Will this heater idea work

Dear all

We tend to retrench to a small room in the house during winter months and have been pondering a low cost way to warm the room effectively without having to ramp up the gas central heating system.

Confident of my genius I have been scribbling ideas down but, as ever, I don't actually know what I am doing so before getting out the welding gear and investing in a solar panel I thought I'd seek some opinion. One of you guys will have thought of this already, or will have done it or something similar. Is it worth the effort?

The idea - internet abounds with 12V 200-300W immersion heaters (for cars or caravans??) and solar panels capable of producing that sort of of output. Some of the immersion heaters look essentially like kettle elements and some are totally enclosed in stainless steel tubes but cost is typically 20 to 30 pounds.

The solar supply options seem to be about 60 to 100 pounds including some sort of supply interface gizmo but, to my understanding, while the sun shines they spit out the required 12V and 300W.

If I was to weld, say, a 2" diameter steel tube within a small-ish 8kg propane cylinder full of sand would the heater transmit enough heat to create an overnight heat source? Some comments suggest don't let the immersion touch the sand or jacket it with water. I'm clueless but was aiming for a totally dry set up.

Hoping for something more effective than tea lights under a plant pot and the steel casing could/might allow for an easy increase in surface area by addition of fins or whatever. A guy on youtube has offered a design using a sand filled pipe heated by tea lights with the fumes vented through a charcoal filled chimney. I am not massively keen but if the floor decides that is better than the solar option I could go down that route.

Intention would be a discrete solar panel in the garden and a cable to the heater. No other items to be connected bar maybe some led lighting.

Am I being stupid? Might this work? I don't need fabulous levels of efficiency and am not after 1000C and enough energy to warm Finland or wherever the big boy version is. I am really only after a basic pot belly stove effect. Would this get to, say, 50C assuming decent sunshine? Would that heat a 15ft by 10ft room?

As a minor aside I had also thought about an additional hole to receive a simple billet that would be heated whenever the oven was used and transferred. Rather like heating a brick by the fire and taking it to bed (was that only us?). That would allow some sort of occasional top up.

If the approach is nonsense feel free to say so. I can take it! No experience of solar panels. Dubious welding ability. More reasons not to try than to attempt it - I could be working on that traction engine.

Andrew

They are trying it in Finland as you suggest.

Sand is useful because it can hold heat because it doesn't transmit it.

The issues are:

1 Getting the heat in.

2 Getting the heat out.

To do this you will need to run pipe in the sand from your immersion heater to warm it.

Run another circuit in sand to extract the heat.

A couple of points...

Running immersion heaters of any kind without a water jacket is asking for trouble - they are designed on the assumption that they will be in contact with water and will potentially overheat if they are not.

Heating up a brick in your oven simply increases the amount of time it will take for the oven to heat up - there are no free lunches there I'm afraid.

If you get 300W worth of sunshine during the winter months (very far from certain I'm afraid), the best you will manage is about a couple of units (1 unit = 1 killowatt-hour) of stored heat - so equivalent to having a convector heater on for about an hour. Bear in mind that the heat will be given out over the full 24 hours. I doubt if you would see much benefit TBH.

+1 on Tony's comment on using immersion elements without water. They are designed for fast heating so need the water to control the temperature.

Another issue is that solar cells don't work well with fixed resistance loads. For your sand heaters idea you could use some MOSFETs on a heatsink in the sand and a maximum power point tracking (MPPT) controller.
BUT
You would probably be better off using the solar cells to charge a 12 or 24V battery and then running a car or truck fan heater off the batttery when you actually need heat.

Robert.

Edited By Robert Atkinson 2 on 22/09/2023 12:44:55

Short of chopping up a tree with an axe there is no way to produce free heat. What needs to be done is reduce the heat loss as much as possible therefore reducing the amount of heat input to a minimum. All heat input costs money and in the UK even wood stove installation is controlled by local councils, not sure wether it is everywhere certainly is where I live. Without spending a great deal of money there is no way to heat most UK properties cheaply. I think the number of tea candles required to heat a room would cost far in excess of your normal electric supplier.

If you considet the use of car batteries, calculate the tihe to run out of charge (battery amp-hours divided by current drawn). I ran down my car battery with one of those small 'fridge' coolers, which didn't have much current draw. A bit depressing when I went to retrieve my car later that evening, in the dark!

Bill

I wouldn't use car batteries, they don't like deep discharge, Leisure batteries are the thing. As others have said, 1 300W solar panel won't give anything like that on an overcast winter's day, and it's only daylight for around 8 hours per day in midwinter.

A data point. We have a modern large storage heater in our kitchen/diner which is heated at night probably for 4 hours from cold consuming 3kw, so total of 12kwh. That keeps background heat in the room until evening. You might use one a third the size for a small room so 4kwh. I don't think a 300w solar panel will cut it in winter daylight.

Many thanks to you for the learned insight. I'll save my money for something more sensible.

Always grateful to have access to the combined knowledge on this site...

If you look on youtube there a lot of folk who have fitted the chinese diesel heaters outside of there homes & ducted the warm air indoors with a lot of success. I fitted one to my workshop (i wont put a link to the video on utube ) But it's there. My workshop is 3M x 4M & it gets toasty warm in winter. I spent a total of £42 throughout winter on diesel. That was paying top price for fuel. I have since found the local flying club sells Kerosene much cheaper.

It is an alternative that works & a lot of forum members on this site use them i discovered.

These are what are fitted to most Campervans.

Steve.

Bear in mind that a given solar panel in December will produce roughly one sixth of the mid summer output.

By the way, an excess of solar generation sounds like an excellent way to destabilise the electricity grid, since the plan seems to be to mandate heat pumps, whose COP will be a minimum at the same time as the solar output is also a minimum.

NO NO, Hell NO!!!!!

These chinese diesel heaters are not well made, are not intended for use in dwellings and are not approved for this type of use. Most of them are not properly approved for ANY use. If it burns the house down you will probably find you insurance was invalidated by usin one.

Additionally Steve, assuming that the "kerosine" you bought at the flying club is aviation fuel, you have just admittedt to fuel duty fraud on a public forum. I can't see why you would by any other kerosine from a flying club. It is also illegal for them to sell it to you.

In contrast I buy Jet-A for my gas turbine engine from a responsible supplier and have to pay the full rate of duty. In theory as I'm using it to test an aircraft engine it should be duty free but the supplier, quite reasonably in my view, say that ANY sale that does not go into a aircraft or ground support equipment on the airfield is charged at full duty. The small number of sales is not worth the effort to ensure that it is not duty evasion given the consequences to their business if it is. If I don't like It I can go elsewhere as far as they are concerned.

Robert.

Years ago, in a TV series … Dick Strawbridge showed a thermal energy store using a pit full of crushed glass

But I think it was only supplying night-time warmth for his greenhouse

MichaelG.

If you intend on buying kerosene or red diesel, buy it from a petrol station that sells it. You do have to fill in a form. Using it for heating is a permitted use. (For either red diesel or kerosene). About 80-90p a litre.

Oh Dear.

I tried that last year. Red diesel is what I was using. It was not much cheaper. From the higher up posting it seems the flying club may not let me have any. There is a place at Brighouse not too far from me that does sell Kerosene in small amounts . Most want you to buy 400 litres at a time. I should only need around 50 Litres for the winter.

Steve.

Correct. The problem with Aviation fuel is that it is not marked (dyed) so they can't easilly tell if it is used in a road vehicle (highest taxation class). This means there are stricter regulations and controls on it.
The reason it is unmarked is because the marker could interfere with correct operation of the aircraft systems. Even if it didn't the specifications for the fuel do not allow the addition of markers.

The laws were changed fairly recently with more restrictions on reduced duty fuel. You can no longer use it in transport refrigeration units and pleasure boats can only claim a rebate for the portion of fuel used for heating rather than propulsion.

Robert.

Steviegtr, I live in a semi rural area where we have petrol stations which serve the farming community and have pumps for red diesel and kerosene. You know have to fill in a form first giving your address and what you are going to use it for.

Kerosene isn't marked. It also looks like and smells a lot like diesel. (It will ruin a diesel pump and injectors if you use it for such though).

Last winter I rang all the local to me stations & none sold Kero. Some had done but no longer did. I will try a few more just to see.. Thanks for the info though.

Steve.