Metal open cooking hearth?

[bark-eater]

Hi all, I've got a project I'm trying to figure out if its feasible. I'd like to build my self a small cabin similar to Thoreau's on Walden pond. And I'd like to have an open hearth set up for cooking.

For a number of reasons I'll be putting this on a trailer as a "tiny house", so a masonry fire place an chimney will not be possible.

My assumption is that I can have a hearth and fire place fabricated out of steel plate and that will hold together when or if the cabin is actually moved over the road.

One of the questions I have is whether I can add some sort of removable thermal mass to the assembly, such as gravel boxed in behind the steel firebox, which could be removed to lighten the weight for transport, or just removed in the summer so that I don't get driven out by the heat.

The planned one room cabin interior would be about 7x15, which at 105 sqft will not need much heat to keep warm, so I don't think the hearth will need to throw much radiant heat, verses containing localized heat in the fire box. I've got the full 7 foot of back wall to work with so adding a small bake oven to the fabrication would be nice.

I'm well aware that this is not a practical endeavor, but as I don't think anyone has done this sort of thing before, I would appreciate any suggestions on how to put it all together in a safe manor. I'll post a couple pictures of another replica of the cabin to give an idea of what I'm after ( please disregard the little wood stove, its the fireplace with the pot crane I'm after). Thanks, Woody

 

[stoveliker]

I hope you don't need it insured.

Rather than thermal mass you'll have to think about thermal insulation of the fire; steel can contain the fire but the combustibles behind it will eventually catch fire. And with only the steel, it could even be quickly so.

So, I suggest to stock up on ceramic insulation. You can buy it on Amazon. Nasty stuff though.

 

[bark-eater]

I hope you don't need it insured.

Rather than thermal mass you'll have to think about thermal insulation of the fire; steel can contain the fire but the combustibles behind it will eventually catch fire. And with only the steel, it could even be quickly so.

So, I suggest to stock up on ceramic insulation. You can buy it on Amazon. Nasty stuff though.

At some level there doesn't need to be anything combustible behind it as the fire place and chimney are on the exterior of the structure. I'm my minds eye I would like to maintain the exterior form of the chimney stack, but it could be a sheet metal shell covering the fire box and a metalbestos chimney. I had thought about the ceramic, but at least in propane forges it gets covered in refractory cement, which might not survive a road trip. But the face of the hearth will have to have to have some sort of insulated break where it joins the wooden structure. I'll be building this on a steel frame, so the fire place can be basically free standing and not directly connected to the walls. Good point. Thank you.

 

[begreen]

I think it would be better to think of practical needs. Have a bbq for cooking outdoors over a "hearth" and put a usable stove/oven in there for year round usage. Force Ten makes some good marine units that are compact.

 

[bark-eater]

I found some outside Argentinian cooking hearths that use mechanically restrained fire bricks.

 

[begreen]

You didn't tell us that this is going to be a sauna.

 

[stoveliker]

At some level there doesn't need to be anything combustible behind it as the fire place and chimney are on the exterior of the structure. I'm my minds eye I would like to maintain the exterior form of the chimney stack, but it could be a sheet metal shell covering the fire box and a metalbestos chimney. I had thought about the ceramic, but at least in propane forges it gets covered in refractory cement, which might not survive a road trip. But the face of the hearth will have to have to have some sort of insulated break where it joins the wooden structure. I'll be building this on a steel frame, so the fire place can be basically free standing and not directly connected to the walls. Good point. Thank you.

You need insulation nonetheless because the steel (a good thermal conductor) will be touching combustibles where the structure transitions to the rest of the build.

 

[bark-eater]

You didn't tell us that this is going to be a sauna.

That's a real part of the equation. It's a very small space. I want to be able to burn very small fire to cook over. I don't want to get smoked out or baked out... I'll have 2 big windows and probably some additional adjustable vents in the roof peaks. Thermal mass will help with cooking and and baking, and as the fire place and chimney are external, slow down the direct heating of the outdoors.

 

[bark-eater]

You need insulation nonetheless because the steel (a good thermal conductor) will be touching combustibles where the structure transitions to the rest of the build.

I was going to elaborate on that. I was thinking about some sort of flexible gaskets made of welding blanket, but if I made a sock of welding blanket and filled it with fiberglass, that would work pretty well to make a 4" insulated gap. I'm trying to design this around very small fires, but that doesn't mean that some one wouldn't build a large fire in it some time.

 

[stoveliker]

Then Use rockwool (roxul), not fiberglass for this due to its higher temperature rating.

How are you determining that you have sufficient insulation to be safe?
That is a problem with set ups that are finagled together; no data and testing.

I am also not sure that a very small fire will get thermal mass up to temp to be helpful with cooking.
(I've done stick fires in cinder block stacks for cooking and it's the fire that does it, not any thermal mass.)

 

[bark-eater]

Any thoughts on using vermiculite as an insulation/ thermal mass?

 

[EbS-P]

I would set up an outdoor kitchen. Now an an option would be those suspended 70s fire pit fireplaces. That said you can do a lot with a Dutch Oven.

If it were me in a tiny house and I really wanted an authentic cooking experience I be looking at boat stoves and realizing that most cook open fire cooking will be outside.

 

[bark-eater]

Then Use rockwool (roxul), not fiberglass for this due to its higher temperature rating.

How are you determining that you have sufficient insulation to be safe?
That is a problem with set ups that are finagled together; no data and testing.

I am also not sure that a very small fire will get thermal mass up to temp to be helpful with cooking.
(I've done stick fires in cinder block stacks for cooking and it's the fire that does it, not any thermal mass.

I'm talking about 2-4 logs burned down to coals. I saw a sheet metal wood stove that was designed to be built into a wall. It as on craigslist for free. It was probably full of asbestoses and had been removed for insurance reasons, but I'll try and track down some more info. The installation manual probably hit all the relevant points.

 

[stoveliker]

Point is, are you wanting this as an authentic (museum like) thing to display (while using), or to live in it?

I see a lot of things online that one should walk away from as it might kill you...

Hence my question: will you need this thing to be insured?

 

[stoveliker]

Also, thermal mass and thermal insulation are two completely different things.

Thermal mass is supposed to get hot.
Insulation is not (beyond its surface.)

Google pyrolysis for an idea of why you need insulation around the steel box.

Thermal mass is not good insulation.

 

[bark-eater]

Also, thermal mass and thermal insulation are two completely different things.

Thermal mass is supposed to get hot.
Insulation is not (beyond its surface.)

Google pyrolysis for an idea of why you need insulation around the steel box.

Thermal mass is not good insulation.

I've seen some scary stuff behind a built in electric range. I got you on needing to isolate anything combustible from any metal connected to the hearth. With insulation. And I know the Cape Cod parable.

Assuming that cooking and heating efficiencies can be discussed apart from the acknowledged critical safety concerns, What's a good way to add thermal mass to a plate steel fire box, that will survive a road trip?

p.s. I'm not sure what kind of insurance exits for 100 sqft cabins on a trailer frame, with any kind of wood heat.

 

[EatenByLimestone]

Look into how teardrop trailers have their cooking setups. Maybe that can give you some ideas.

 

[stoveliker]

I think brick like parts (but brittle) or cast iron parts would be best for thermal mass.

 

[bark-eater]

I think brick like parts (but brittle) or cast iron parts would be best for thermal mass

I did come across a lead. Wood fired pizza ovens on trailers and food trucks "are a thing", so that's the next rabbit hole to go down...

 

[stoveliker]

Yes, good idea.
Though these often have metal rather than stick built walls.

 

[bark-eater]

And here's another variation on the theme:

 

[stoveliker]

That's just a full masonry fireplace.

 

[bark-eater]

Its an early cast iron Franklin stove. I'll assume that the original fire place was bricked in around it so that it draws up the chimney.

 

[stoveliker]

Yes, my point is that is a masonry fireplace with something out in.
The mass would be impossible for your situation.

 

[Wisco Shepherd]

Just get a cheap little wood stove. I get the vibe and aesthic but if upi are going to live in the thing I'd get a small steel top stove and be done. Or even a modern cook stove with internal oven. Kuma just came out with the appelton it's sweet.