Concept elec cabin heater - small draw

[TassieTiger]

So, wanting to develop and mess about with heating a tiny house style cabin using solar / battery and if you look around, there is nothing available - it’s either gas, wood fire, 240v or massive DC draw only.
So to answer the why not questions-
Gas - don’t want to drag bottles and kids will stay here next winter.
240v - not available in middle of no where.
Wood - yes. Did wrestle with this but tiny house means small areas, hard to get a wood heater burn over night without over whelming the place to start with, and again - kids...monoxide poisoning without vents...etc.
Huge fire pit outside...regardless.

So, a few ppl offered ideas last time that I floated this and well...here I am...at this point.
5 x 28w (12v) thermistors resting on a water filled radiator with a PC mini fan circulating air from underneath.
This device when vertical, raised room temp by 7-8 degrees in an hour - but I then turned it off as worried re temp of thermistors. I need to cool them better. They were at 184 degs!!!
Note - 1 of these thermistors boiled a cup of water in 30 minutes...sounds terrible until you understand the tiny power consumed to do so. 1.2 amps to boil cup water. (Perspective = you could theoretically boil 12-16 cups of water with a single charged D cell battery!)

The thermistors total 150w (5x30w) per hour at 12v = 12.5 amps per hour.
8 hours heating for 100 amps for heat.

So now to look for efficiency - the thermistors are generating almost 200 degs C. They really need to be incorporated into the fluid somehow - ? Open one side of radiator tank maybe? The pc mini fan may need upgrading to move more air - or a second unit added. Water vs vegetable oil - not sure what would work best?
And I’m not sure if thermal dynamics will get fluid moving within the radiator or whether one end is always going to be colder...
Thoughts or ideas are welcome.

[Die Judicii]

Couldn't (resist) get the play on words ?

Well Tassie,, seeing as your waaaaay down south,,,, why not go for your very own mini nuclear reactor ??

[TassieTiger]

Do you know how many smoke detectors I’d need to get ?

[Blr243]

There are people on YouTube who have made their own helicopters ( and from the clips I have seen I think they are still alive too) I wonder if anyone has ever attempted to make a mini nuclear reactor on the sly ? Anyone in your street seem to be having a lot of concrete trucks lately?

[eddievic]

BLR Lisa Simpson, and young Sheldon have tried.... with not good results. In young Sheldon case people in hazmat/nuclear suits visited his house. Idd he worried about you being labled a terrorist.


Actually glad you have come back to batteries and theses little heaters. Thinking about it a few thoughts come to mind.

Playing with 12v is very dangerous esp when you start going high amperage. A short circuit can result in fire and can burn the house down. I am sure you know, but for others who might be playing at home.

What are theses thermistors rated to run at temp and time wise. Have a look at their specifications sheet. I would think about using a copper heatsink maybe even like a cpu one with a high flow fan. Or just have a blower fan. The idea being air is taking away the heat as quickly as possible.

Put the whole setup on a thermostat with a timer. So say it runs for 20 minutes then off for 5 minutes, instead of running for 60 minutes. But you may find that theses prefer running instead the stresses of too many cooling and heating events

For your liquid component Have a search on what they use in hydronic heating systems, or radiator systems in europe.... its it just water or has some rust inhibiting and anti boiling additives.

[TassieTiger]

I believe a ptc thermistor is not necessarily utilised as a heating device perse - they actually increase in resistance when heated...they are designed (I believe) to stay on rather than on / off. But I have bought a temp control switch in case too hot...

200 degs is farrrkin hot - like INSTANT burn hot, so they are going to have to be at least semi submerged...

I’m starting to think the radiator was a waste - I should have just bought a metal bowl, filled with water, dipped the 5 x thermistors into the water, had a fan blowing across top. Boiling water would not happen if I kept at least 15 litres in there...

[eddievic]

Having water will increase humidity mate.... long term you don't want that.

What i was thinking was like those diesel burner heaters, they are the long cylindrical type, but instead of burning fuel you use your thermistors to generate heat. The air flow will be enough, and they week not be easily accessible by children

[Ziege]

I would just run a fire outside and heatpipe in from there,

[TassieTiger]

Having water will increase humidity mate.... long term you don't want that.

What i was thinking was like those diesel burner heaters, they are the long cylindrical type, but instead of burning fuel you use your thermistors to generate heat. The air flow will be enough, and they week not be easily accessible by children

Yeah - condensation would suck...that’s one reason I thought oil...but a potential oil fire is a farkin nightmare.
A guy on utube placed the thermistors between a couple of big bricks and the stone held the heat for dispersion...very simple and it worked...could store it easily as well.
I get what your saying with diesel heaters - old msn has one in his van...it’s not a bad idea. A cylinder with a same diameter fan to move the air - would be easy to mount the thermos as well...but - I’m still worried about these things potentially over heating - they probably wouldn’t...maybe that’s my next test - I bought 10 to kill off 5 ($2.90 each) in testing...it’s hard to believe how hot they get.

In fact, I bought a 12v kettle a while ago and smashed it in a fit of rage as 30 mins and water was at about 40 degrees...these 2,90 things would be 20 times more efficient.

[TassieTiger]

I would just run a fire outside and heatpipe in from there,

Contemplated this and did try, but cabin is built on a rock bed...and crow bar beat me. Cant get mini digger in any more. And the solar gear I got was very very cheap.

[Ziege]

is the wall built out of rock bed?
why bother trying to come through the floor?
just get a regular 2nd hand tile fire, put it on the outside wall, so as to have a long burning fire, pipe heat in through the wall... done.

[TassieTiger]

is the wall built out of rock bed?
why bother trying to come through the floor?
just get a regular 2nd hand tile fire, put it on the outside wall, so as to have a long burning fire, pipe heat in through the wall... done.

Would have to go UG because of pathways between cabin and fire place, ppl would tripping over rigid pipe - there are 3 tine points thst could be used to get into floor but it’s the whole retrospective build - undoing crap to retro fit stuff is twice as difficult.

Also considered this backing a tile heater onto an external wall - it’s shipping container steel which would conduct well, then Bradford insulation and then pine studs and VJ pine lining. But it’s still an external “fire” with kids...

I’m confident the elec will work, just needs some smarter ppl to kick some things around...and if it does end up coming off - then, I’m sure someone, somewhere, will also benefit from following the “concept”.

I think I’m going to leave a thermistor on for couple hours and just see what happens...I’ll do it away from house / shed...if it burns out or sparks - they will be history!

[Ziege]

I think you have too much time on your hands and are overcomplicating things, take some pics of the area, I am not convinced this is as difficult to work out as youre making it seem.

[TassieTiger]

I think you have too much time on your hands and are overcomplicating things, take some pics of the area, I am not convinced this is as difficult to work out as youre making it seem.

It’s not difficult to be conventional.
I want to make use of the solar equipment that I got for almost nothing - a 300w panel, 520ah battery, 30amp regulator and if required - a 1500w/2500w inverter. I did some work for someone and that was payment.

[Ziege]

Electric space heating is notoriously inefficient, this is why using electricity to operate a pump (reverse cycle air-conditioning) is the status quo. hence there are very little to no battery/solar heating solutions, air as a general rule has a high specific heat capacity, and therefore has a greater latent heat capacity, meaning the energy absorbed by it and re-emitted is done at a high rate plus it takes a lot of energy to heat that air before any noticeable change in endothermic emissions from said air takes place, hence why bayonet heaters and coil heaters, and electric oil heaters are usually very inefficient, LPG or Natural Gas heaters are cost effective also but very inefficient as are wood fires. inefficiency based on the fuel in heat out ratio. wood is the cheapest to run, so for Joule to Dollar ratio would be at its best using a log burner in some capacity.

If you are hell bent on using electricity do what everyone else with the knowledge and science and experience has done and stick with phase change gasses aka buy a small aircon.

I can relate to where you're at, I was there a while ago, experimented with a great many concepts, I have a whole file here on solar/storage/heating/cooling solutions, all of them were either tried or hashed out by me and the guy that used to be my tutor in high school and college (a chemical and mechanical engineer that works for Boeing). If I find it in the attic I will take some pics and upload them.

I had a similar concept a while back when I had my son staying in the outside bedroom in the old farm house (while building our new place that is designed by me and needs 0 air conditioner or heater and it gets to -8*c here in winter and 40*c in summer) The solution ended up being an old tile fire setup outside, the water heating element that was made to attach to the Flu on the chimney was close looped onto an old copper that I bronzed a lid onto with a pressure release valve off an old air compressor put on it. the loop consisted of going through the wall and basically was a 1' long windy panel of copper pipe exposed as a "heater" in the room, and I simply insulated the rest of it including the copper with anticon insulation. 0 risk of "smoke" or "co2/co poisoning, and one log on the fire with coals and its good to slowly burn all night. easy peasy.

[TassieTiger]

Electric space heating is notoriously inefficient, this is why using electricity to operate a pump (reverse cycle air-conditioning) is the status quo. hence there are very little to no battery/solar heating solutions, air as a general rule has a high specific heat capacity, and therefore has a greater latent heat capacity, meaning the energy absorbed by it and re-emitted is done at a high rate plus it takes a lot of energy to heat that air before any noticeable change in endothermic emissions from said air takes place, hence why bayonet heaters and coil heaters, and electric oil heaters are usually very inefficient, LPG or Natural Gas heaters are cost effective also but very inefficient as are wood fires. inefficiency based on the fuel in heat out ratio. wood is the cheapest to run, so for Joule to Dollar ratio would be at its best using a log burner in some capacity.

If you are hell bent on using electricity do what everyone else with the knowledge and science and experience has done and stick with phase change gasses aka buy a small aircon.

I can relate to where you're at, I was there a while ago, experimented with a great many concepts, I have a whole file here on solar/storage/heating/cooling solutions, all of them were either tried or hashed out by me and the guy that used to be my tutor in high school and college (a chemical and mechanical engineer that works for Boeing). If I find it in the attic I will take some pics and upload them.

I had a similar concept a while back when I had my son staying in the outside bedroom in the old farm house (while building our new place that is designed by me and needs 0 air conditioner or heater and it gets to -8*c here in winter and 40*c in summer) The solution ended up being an old tile fire setup outside, the water heating element that was made to attach to the Flu on the chimney was close looped onto an old copper that I bronzed a lid onto with a pressure release valve off an old air compressor put on it. the loop consisted of going through the wall and basically was a 1' long windy panel of copper pipe exposed as a "heater" in the room, and I simply insulated the rest of it including the copper with anticon insulation. 0 risk of "smoke" or "co2/co poisoning, and one log on the fire with coals and its good to slowly burn all night. easy peasy.

Agreed - the low draw elec heater doesn’t really exist. It may well turn out not to be viable - but, thus far, it is promising.
I don’t know how old the idea of PTC thermistors is ? if it weren’t for them, then I’d not even attempt this - but they are, pretty darn efficient as already mentioned. 28w for 200degs c...I’m absolutely mind blown how hot they can get from so little power, it’s really quite amazing - but - how long will they last at 200 degs? Being a ceramic resistor, I’d assume a decent time but I know very little about these...

I like the copper pipe heater idea - I could actually twist this and do similar, using the thermistors in place of heating element - similar to Eddies idea. How did you regulate the water element and I assume it was mains ?

I don’t sleep all that well (never have) and end up just thinking about different problems and potentials and all manner of wild ideas and s**t all bloody night...this is but one that grew some legs lol.
Ps Eddie - I researched re turning thermistors on/off and apparently, that will kill them / they have a finite no of cycles available per unit. So with that in mind - 2 options. Try and burn one out on purpose to understand life of, or semi submerge the units constantly to control the heat.

[TassieTiger]

This is from one of the security cams showing fire pit area and front of cabin with toilet in distance.

[Oldbloke]

Old nursing homes and hospitals used to do it by having a boiler in the basement and then steam or hot water was then piped to a type of radiator (usually cast iron if I remember correctly) in the room no fans required.

Although old and simple these systems were fairly efficient.

I'm also scratching my head over why not a flued pot belly?

[Ziege]

water is solid unit, the coil for the heating was placed the same height as the bottom of the copper that was feeding it, this way air was kept to the copper and convection took care of the rest, in any case the entire system was always hot enough to heat the room. sealed unit so no there was no mains... steam vented off through the relief valve...

[Ziege]

as for the carbon monoxide, there are acres of cabins in the Canadian wilderness sealed up to stop draughty air from making them cold with open fire places, a pot belly or tile fire with a flue is never going to be a problem. unless installed incorrectly.

[trekin]

is the wall built out of rock bed?
why bother trying to come through the floor?
just get a regular 2nd hand tile fire, put it on the outside wall, so as to have a long burning fire, pipe heat in through the wall... done.

Would have to go UG because of pathways between cabin and fire place, ppl would tripping over rigid pipe - there are 3 tine points thst could be used to get into floor but it’s the whole retrospective build - undoing crap to retro fit stuff is twice as difficult.

Also considered this backing a tile heater onto an external wall - it’s shipping container steel which would conduct well, then Bradford insulation and then pine studs and VJ pine lining. But it’s still an external “fire” with kids...

I’m confident the elec will work, just needs some smarter ppl to kick some things around...and if it does end up coming off - then, I’m sure someone, somewhere, will also benefit from following the “concept”.

I think I’m going to leave a thermistor on for couple hours and just see what happens...I’ll do it away from house / shed...if it burns out or sparks - they will be history!

If your PTC's are not the silicone type, then they are self regulating, they'll heat to a pre-determined resistance then shut off until they reach a second pre-determined resistand value, where they'll fire back up.
I'd still go with the concrete block, but cast my own with the thermisters inbedded (the more inbedded the betterer) in them. Then build one of those stove top fans using Peltier as the power source for the fan motor; https://www.youtube.com/watch?v=ML0JQENP6IQ Just don't cast the block so big as to not be able to easily move it around so that you can place it outside in the sun, or next to the fire firepit when you first arrive up at the cabin, this way you are using an alternative free source to bring the block up to temp from cold, thus saving on your batteries.

[Oldbloke]

as for the carbon monoxide, there are acres of cabins in the Canadian wilderness sealed up to stop draughty air from making them cold with open fire places, a pot belly or tile fire with a flue is never going to be a problem. unless installed incorrectly.

100% correct. if you're worried just install 2 vents1 each end of the cabin like this caravan vent. This is plastic, but there are steel versions

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