Designing an open cooking hearth and chimney for a tiny house on a trailer?

Hi all.  I've been kicking around the idea of a simple tiny house on a trailer for a while now. I've lived in a number little cabins, boats and tents over the years, and I think I'd like to have something like Thoreau's cabin in my life.
 There are some zoning issues that  a registered trailer  simplifies, and perhaps some day I might want to move from the backyard to  a spot next to a pond.  

I haven't done any engineering, but I assume that an open plan 8x16 cabin with an 8x4 covered porch and no systems would be pretty light except for the open cooking hearth that I realy want.

What I'm thinking about is is a welded up hearth and firebox and chimney for that mater.  I think some of Benjamin Franklins earliest  inserts where still designed to cook with, but I want a pot crane and  a big enough hearth to cook a meal.   I also want to be able easily install a small air tight stove if heating becomes a priority.

One of the big questions I have is whether there is any kind of light weight fire proof material that I can use as a loose fill behind the fire box and around the chimney for insulation and a bit more thermal mass? another is more cosmetic, but I'm wondering if I can do some sort of tile work attached to the steel fire place that would maybe survive transport?

Here's a couple pictures of  other reconstructions of Thoreau's cabin:

I dont see any problems.
Instead of an open fireplace, a small rocket stove for cooking maywork with a flat plate for cooking.
Even a crane swung over the same burn spot could work.
Small yatch heaters are available which will do the heating very efficiently.
If you build a steel insert with the heat blanket material where needed, that can be installed at one end of the tiny home, I believe it would work very well.
Or look at a cast iron unit and a steel plated insulated area in the cabin.

We built a chicken house (50,000 birds) and it was suggested we use "sawdust concrete" to lighten the floors weight. Basically, it used sawdust instead of sand and rock to make it lighter. It held up for 30 years of tractor scraping, but there was not fire on it either.

I do not see a true masonry stove working in a mobile capacity. It is not just the weight of it that would make it prohibitive, but masonry's brittle nature. If you make the trailer so it will hold the weight without deflection, than it will break since things have to move. Get the trailer stiff enough and the masonry part will crack, since it is brittle and road travel is incredibly brutal.

Maybe a hybrid system where you use a metalbestos chimney with smallish masonry stove? Still, one crack and the next time you light it you could send fumes back into your home on wheels that might literally kill you.

I would probably just go with a steel stove and chimney if you plan on a moving house.

I agree with the others. A traditional masonry hearth is too heavy and too brittle for travel.

A steel or cast iron hearth with some modern insulation around it may be possible, but I think you might be better off in this situation to get a more traditional stove, rather than an open hearth. If you want the ambiance or style of cooking, maybe just making a campfire nearby when you park could work?

What do y'all think about sand as a thermal mass?  If I weld up the fireplace out of plate and box in behind it and fill with sand. The sand might settle but it wont "crack" and I would set it up to dump all the sand  if I move and then refill the cavity when set up.  The open hearth is definitely integral. I'll be using flint and steel to let a fire. If that gets old it's not a big leap to add a wood stove and oil lamps.  I know a hybrid 12 volt/propane system is the bee's knees, compiled with a bic....

compiled with a bic....

What does this mean please?
Sand sounds like a great idea.

It might be possible to cast a fireplace - whether monolithic or in pieces - using aerated concrete.

Darwin, of the HoneyDo Carpenter YouTube channel, has made a lightweight box stove from aerated concrete.  You could check out his channel - he's got lots of videos of his various experiments with lightweight concrete for several structural applications, in addition to the stove.

Maybe a radiant style fireplace - Rumfordesque?  There are pretty standard dimensions/proportions available for Rumford fireplaces that will heat and draw well.

I don't know that this would work, but it seems like a definite "maybe"!

John C Daley wrote:

compiled with a bic....

What does this mean please?
Sand sounds like a great idea.

The bic is a butane lighter kept close to every propane lamp. You turn on the 12 volt lights long enough to find the lighter.

There are lots of portable steel forge plans/ideas that would work as is or slightly modified.

Kevin Olson wrote:It might be possible to cast a fireplace - whether monolithic or in pieces - using aerated concrete.

Darwin, of the HoneyDo Carpenter YouTube channel, has made a lightweight box stove from aerated concrete.  You could check out his channel - he's got lots of videos of his various experiments with lightweight concrete for several structural applications, in addition to the stove.

Maybe a radiant style fireplace - Rumfordesque?  There are pretty standard dimensions/proportions available for Rumford fireplaces that will heat and draw well.

I don't know that this would work, but it seems like a definite "maybe"!

A monolithic casting might survive a road trip.   I've got some engineering to figure out, like is how do I work with "thermal mass" differences between metal and masonry.   Being that I'm in a place that gets hot in the summer, it might be nice to be able to vent extra heat out of the back of the fireplace to the exterior, so that it can actually be used   in the summer.  I've also decided that I'm going to have to build a little bread oven into the hearth assembly, which will need more mass to hold heat.

My first thought was a Rumford design, but that is not based on any actual experience running one, just standing around   with a bunch of carpenters after the masons had finished one.  I'm not sure if the efficiency's of a Rumford will scale to heating such a small space, and I'm not sure I actually want to maximize the radiant heat into a small room in the summer.

The one room design will need a bit of tweeking.  Going with an 8x20 trailer, I'd make the main room 8x16 with an 8x4 covered porch/screen/mud room on the back.  The attic/loft I would attempt to use for heat regulation with hatches and vents.   Old houses in the south had high ceilings for a reason.

Another big engineering question will be how light can make the whole structure including the stove.  I'm thinking some sort of light "timber frame" with the walls and roof being  foam sandwiched between a pine ship lap interior and lath and cedar shingle exterior. It might make sense to ad a thin layer of plywood sheathing to that mix to give real rigidity.   Goal would be to make the whole structure light enough to use a recycled travel trailer frame. but there's a lot of numbers I need to confirm before comitting to that idea. There's a few available locally, so It seems worth it to actual do the math at some point.  

I think you have conflicting design objectives here that might cause you issues.

1) A hearth designed specifically for cooking has quite different elements than one designed for space heating. When cooking you want to focus heat on your pots and pans, with minimal heat to the environment. A smaller, carefully controlled burn that is only used for the duration of the meal.  A larger wood fired range is likely to overheat your tiny space if you heat the whole thing up to cooking temperatures.

2) You mention wanting to be able to heat the space with wood - this implies either thermal storage, or a small fire fed continually over a longer period of time. Thermal storage is difficult in a tiny cabin on wheels, because the mass needed is itself an engineering challenge.  A smaller fire fed more regularly would work great... but one sized appropriately for the space is likely to be too small for regular cooking.

In your shoes I would be investigating rocket cookstoves (as opposed to thermal mass heaters). They work brilliantly if you have a suitable supply of dry sticks, You would need to think carefully about your flue arrangement so you don't smoke yourselves out while lighting/cooking.

Throwing out some other ideas:

Assuming your space is well insulated and generally snug, you might consider an outdoor fire and use pipes to duct hot air inside. You would ideally only need to use it during extreme cold.

This is an example of a (temporary) setup that uses ducting to bring hot air in from outside a tent.

Michael Cox wrote:I think you have conflicting design objectives here that might cause you issues.

The objective is to have a small structure similar to Thoreau's  Walden cabin with a small open cooking hearth, on a trailer.  

The hearth is an engineering challenge.  I think there's got to be an elegant way to add removable thermal mass to a built in steel hearth.

The windows are another challenge.  Big  wood frames windows are not going to go down the highway. They would likely have to be removed and protected during transit.   I'd also design them so that they open and have screens, because at the moment I'm south of the Mason Dixon.

 One scenario for its use is zoneing restrictions that allow  trailers on "hunting camps' for 6 months of the year. I live in an area with more unbuildable properties than properties with structures.   I'm not sure if having 2 adjacent lots and a come-along for the commute would work, but it might...

R Scott wrote:There are lots of portable steel forge plans/ideas that would work as is or slightly modified.

I found a few welded outdoor Argentinian cooking hearths with a fire box and short chimney. They are more of a horizontal layout for roasting meat. With gizmos.  Found it..



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Here's last winters out door fire place.  It's been neglected, and with the drought and fire warnings, Im waiting for rain before burning again.

I'm rummaging around the web trying to figure tis one out.  I ran it past some folks at a wood stove forum and got some constructive criticism and a few more ideas.  Here's a link for any one at all intrigued:

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