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Cooking stove for 200Sqft Tiny home

 
jordan barton
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Hello folks

I am going to be building a tiny home on a round wood sled. It will be skiddable. I am wanting to only cook with wood. We currently do this with a fisher stove in the main house. And we now have a rocket oven!!! We are almost propane free!



so following the same principle in this tiny house. I would like to be able to cook with only firewood. I would also like to gain some experience making a rocket cookstove/DSR/vortex stove/ matt walker cook stove.


My main concerns are.
The floor will be Nominal 2x8s 16"OC and the flooring might be 2x4s. Will this be strong enough for one of these stoves?

it is a small space and i am wondering if this it too much of a stove for 200Sqft. How will i know?

Cooking is the main function of the stove for me.

Need more information?

Thanks for any help!

I can always create a small j-tube outside to cook on, however i would like to have the option of cooking inside for when the weather is rainy/windy.
 
Glenn Herbert
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I don't think your issue is weight-bearing so much as flexing. A masonry stove cannot tolerate any flexing of the floor under it, so you will have to either ensure the house is totally rigid, or make a rigid platform to set on the floor. If you primarily want cooking use with minimal heating, you can reduce the mass to as low as you can get while holding the works. You might even make a braced metal frame/base to set the insulated refractory core in. If you have a metal shell instead of brick, you may be able to significantly reduce the footprint of the Walker tiny cookstove. Also, depending on the usage, particularly if you don't plan on being able to cook with four pots at once, you can probably scale down the Walker design to a 4" or 5" equivalent core and make the overall stove narrower.
 
jordan barton
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thanks for the reply glenn.

So is the flexing concerns all of the time? Or are the flexing concerns when/if i need to move the tiny house on skids? I figured i would need to dismantle the stove if i needed to move the tiny house.

I can always change the flooring/floor joists to accommodate a heavier stove.

Matt walkers stove seems simple in my mind. It incorporates all of the elements i would want from a stove. I am mostly concerned with it being just to dam big of a stove for such a small space.

Maybe i would be worth it for me to contact him via email.......


Would you happen to know about other small masonry stoves designs i could take a look at? The Vortex stove seems like too big of a stove. Of course i could always come up with another means of cooking food when it was to warm inside the house. I just imagine cooking beans on the stove for 4 hours would be hot!

 
thomas rubino
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Hi Jorden;  Flexing would only happen when moving the house.
Take a look at this thread. Its rather long but a good example of making a small masonry stove.
https://permies.com/t/43809/Masonry-stove-diy-build-feasible
 
Jan White
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That's about the size of our house. We've got a super basic metal box wood stove, about 15x20".  I would hate to have that thing going long enough to even boil a bit of water in the summer.  Even in winter, it's sometimes hard to run it hot enough for long enough to cook anything substantial without heating the house up unreasonably. I realize you'll have the mass absorbing heat, but still, it might be tough to make it work all year.

Another thing about cooking in such a small space is it produces a lot of humidity. And all your clothes smell like whatever you cooked for three days afterwards.
 
D Nikolls
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Jan White wrote:That's about the size of our house. We've got a super basic metal box wood stove, about 15x20".  I would hate to have that thing going long enough to even boil a bit of water in the summer.  Even in winter, it's sometimes hard to run it hot enough for long enough to cook anything substantial without heating the house up unreasonably. I realize you'll have the mass absorbing heat, but still, it might be tough to make it work all year.

Another thing about cooking in such a small space is it produces a lot of humidity. And all your clothes smell like whatever you cooked for three days afterwards.



About the size of my tinyhouse too, and I really second the humidity issue. I currently cook with propane, and extended cooking times in summer is Not Good; planning to have Really Good ventilation, and ideally a way to cook outdoors most of the warmish seasons, is important.
 
jordan barton
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So i have been trying to figure out the amount of BTU/kw i will need in order to heat this space.
the plan is to have 6" rockwool in the walls and the roof. all on 2 ft centers

the floor is going to be 8 inches of rockwool. 16" o.c

I plan to have a few windows which fit inbetween the studs. maybe 2 or three windows.

I plan to make a insulated door similar to what they are doing at wheaton labs.

Peter's batch box website says i need
1824w to heat the space.

If i use the other figure i get it down to 1520w

This shows me that i need a 6 inch system according to Peter's Graph


   125 mm — 3.5 kg — 1.1 kW
   140 mm — 4.9 kg — 1.5 kW
   150 mm — 6.0 kg — 1.9 kW
   175 mm — 9.5 kg — 2.9 kW
   200 mm — 14.2 kg — 4.4 kW
   230 mm — 21.6 kg — 6.7 kW
   250 mm — 27.8 kg — 8.6 kW



When i use standard btu calculators like simplex

I get that i need 2462BTUs to heat the space. which translates to 0.72154089718 watts.

why the difference?

This website shows i need 8100 btus which translates to 2.3738754132 watts

I am royally confused.

almost every btu calculator i have looked at is different.
 
D Nikolls
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I think the first three numbers are just... wrong, by a fair bit.

8100BTUs sounds like a reasonable number to target for a propane or electric unit with a bit of extra capacity. I don't know that there is an exact conversion to wood, but I'd round up again..





My tinyhouse is 28ft long by 8.5 wide, no loft. 2x8 floor, 2x6 roof, 2x4 walls, all with roxul. Additional 1.5" roxul on the outside of the walls. So, very similar, a bit less insulation in the walls, which the broken thermal bridging in my build probably more or less balances out..?

Figure my site gets a little colder than yours, I'm in the comox valley, not too near the water.


I don't have my HRV installed yet, so there is a bit of loss to a cracked window in the winter, but otherwise it's pretty tight, and has relatively little window area at about 35 square feet.




My direct vent propane heater has a rated output of 8800 BTU.
So, that is about a 2.6KW rated output.

Judging by duty cycle, it's had a little capacity in reserve down to the lowest temps I have seen here, -10c nighttime lows; it has never failed to keep the house as warm as I want, which is usually pretty darn warm since I spend all winter struggling to dry out A) lots of wet work clothing, and B) the house itself due to all this humidity. Maybe it has 15% reserve on the coldest nights?


Obviously this is not a science, but I am at least confident that it has SOME headroom left, and that it does not have anywhere near 50% reserve capacity.

My feeling is that a 6000BTU output would be getting down to the minimum for those coldest nights. It's already a moderately slow process to warm the house from 5C in cold weather...




I am hoping to get a woodstove installed this summer, to cut propane out barring backup and extended absences. I am thinking a 5KW stove.

A 2.6kw rated woodstove would put a LOT less heat into the space in 24h vs the 2.6KW propane unit; there is some time wasted as the fire gets going, then somewhat variable heat output as the fire hums along, fades, is fed, hums along, fades... Most days, I'll be outside, and the fire will probably be embers or dead when I get back at lunch and dinner... All extra pronounced with such a small stove needing relatively frequent feeding.

And then you go to bed and the heat fades out in... 3 hours, maybe? So, I am rounding up, to try and get a similar total daily BTU output...

OTOH, you can warm yourself directly in front of a woodstove much more effectively; the heat from the propane unit goes up, no real radiative heating to speak of...




(Unrelated: If you are not striving to be under highway max height, why not a thicker ceiling? A good place to pick up some efficiency.. I am intending to redo mine with much more insulation now that I don't intend the house to travel highways again.)
 
jordan barton
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D Nikolls wrote:
I think the first three numbers are just... wrong, by a fair bit.

8100BTUs sounds like a reasonable number to target for a propane or electric unit with a bit of extra capacity. I don't know that there is an exact conversion to wood, but I'd round up again..


My tinyhouse is 28ft long by 8.5 wide, no loft. 2x8 floor, 2x6 roof, 2x4 walls, all with roxul. Additional 1.5" roxul on the outside of the walls. So, very similar, a bit less insulation in the walls, which the broken thermal bridging in my build probably more or less balances out..?

Figure my site gets a little colder than yours, I'm in the comox valley, not too near the water.


I don't have my HRV installed yet, so there is a bit of loss to a cracked window in the winter, but otherwise it's pretty tight, and has relatively little window area at about 35 square feet.


My direct vent propane heater has a rated output of 8800 BTU.
So, that is about a 2.6KW rated output.

Judging by duty cycle, it's had a little capacity in reserve down to the lowest temps I have seen here, -10c nighttime lows; it has never failed to keep the house as warm as I want, which is usually pretty darn warm since I spend all winter struggling to dry out A) lots of wet work clothing, and B) the house itself due to all this humidity. Maybe it has 15% reserve on the coldest nights?


Obviously this is not a science, but I am at least confident that it has SOME headroom left, and that it does not have anywhere near 50% reserve capacity.

My feeling is that a 6000BTU output would be getting down to the minimum for those coldest nights. It's already a moderately slow process to warm the house from 5C in cold weather...


I am hoping to get a woodstove installed this summer, to cut propane out barring backup and extended absences. I am thinking a 5KW stove.

A 2.6kw rated woodstove would put a LOT less heat into the space in 24h vs the 2.6KW propane unit; there is some time wasted as the fire gets going, then somewhat variable heat output as the fire hums along, fades, is fed, hums along, fades... Most days, I'll be outside, and the fire will probably be embers or dead when I get back at lunch and dinner... All extra pronounced with such a small stove needing relatively frequent feeding.

And then you go to bed and the heat fades out in... 3 hours, maybe? So, I am rounding up, to try and get a similar total daily BTU output...

OTOH, you can warm yourself directly in front of a woodstove much more effectively; the heat from the propane unit goes up, no real radiative heating to speak of...

(Unrelated: If you are not striving to be under highway max height, why not a thicker ceiling? A good place to pick up some efficiency.. I am intending to redo mine with much more insulation now that I don't intend the house to travel highways again.)



thanks D for the reply

Yea the numbers were throwing me off a great deal. I however am assuming heating with propane vs heating with a masonry type stove would be much different. The propane heats the air where as the stove would radiate the heat it stored during firing. I expect the btus to heat with propane to be much higher.
During the winter i am at home most of the time only leaving to go to work or social functions. Max i would be away is 6+ hours. I also have goats to manage so i need to be here morning and at night time. So i will most likely not need to warm it up from 5*C i hope!

Last winter we received a -10 without snow for a few days. in the current house i am in. it made the floor really cold. The cold would travel up my chair and cool my body down. i had to insulate my chair in order to be able to sit down for extended periods.  I was reading 48*F with my infrared gun on the floor!  To help mitigate the cold spell. I added about 100 clay bricks around our wood stove and changed the baffle so the stove became much hotter before leaving thru the chimney. That helped a lot. Now i could fire the stove at hot temps without losing all the heat to the air.

Yea i could go with a more insulated roof, However i was thinking with it being such a small space, if i need to run the stove a little longer due to that i could live with it. Especially because i work at a sawmill and get all the offcut/scrap lumber.

At the moment i am thinking i have a pretty well insulated space and would like to see how it performs. I was thinking i could change it if required. How do you plan on changing your roof? taking the roof off and adding 2x10 rafters?
One thing i could do is make the ceiling somewhat suspended and add more insulation once the rest of the building is closed in.
I did just spend 2133.60 dollars on insulation, tyvex and vapour barrier!

The tiny house might be moved. maybe not moved at all. its unclear at the moment. the biggest concern actually has to do with our narrow roads. 10 feet is really the max i can make this building and still be able to skid it around. There might be roads where i would not be able to go down them.
 
jordan barton
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Location: Coastal Salish Sea area, British Columbia - USDA zone 8-9
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Hey d

I found this website Build it solar

They have a much more indepth heat loss calculator

Maybe you will  find it useful

Here is what mine reported
Screen-Shot-2021-06-15-at-10.33.37-AM.png
[Thumbnail for Screen-Shot-2021-06-15-at-10.33.37-AM.png]
Screen-Shot-2021-06-15-at-10.33.47-AM.png
[Thumbnail for Screen-Shot-2021-06-15-at-10.33.47-AM.png]
 
We don't have time for this. We've gotta save the moon! Or check this out:
Solar Dehydrator Plans - Combo Package download
https://permies.com/t/solar-dehydrator
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