Author Topic: House heater.  (Read 6811 times)


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House heater.
« on: September 29, 2022, 07:18:52 pm »
With my old Ducted AC struggling to heat the house in winter and using a lot of power not to do it, Decided to build another heater for the house.
Being this was DIY and well into the winter time I got round to it, I didn't have time to set up safety features and I wanted it to be safe  and Potentially disaster Free.

For this reason I decided to use water as the main heat transfer medium  rather than direct air I was going to initially use air but as this would give a direct path for a run away fire to get into the house, I decided to put that idea aside till I thought things though better.
I ended up with 2 Versions of the burner for the heater.
  The first was a submerged Burner.   Got a piece of 150mm pipe, welded one end shut and got a bit of 50mm for the air tube and bit a bit of 6MM copper down the middle for fuel feed.  I wanted maximum heat transfer area of the pipe to the water and my  aim was for a max 10 Kw heat output.

I drilled some holes in the down tube and welded on some Tabs to hold the flame and  make it turbulent so there would be more contact with the hot gasses and the main burn tube.  This is important to break up boundary layer gasses as otherwise the outer coloumn of air gives up it's heat to the pipe which is transferred to the water but the inner gasses go straight up and out ( or along if horizontal) and don't give up their energy when is then vented and wasted.

Because HEAT is the key to oil burning of this type of combustor and The main burn tube would be water cooled in effect, I made a small insert  piece for the air fuel tube to sit in which would get red hot to burn off the carbon and act like a big glow plug.  In testing the burner in free air, the family ended up coming out and sitting around the thing where I had set it up and was doing a test burn one night and the only complaint was we were all backed up against the walls of the covered verandah and too hot even when the thing was running pretty low.

  I thought this would be excellent for keeping frosts away in the garden with a fan blowing across or a great shed heater if a flue was put in the top if it were a small space  without a high roof. That said, Checking with my CO meter, the thing runs clean enough to come in under the 8 hour exposure level of breathing the gasses so really not that much of a concern if it wasn't flued in a reasonable are where the gasses could escape and there was some ventilation. The radiant effect would be perfect  in that scenario.

I put a small Bilge blower on the down tube for air supply and ran the oil line down the middle to the bottom so the oil would be blown out half way down the tube or carbonise in the air tube and block it.
Sank it all into a drum of water and sat it on some bricks so it wouldn't melt the plastic drum I was using for testing.  And NO, It didn't melt as can be seen in the pics and I boiled the hell out of the water which was hot as it would ever get.

For fuel control I used a cheap Fleabay Fuel pump and controlled that with an interval timer.  This is really a key part because although so many go on about the simplicity of a drip feed, it is totally useless for unattended running as I wanted this thing to be.  I wanted set and forget and with a measured and constant fuel delivery, that's what I got.  The only variation was the cold could make the oil thicker and it would slow down but that was acceptable as long as it did not run away. I did have a PWM controller on the blower but that turned out not to be needed and more complication so I ran the fan flat out and to slow it down for lighting or  low power running I used a bit of cardboard across the inlet and that worked perfect.  In normal operation it runs wide open and creates an oxygen rich fire which makes it burn so clean.

To get the heat into the house, I ended up with an intercooler from a car and put a circulation pump on that. I made up a wooden box as a plenum and put a tube fan on it to suck air through and duct it through a window.  This worked but was mostly wrong but was a matter of the materials I had on hand and could put together in a day as it turned out.

Firstly, the Pump should pull from the resivour and push through the Radiator ( intercooler in this case)  so any air is expelled.  Drawing through although meant the pump  got the coldest  water ( and the pump is rated above boiling) but was also difficult to get the air out the system.  Next time I'll draw from the tank and push through the radiator.

Other mistake was to use an Intercooler.  They do not draw enough heat out and the  cross flow  sections ( whatever they are called) are too widely spaced and too thick with not enough fins to extract all the heat.  It worked but the water temp coming out the thing was too high and there was not enough drop.  Didn't really matter because little heat was lost as it returned to the " Boiler"  but annoyed me as an inefficiency. I later remembered from my go fast days that intercoolers of this type are mainly dependent on their mass to cool the incoming charge air as  few turblow cars are on full boost for more than 10 Sec at a time.
I tried a car heater core initially and that was great but the one I had was small and the limitation was the low pressure fan. Cars usually have blowers which do higher static pressure and get the volume through the core.

I have researched online and found that there are car heater cores available in the US that are a universal fit and sold for hotrods etc. They have the core, blower and a speed control all in a nice housing. The largest I found did 12  or 15KW, for get now, but perfect for what I wanted and there were smaller sizes as well.  They weren't cheap in our money but typically shipping anything here from the US is total and utter bullshit in how expensive it is, So they were not Viable.  Haven't found anyone that has the larger ones here.  With free shipping in the US, These would be perfect.  Sit the unit in a window, connect up the hoses, a 12V power supply and done and they look decent as well.

The reason I went to the complication of using water as the working HE medium was because again of safety.  No way for any fire to get to the house as the burner is situated well away ( slim risk of fire as it is) and the Inter cooler was also outside so if there was a leak, I have 200+L of water on the verandah outside where it don't matter rather than creating a no contest Divorce case if it flooded the house inside.  Doing it this way simply avoided as many risks as I could forsee.

So did it all work?
And No.

The weak link was the Intercooler and fan.  That side could not keep up with the output of the burner.  A car or bike radiator would have done the job MUCH better. I have since modified a car radiator and electric fans which will well and truly over cool the incoming water  and I can use a PWM controller to get the heat output perfect.
That said, although took a few hours, I could heat my large house to the point of well being too hot.  I would fire the burner up about 3 PM and  it would keep the house nice till I shut it down about 9 am the next morning. The thing I was not happy with was the heat up wime mainly.  I wanted to be able to blow 10 KW into the house and have it hot in 30 Min or less and I think with the right radiator and fan Combo, that's easily Possible.

I made a lot of modifications to the burner tube which were adding a lot more air holes and tabs along the length to swirl the gasses and flame front  and also keep the burner insert hot so it burned off all the carbon from the oil.  The burner tube would stay nice and clean  as well showing complete combustion  and of course the thing had ZERO smoke.

The biggest mistake with the whole thing and I still can't fathom how I did it as I still believe my numbers should have been right, is to Miscalculate the heat  required.  I designed for a max of 10 KW output and that wasn't enough really.  The heat up was too slow for what I wanted and I'd have to run the thing flat out on the coldest days for a few hours which indicated my calcs were off. Once up to heat, the thing could be turned down but getting it there was too slow for my liking.  I compensated that by starting earlier as here it usually warm enough when the sun is out not to need heating till the afternoon.

Despite being designed for 10 KW, run flat out the burner would do just under 30 Kw by my calculations.  The problem there was the efficiency I so carefully calculated with the diameter of the tube with gas flow speeds and surface area went right out the bloody window.  As much heat was being blown straight out as was being put to work and free fuel or not, that drove me nuts!
Sure, It will do 30 KW OK but I'm using about 60 Kw worth of oil consumption.  Yeah, it's free oil and I have an unlimited supply thanks to a friend but that really Irked my sense of Efficiency OCD. Any idiot can make a big fire, putting the energy to useful work is whole other skill.

At 10 Kwh the thing is great and the efficiency is good but that just wasn't enough for my house in the coldest times which get just below zero.
For what I designed it to do, and I still think that numbers are right and can't work out where I am going wrong, it's not the transfer though the IC,  it's good but like anything pushed beyond design limits, it falls over on efficiency about about 15 Kw output.

Now I know, the one thing most people reading are looking for is  " How much oil it use an hour?"  which is to me sorry,  an annoying question because it is totally Irrelevant.

I could dial this thing down to about 300Ml an hour. Way below what I thought it would sustain but it did. That's roughly 3 KW. Flat out it can go through about 6 litres an hour but that's like " emergency power" and is very inefficiency for the heat delivered where you want it.
Fuel consumption is irrelevant because I can easy dial it down to 1L an hour but if that's not enough heat output and my house is still cold, which defeats the purpose of the whole exercise!  May as well put a little 1KW bar radiator in the middle of the place and say " Look, only uses 1KW" ignoring the fact it's basically useless because the heat loss in the place is greater than that.

Work out how much output YOU need for YOUR situation and design for that.... Only do it a lot better than I did. The amount of oil it needs is what it needs. If you don't have terrible inefficiency, who cares what the consumption is?  the goal is to keep warm and comfortable not save free waste oil!

Now all that said, I was going through about 20 to 25L of oil a day depending mostly on the weather.  I did burn Both kinds of oil, Veg and Diesel engine oil. I HATE engine oil. filthy stinking staining black Shit.... but that said I have an endless supply. I still found the Veg to be better. Burned cleaner with less deposits and took a bit of tuning to get the burner to run clean on engine oil when it was perfect on veg.
Veg smells a lot better although that said, once the engine oil is dialed in right it's OK but if it's at all off, it stinks even if there is no viable smoke. We are coming into summer here so I hope to be able to collect and put away at least 2000L of veg and I'd much prefer to get 4000L  really. I think our power system is going to be in trouble and I want to be able to fuel the diesel Generators I have Built of veg over WMO as I'm far more familiar with veg and how it burns in engines.

For a lot of houses especially those better insulated than my Glass house, this would be more than enough at 10 KW output.  Turning it down is efficient, turning it above the design parameter is not. Running right I was getting an output air temp of about 50-60o C constant running which was OK.  With a better heat exchange instead of the intercooler, I'd probably get it more where I'd like it at 80 or so.  I could get that  when the tank was at heat and the fan turned down.
Anything below 30  feels cold and that's the Min temp output in Air conditioning.

The thing does have a Noticeable rumble that the neighbors Heard when they come out to their back yard but they thought is was the sewer Pump out running or a tap going. I asked if it was annoying and they said they couldn't hear it at all in the House and were only concerned that something was wrong.  I can hear it in the house very clearly but I find it very soothing.  It did flame out once because the hose came out the fuel drum and I could hear the change in tone and knew something was wrong. i  went out and found the simple problem and the thing stuttered for a bit then  kept on going as normal.
At night iT seems to put us all to sleep so certainly no problem with the noise of the burner. More an asset than anything. The fan we simply can't hear being outside and very quiet anyway.  Cats soon found a chair near the window that caught some of the warm air coming out and would sleep there all the time.

I will add a Thermostat to the setup because when the thing is switched off, there is still over 10KWh of heat in the water drum which I ended up Insulating which was an improvement. This way when I shut down the burner, the pump and fan will keep running till the water gets cold and then shut off.
That said, Shutting off hot wasn't a bad thing. Meant there was heat there ready to go when I fired it back up.

I ended up doing a MK II version  that kicked out way more heat ( up to 100Kw!!) and runs beautifully efficient so if there is any interest in that and people are still awake after reading all this, I can do a write up on that setup.

« Last Edit: September 29, 2022, 07:21:01 pm by Oilburner »


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Re: House heater.
« Reply #1 on: September 29, 2022, 09:16:01 pm »
Wow, excellent write up, good job!  Yes it was long, but it was all interesting information and I read the whole thing  :D.  That is an interesting setup, so you are actually burning the fire inside the water to heat the water?  I guess just another way to build a boiler.  I do like the idea of having the fire outside of the house and use water to transfer the heat.  I did similar, but converted a home heating oil boiler and have it in the garage with with water pipes going into the house.  Heat is transferred using a plenum insert (basically a big radiator) and built a box similar to yours and used a squirrel cage fan from an old furnace to blow heat into the propane furnace ducts.  Thanks for taking the time to share and post pictures.  Awesome project.  And love the efficiency OCD too.  I get it, why burn to heat up the outside air... not really the point.  Get those BTU's inside, or Kw's as you refer to them  ;).  And I fully agree, the black diesel oil is the worse... black stuff will stain things up in a hurry.  I am always pleased when I get friends gasoline engine oil.  Its still sometimes brown and has a slight sweet smell of gas.

Thanks again and safe burning!


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Re: House heater.
« Reply #2 on: September 30, 2022, 08:44:37 am »

I am no good at writing short because if you do, you only have to go back and answer questions about details you left out.  Often more than once.

I guess you could say the setup is like a single Tube boiler.  That's a perceptive description.
I haven't seen anyone do it that way before.  Normally it's something else that send my OCD into overdrive, wrapping copper coils around something.  WTF is it with everyone  using copper coils for any heating purpose?

In actual fact the surface area for heat transfer is quite low especially when one half of the tube is not exposed to the heat and  radiating to the atmosphere. Apart from that the contact area with something like another tube is tiny and little of the available heat is transferred.  That's why I sank the tube, to get the max transfer area and plenty of it.  There is a LOT of copper transfer area in that tube, more than double it's length to get near having the same effectiveness.  I did think about putting a copper tube inside the burn tube but that would likely just turn the water to steam which was the last thing I wanted in that setup.

I did also think of pushing steam through the HE but steam is wicked stuff even when it is only technically water vapor and is hard on any Non metal fittings, even silicone tubing.  Would be OK if I could do it all in solid metal and compressing fittings but seeing I can't, I took the safer option.

In all that I forgot to mention that I did change to a metal Drum and I insulated it with common house hold roll insulation.
I was amazed at the difference that made. I didn't even insulate the bottom of the drum and still the water would be quite hot for 2 days after the burner was switched off. That I was not expecting.

It does give me thought for a different setup where I use an IBC as the water storage and insulate than and then do a hard burn and store the energy in the IBC. That would give me about 66 KWH of useful heat energy and would make the temp easy to control during the night as the fan on the HE to the house could be put on a thermostat and just push air as required.

The mark II version uses a commercial heat exchanger from an old pool heater and works on the hot gasses more than flame impingement.
It proved to be more efficient than the tube burner at higher output rates but that's driving the submerged burner beyond what I calculated. I could have put the preheated water through the HE in the path of the exhaust gasses which would have been efficent but that would be difficult to Set up.  I am thinking of trying to double stack the HE's as I have another one and that would pretty much pull all the energy out bar the temp of the water itself.

I'm not 100% happy with the burner for the HE Core and will try and develop another one over the summer. That's hard trying to work on heating burners when it's 40 O C here. Was the reason I left this so late to start in the first place among other things. It's just burning the oil clean with a little build up over 40 Hours which is the max I have run the thing non stop.  I now have the heat absorption capacity in the heater core over the fire  and I'll certainly have it when I change the intercooler to a car radiator with at least 150KW cooling capacity But I don't have the output in this burner.  I think I'll go back to a swirl design that is squat and fat and has the discharge outlet  sunk into the burn chamber so the flame does not blow out easy and there is plenty of retained heat in it. 

Funny, I haven't burnt much petrol engine oil and sort of forgot the difference. All I have ever seemed to get over the years is Diesel oil and what I mainly had myself as I also have run my vehicles until recently all on used Veg oil.  Old diesels are getting hard to find here and the Mrs and daughter wanted to update so have gone to petrol unfortunately.
I must get some of that oil and try it.

I'd really like to try ATF in the burner.  I have been going to test it for years with the tablespoon/ blowtorch test to see how much residue it leaves. I have a feeling it will be little which would make it a good fuel. It may also be thin enough to put through a pump and spray with fuel injectors which would be ideal as the pulse rate could be easily controlled and deliver a very precise output that would be easy to get complete combustion with.

Be keen to see if anyone else has done a house heating system like this and what their approach was.