Small Diesel Shop Heater

[DAPPH]

The exposed exhaust on the bottom of the heater gets hotter than the body of the heater.

True , but as I can hold the burner air inlet tube and the fuel line just below the heater body after it's been running for four hours today so I'm not too worried .

 

[qwakers]

and what about the exhaust?

 

[DAPPH]

so any fresh air coming into the building will be cold therefore defeating your intention

its better to take fresh clean air from outside pipe it through the burning system and back out

The cool fresh air is pipe directly into the inlet of the heat exchanger, if you notice in my pictures there is about 400 mm of ribbed 100 mm ID aluminium duct and stainless tube for it to pass along before it enters the heat exchanger , so I'm not hung up with the idea of a few lost joules of heat .
The mancupboard is well toasty warm at 15 oC on setting H 1 , having it on H 6 would be way too hot for me .

 

[gaz1]

if you was to run the exhaust down the middle of a wider tube then the incoming air would be preheated by the exhaust pipe thats going out

thats how the boiler flues work as well as the corvec britonys

 

[gaz1]

The cool fresh air is pipe directly into the inlet of the heat exchanger, if you notice in my pictures there is about 400 mm of ribbed 100 mm ID aluminium duct and stainless tube for it to pass along before it enters the heat exchanger , so I'm not hung up with the idea of a few lost joules of heat .
The mancupboard is well toasty warm at 15 oC on setting H 1 , having it on H 6 would be way too hot for me .

yours is set right so the coment wasnt for you it was for the poster saying the air is best taken from inside of the building then goes through the burner then out

which is not a good way for any stove if your spray painting, wood stoves being the worst as they take more air from within the building to be burnt and sent up the chimney

 

[DAPPH]

and what about the exhaust?

I guess that the expelled exhaust gasses are not hot enough to melt the casting housing exhaust spigot as the heat exchanger cooling holds the temp safely well below that ( 230 oC seems to ring a bell ) If it gets too hot the 230 oC maximum the heater goes into auto shut down , I suspect that the casing metals melt at around 660 oC plus . None of the stripped down heaters I've seen on a dozen or more Your Tube videos have had any melting take place .

I had thought of making a simple stainless steel wire mesh heat shield from some off cuts I've got , to stop accidental touching of the hot pipe before it goes out the wall . On the outside where the silencer is I can hold my hand on the silencer quite happily as it is barely warm on H 1,2 & 3 settings. It is a tad to hot to do that on the exhaust silencer if I turn the heater up to the H 6 setting .

 

[DAPPH]

if you was to run the exhaust down the middle of a wider tube then the incoming air would be preheated by the exhaust pipe thats going out

thats how the boiler flues work as well as the corvec britonys

Yes I know of the balanced flue & heat exchanger systems and did consider doing just as you suggest as I have the old balanced flue system from a previous oil fired boiler ( it's where the stainless steel 75 mm tube came from that comes in through the wall . I considered it too much hassle to mess around trying to get an adaptor made for the heater heat exchanger air inlet so did it as I've done instead . That concertina alu pipe has a hell of a surface area that will help no end in pre heating the fresh air inlet to the heat exchanger I'm sure .

 

[DickyDoDah]

The design of these heaters is that the combustion inlet takes fresh air from outside the "vehicle" so as to avoid any combustion fumes entering the occupied space in the event of a fault or backfire. Your setup is correct as far as that goes however if you can keep the air inlet as far away from the exhaust as possible it will ensure that the fuel air mixture is correct. If the exhaust accidently fed back into the inlet due to a breeze etc. there would be less oxygen for combustion and the efficiency will go down. probably not a big issue in this setup but worth noting for other installs.

The space heating is setup incorrectly as the heat exchanger totally isolates the combustion and the space heating. The combustion takes place inside a cast aluminium heat exchanger and the room air is passed over this finned block of aluminium. The maximum temperature of this is below 200 degrees C and more likely only 150 degrees C. You are concerned that this may be a potential ignition source if the internal room air is passed over the heat exchanger which is a healthy attitude to take. However the ignition temperature of petrol, for instance is 220C and cellulose thinners is 475C so not as big a risk as you may imagine.

As you have chosen to take cold fresh air from outside to feed the space heating it will take considerably more power (fuel) to heat the room as the temperature difference will be high to start with and will increase as the room warms. In fact the heater will end up burning fuel for no purpose. In a small space this will be negligible as the thermostat in the controller will ramp down the output. There is however another aspect that you may have missed. As you are pumping air into the space from outside to feed the space heater you must have a vent out of the space to release the same amount of air. This means having a 75mm hole in the wall to allow the heated air out so as to not restrict the airflow over the heat exchanger. This vent should be as low down the wall as possible so that the coldest air in the room is vented first. For this example I have assumed that the doors and windows are well sealed but in reality there may be plenty of natural ventilation to preclude the need for a vent to outside.

I'll get of my lectern now and say its up to the installer to decide what is and isn't safe and it's up to physics to tell you what is and isn't efficient
On my install I've mounted my heater up near the ceiling with an extended vent pointed down which is possibly the worst way to install it but I had no floor space where I could fit it so it is what it is. I have also extended the exhaust along the internal wall and fitted radiator plates on it to gain as much heat output that I can. I used 22mm copper pipe which amazingly was the cheapest way to do it and was a great fit onto the existing exhaust. The radiator plates are some Alu plate attached with 22mm copper pipe clips and it's all painted VHT matt black. It is surprisingly efficient and I can see 180 C at the exhaust reducing down to 40 C where it goes through the wall. It's less than 3m and a straight pipe so does not restrict the exhaust. Because of the length I don't need the silencer (they don't do much anyway) but if I did I would put it at the far end outside the workshop which is 54 square metres BTW.

 

[fizzy]

The design of these heaters is that the combustion inlet takes fresh air from outside the "vehicle" so as to avoid any combustion fumes entering the occupied space in the event of a fault or backfire. Your setup is correct as far as that goes however if you can keep the air inlet as far away from the exhaust as possible it will ensure that the fuel air mixture is correct. If the exhaust accidently fed back into the inlet due to a breeze etc. there would be less oxygen for combustion and the efficiency will go down. probably not a big issue in this setup but worth noting for other installs.

The space heating is setup incorrectly as the heat exchanger totally isolates the combustion and the space heating. The combustion takes place inside a cast aluminium heat exchanger and the room air is passed over this finned block of aluminium. The maximum temperature of this is below 200 degrees C and more likely only 150 degrees C. You are concerned that this may be a potential ignition source if the internal room air is passed over the heat exchanger which is a healthy attitude to take. However the ignition temperature of petrol, for instance is 220C and cellulose thinners is 475C so not as big a risk as you may imagine.

As you have chosen to take cold fresh air from outside to feed the space heating it will take considerably more power (fuel) to heat the room as the temperature difference will be high to start with and will increase as the room warms. In fact the heater will end up burning fuel for no purpose. In a small space this will be negligible as the thermostat in the controller will ramp down the output. There is however another aspect that you may have missed. As you are pumping air into the space from outside to feed the space heater you must have a vent out of the space to release the same amount of air. This means having a 75mm hole in the wall to allow the heated air out so as to not restrict the airflow over the heat exchanger. This vent should be as low down the wall as possible so that the coldest air in the room is vented first. For this example I have assumed that the doors and windows are well sealed but in reality there may be plenty of natural ventilation to preclude the need for a vent to outside.

I'll get of my lectern now and say its up to the installer to decide what is and isn't safe and it's up to physics to tell you what is and isn't efficient
On my install I've mounted my heater up near the ceiling with an extended vent pointed down which is possibly the worst way to install it but I had no floor space where I could fit it so it is what it is. I have also extended the exhaust along the internal wall and fitted radiator plates on it to gain as much heat output that I can. I used 22mm copper pipe which amazingly was the cheapest way to do it and was a great fit onto the existing exhaust. The radiator plates are some Alu plate attached with 22mm copper pipe clips and it's all painted VHT matt black. It is surprisingly efficient and I can see 180 C at the exhaust reducing down to 40 C where it goes through the wall. It's less than 3m and a straight pipe so does not restrict the exhaust. Because of the length I don't need the silencer (they don't do much anyway) but if I did I would put it at the far end outside the workshop which is 54 square metres BTW.

One of my heaters recirculates the hot air. The 2nd heater sucks in cold air as I couldn't be bothered to drill a big hole in the wall for the ducting. TBH it seems to make very little difference although I am sure it must. Air at 20C needs much less warming than air at 4C.
My biggest concern with not recirculating the air is the increased chance of sucking in exhaust fumes. On mine I have a long vertical exhaust stack but a bad joint could allow it to happen. Hence always having CO detectors in the rooms.

 

[Onoff]

Got one in the motor home its fantastic, Facebook has a couple of good Chinese diesel heater groups which can be very helpful

I thought China had banned Facebook?

 

[winchman]

I thought China had banned Facebook?

The groups are ran by people who have bought one not the Manufacturers, but some manufacturers do some how post on them, as they used to get a percentage of returns from people who didn't have a clue how to fit them

 

[James1979]

One of my heaters recirculates the hot air. The 2nd heater sucks in cold air as I couldn't be bothered to drill a big hole in the wall for the ducting. TBH it seems to make very little difference although I am sure it must. Air at 20C needs much less warming than air at 4C.
My biggest concern with not recirculating the air is the increased chance of sucking in exhaust fumes. On mine I have a long vertical exhaust stack but a bad joint could allow it to happen. Hence always having CO detectors in the rooms.

I’ve put load of these in boats and plant and lorries over the years.

Mostly eber as that’s what people will pay when they want reliability.

If you read the eber manual, it is permissible to have combustion air drawn from the occupancy space, I will have to look but I think it’s actually recommended for efficiency in sub zero temperatures.

Obviously there’s loads of caveats of it’ll suck all the oxygen out of the cab and you will die unless you leave the window open etc etc but it does seem to make a difference in cold climates, if you believe what you read.

I tend to fit them conventionally ie combustion side all outside, heating side all inside which is fine for the uk. Not sure about the copies but it’s best to put the outlet and inlet far apart on the eber. If it sniffs exhaust gas it’ll shut down.

 

[slim_boy_fat]

if you believe what you read.

But, who does that?

 

[fizzy]

I’ve put load of these in boats and plant and lorries over the years.

Mostly eber as that’s what people will pay when they want reliability.

If you read the eber manual, it is permissible to have combustion air drawn from the occupancy space, I will have to look but I think it’s actually recommended for efficiency in sub zero temperatures.

Obviously there’s loads of caveats of it’ll suck all the oxygen out of the cab and you will die unless you leave the window open etc etc but it does seem to make a difference in cold climates, if you believe what you read.

I tend to fit them conventionally ie combustion side all outside, heating side all inside which is fine for the uk. Not sure about the copies but it’s best to put the outlet and inlet far apart on the eber. If it sniffs exhaust gas it’ll shut down.

I wasn't talking about the combustion air but the heating side. Cold combustion air makes no difference. In fact if its like an engine colder air is better.

 

[James1979]

I wasn't talking about the combustion air but the heating side. Cold combustion air makes no difference. In fact if its like an engine colder air is better.

I was agreeing with you but read it as combustion air not hearing air!

I lost track in the thread

 

[slim_boy_fat]

I lost track in the thread

Easily done

 

[not done it yet]

I have two of these recently fitted to heat my 30 sq.m garage. I find each one gives off twice as much heat as a 3kW electric heater.

That is interesting. How much fuel do each of these heaters use. To make i excess of 6kW, the fuel usage will need to be more than 0.7l/h. With 22ml pumps, that equates to almost 9Hz.

Have you checked your pump Hz? I doubt very much that it can be running that fast.

The motor speed would also have to be far in excess of its maximum setting, too.

Also, if you really need over 12kW (or even over 6kW) you need to seriously consider some draught-proofing and insulation!

Let us know your findings. Until then, I don’t believe your claim - and neither should anyone else!

 

[not done it yet]

I use one quite often. Mine is supposed to be 5kw but I highly doubt it puts out 5kw. A tank lasts all day and good for heating probably a double garage space, maybe a triple garage space. I much prefer a multi fuel stove burning coal if you want a good amount of heat but the diesel heater is less hassle.

Definitely not 5kW. Might just about Input 5kW, but a fair amount of that energy will be going out of the exhaust.

 

[not done it yet]

I’ve now got two of these heaters - bought before Trading Standards effectively closed down the importation and sale of most of these items on safety issues - until the chinese heater manufacturers (and epay sellers) much improve their safety instructions for both installation and operation.

I very recently measured the real quantity of fuel being sent to my 2kW rated heater. My measurements were carried out to a decent standard - not like how most of the you-tubers do it.

I measured it at full and minimum heat settings and one in intermediate setting. A straight line graph resulted when I plotted settings against volumes, so I am confident I can rely on my results.

Maximum fuel usage was 195ml/h and minimum was 71ml/h.

Taking the energy content of diesel to be 10.5kWh/litre, that equates to 2.05kW and 0.75kW of energy input to the heater.

Assuming 80% efficiency, those results provide real hot air outputs of just 1.6kW and 0.6kW respectively.

I cannot remember the equally reliable result I got for the larger heater at maximum output - but it was considerably shy of 0.5l/h. At a fuelling rate of 0.5l/h the warm air output would be around 4.2kW, I would suggest.

So much for those that claim huge outputs for their heaters - even as much as 8kW, by some.

 

[not done it yet]

Fuel wise about 1.2 litres on the lowest heat setting in 3.5 hrs

That is close to 3kW output. Are you sure on the fuelling rate? Seems likely to be high for the minimum setting.