kW.   Searching on EBay revealed lots of kits and ready built units so my first thought was to order a ready built one.  This duly arrived and I decided to run it up to see what happened.

Actually nothing really happened.

The fan came on ran for a few seconds and then the unit shut down.   The controller was showing a severe droop on the supply volts even thought the PSU was rated at 10A.   More web reading and comparing notes with other users revealed these units take a serious current surge at switch on while the glow plug is warming up.   If it sees a voltage droop it thinks it is in a vehicle and switches off to protect the vehicle supply.

Bigger power supply acquired and plugged in.   Still no joy.   I then realised I needed to prime the fuel line.    Quite a few clicks of the pump later I had a full pipe feeding the device and finally it ran up.   The fan was flat out and the pump was clicking like a French grenouille on heat.

And what a stink it made.   I guess it was burning off all the manufacturing oils but it was pretty acrid.   Finally the fog cleared and I could see the neighbours house and we had heat.  Quite a lot of heat.   Fiddling with the pump rate brought the heat and the fan rate down and all seemed good.   But it was noisy.

There now followed some serious navel contemplation.  Did I really want this fire breathing Smaug inside the workshop ?   Not really.   So how to solve the installation ?

Immediate thought was to mount the unit external on the side wall and feed the warm air from the unit into the workshop and take in air from the outside to warm.   The smelly exhaust inlet and outlet would also then be outside.   Not a good idea taking outside air and warming it unless I wanted a very rust rich environment.

So air would have to circulate from the workshop, get heated and blown back inside.  This means two 80mm holes in the workshop wall plus a power and controller wiring duct of say 20mm.   A plan was forming and I could see where the two air ducts could be located.

Next problem the (I have to say very horrible) enclosure my ready made heater came in would not protect the contents nor would it last very long sat in the outside air.

 

original heater enclosure as bought

New Enclosure

Much Fusion 360 playing later I had a design based on a 20mm angle iron frame and aluminium sheet covering.

diesel heater enclosure fusion 360 model
Original Fusion 360 model of the enclosure frame less the two top bracing steels

The angle iron and sheet were ordered from Aluminium Warehouse and came very quickly.   I was now going to have to grasp the nettle and refresh my TIG welding knowledge to create my first major TIG construction.   (I only have TIG as MIG scares the **** out of me).

Even though I say it myself I was pretty chuffed with the frame that resulted.  Some of the welds were far from ticketable but my angle grinder and Hammerite paint soon covered up my ineptitude.

diesel heater angle iron frame
TIG welded heater angle iron frame after clean up and painting

The aluminium covers also stretched my resources as I don’t have a formal metal bender but I do have some very long lengths of angle iron and a robust vice.   Two side walls, a front panel and drop on top cover resulted without any serious clangs.  Loving it.

The return air inlet needed an interface of some sort so a Fusion model was created and printed (6 hour print …).

3D printed diesel heater 80mm air inlet cowl
3D printed diesel heater 80mm air inlet cowl which took 6 hours to print

With the enclosure complete, I mounted all the components and ran it up again.   The new power supply also failed to do the biz so I decided to go with a meatier version inside the workshop rather than inside the external cabinet.

Installation day loomed.   I was very ably assisted by Dave who is a long time friend.   We are both cut from the same engineering mould and we usually end up with an interactive plan of action.

First job was to cut the hot air duct hole in the workshop wall.   We had a long pilot drill, an EBay 80mm cutter and a SDS drill.   Serious grief.   The workshop outside brickwork  seemed to have a Titanium content.   We finally broke through into the cavity and thereafter the inner Thermalite block was like cutting chocolate cake in comparison.   First hole finished and more to the point in the correct position.

We now offered the unit to the wall to match the routing of the hot air outlet pipe of the heater.   We put a car jack under the unit to keep it in position while we drilled the mounting holes.  Holes drilled, we then mounted it on the wall and drilled the cable duct and lined it with a piece of uPVC water pipe.

diesel heater enclosure mounted on the workshop outside wall
Re-boxed diesel heater enclosure mounted on the workshop outside wall.  The pumps is enclosed in some foam to deaden the clicks.

The circulating return air from the workshop was to come through the workshop wall and back to the heater from just over a meter away.    I had a suitable length of 80mm spiral metal ducting for the air return and a mating right angle joint to route this through the wall.   We marked off the duct hole position and drilled out a second 80mm hole (more grief, less dust as we damped it down, and hammer and chisel when we got fed up with the useless 80mm cutter).

The Cunning Plan

I didn’t want the metal spiral ducting exposed to the elements and also saw it as a source of heat loss.   There is no point in heating up the workshop and then send the warmer air outside to lose heat on its way back to the heater.   The solution was to buy a standard 1m length of 110mm soil pipe and a right angle joint with two mounting clips from Wickes.   We wrapped the 80mm spiral duct in bubble wrap (quite a few turns) to fill the space inside the 110mm soil pipe to make a coaxial structure.    As luck would have it the spacing to the wall of the soil pipe was pretty much ideal to use the standard pipe clips.   We did however have to cut down the right angle soil pipe connector to get it flush to the wall.  It then got a dose of squirty foam to seal it.

Finished diesel heater enclosure with coaxial inlet duct
Finished diesel heater enclosure with coaxial inlet duct using 110mm soil pipework and fittings. The 80mm internal duct is wrapped in bubble wrap.

We were both very pleased with the result.   As Dave commented it looked better than a professional install would have done.

This was the bulk of outside work done apart from mounting the exhaust inlet and outlet pipes.   Inside we had the hot in wall vent grill to fix and the controller wiring.

I still haven’t decided where to route the outward air duct but currently it sits sucking air from under the Myford Super 7 cabinet.   I am not comfortable with this (the location rather than the potential draft around my ankles) as it will tend to suck up workshop dust and particles.   Some form of filter will be needed.   As yet I haven’t mounted the new power supply on the inside wall.

We ran it up and I can describe it as toasty warm.   At least one good reason to look forward to winter, probably the only one.

Finally thanks to Dave for helping.  Also thanks to Steve Niebel for detailing his experiences with a similar unit.

If you want to know more about the heaters then the best source I found on YouTube was Dave McK 47

Anyone wanting a very basic indoor housing for their heater components should send me a message ….. and soon …. otherwise it is going in a skip (but I might save the handles).

Update December 2021

The heater has now been installed and running for over 2 years.  It is excellent in making the workshop more than comfortable in winter months.   A few comments to address feedback I have had on this post : –

The controller cable was extended into the workshop by simply cutting the supplied cable and splicing in an extension length of 3 core cable.

I now run a mix of diesel and household heating oil (approx 50/50) which does not seem to degrade performance.  That being said the brickwork near the exhaust is now somewhat black from the fumes.   I don’t get any smell in the workshop with the pipework routing as described.

Fuel consumption is around 5 litres per week if I run it every day for four hours.

I fitted a simple mesh filter over the air intake which remains located under the Myford stand.

With hindsight there is more than enough hot air generated that I could have branched the feed to my office next to the workshop.

Overall this was probably one of my best projects for the knock on benefit.

There is a further update in December 2022 as a new post here.

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