How best to heat water using excess heat from oven

[Timothy_W]

I built a canopy under which I dry firewood. It consists of 3 walls and a roof. I thought that one open side is enough, because I will not climb into the very middle of a pile of firewood, but I will take those that I hide. If the weather is wet, then cover the open side with a tarp. It took me a long time to make such a small building for firewood, but while there were warm dry days in winter, I tried out my new cordless tools and assembled this shed literally in a day. Of course, I ordered the wood earlier, it was in my garage so as not to damp it in winter. Now, hopefully, I will always have good dry wood for the stove or for the barbecue.

[JRPizza]

Terratree, below are three posts where I have discussed IT designs - at least the way I understand how they work. The first is from my build. There are quite a few designs that get your axis of rotation and pivot point at the center of the oven - you just need to be creative. I was inspired by Gulf's design, and cannibalized an old bike rack to get the piece I used for my IT centerpoint. Did you attach a pic of your IT - I didn't see it?
Also, I built my dome on top of my floor bricks, and had read somewhere of using news paper to keep the dome bricks from adhering to the floor - possibly allowing some float. Don't know if it was needed but as I said I was just following instructions.
Lastly, I had a couple different versions of the spread sheet, but between my ability to measure an angle and replicate it on my saw I found it easier to just make two cuts on scrap and see if the bricks fit together enough to eliminate the vertical vee.

https://community.fornobravo.com/forum/pizza-oven-design-and-installation/pompeii-oven-construction/380308-39-inch-corner-build?p=381081#post381081

https://community.fornobravo.com/forum/pizza-oven-design-and-installation/tools-tips-and-techniques/3072-my-indispensible-tool-a-variation-on-a-fb-theme?p=393165#post393165

https://community.fornobravo.com/forum/pizza-oven-design-and-installation/getting-started/387771-design-phase-of-my-new-wfo-at-the-cove?p=389830#post389830

[gastagg]

Starting on my cast entry arch and vent. Here is a pic of the foam form I'll use to build the full form around. Quick job with a 1 1/2" 4'x8' sheet of foam board from Home Depot. Snowed today...next week is supposed to be above freezing. Hopefully get some work done outside next week.

[Sandy]

Re: How best to heat water using excess heat from oven

1. Convection doesn?t function when the hot object is above the cold object.

2. C. Convection
3.Their temperatures rise until they are able to radiate heat away into space as fast as it arrives from the sun.

4. I have a glass of Pepsi over ice sitting on the counter. It has been sitting there for fifteen minutes and still has ice in it. If the room temperature is 270 Celsius, what is the temperature of the Pepsi in the glass?
A. 00 Celsius B. 290 Celsius C. 13.50 Celsius D. 270 Celsius
there is mistake in stating this problem. Pepsi will evoporate, and cannot exist in liquid form at 270* Celsius. you must say 270 Kelvin, than anser is A: 00 celsius.

5.Heating the water in an opened container at the top of a high mountain where the pressure is less than 760 mm Hg.

6.Add heat and reduce pressure on ice.

7. you mean to say that the water in the tub will freez, than ans is 0 * C

8. Put the lid under warm water for a few minutes, but don?t let too much water hit the bottle

9. To avoid heat transfer to the colder object by conduction.
10. Radiation heat transfer

[david s]

Re: How best to heat water using excess heat from oven

Thanks for that, it's making me even more keen to get tis project beyond a mind plan and start committing to some work. Going to Pompeii in Oct. that should also generate some interest.
Dave

[dmun]

Re: How best to heat water using excess heat from oven

The romans had this very idea for heating their baths, the hypocaust.





No word on how they kept the water out of the firebox.

[david s]

Re: How best to heat water using excess heat from oven

my idea was to use the dome merely as a heat generator to heat the water rather than as a cooking oven. I would probably make the dome in cartable and make it fairly thin, about 1.5" thick I would guess.

[brucefehring]

Re: How best to heat water using excess heat from oven

David- I love the look, but am unsure of how practical such an idea might be.

Would the water get hot enough and, if it did (because the insulative layer on top of the dome was thin enough), would you be robbing the oven of so much heat that proper cooking temperatures would impossible to achieve?

My concern about heat loss has sent me into a different direction. Our property is private acreage with plenty of wood. Off the downwind corner of the pavilion which will house the bread oven will be a fire pit for "campfires". We have an old cast iron tub which will be placed up on blocks inside the pit at the edge. When I want a soak, I'll build a fire directly below the tub to heat it up. Not quite a hot tub, but big enough to soothe one man's aching muscles!

Good luck with whatever you attempt.

Aloha, Bruce

[david s]

Re: How best to heat water using excess heat from oven

This is avery rough idea of what I had in mind.

[dmun]

Re: How best to heat water using excess heat from oven

are you saying that you think even less heat is transferred to the outside of the insulative layer, and thus it would not even be warm to the touch?

Bingo. A properly insulated oven will not be hot except near the vent and opening. Of course we all know that energy is neither created nor destroyed, and the heat has to go somewhere, but it is dispersed so slowly and diffusely that heating water with it seems to be a non-starter.

They make nice little immersion units for wood fired heating of hot tubs. Seems like a more practical idea to me.

[brucefehring]

Re: How best to heat water using excess heat from oven

Hi Ken. Thanks for that feedback. When you say that the insulation now likely works better now that the whole thing has dried out, are you saying that you think even less heat is transferred to the outside of the insulative layer, and thus it would not even be warm to the touch?

Thanks, Bruce

[brucefehring]

Re: How best to heat water using excess heat from oven

David- Thanks for the input. I pondered a similar idea. The concerns that came to mind were 1) making sure that the weight of water plus body (-ies) plus tub were properly supported by the substructure and 2) that smoke might render the tub unusable at times when would was actually burning.

I'm hoping that others out there with any experience in trying to create a warm outdoor soak with some of the generated heat will share their experience...

Bruce

[david s]

Re: How best to heat water using excess heat from oven

I have been mulling over an idea of building a spa over a WFO with a 1" layer of vermicrete between the dome and the spa so the heat is released a little more gently, hence less problems with resulting expansion, cracking and excessive heat conduction. I thought building a thin ferrocement structure over the vermicreted dome and then following this form so the spa has a dome rising in the centre. Light a fire in the chamber and come back a couple of hours later to a nice warm tub.

[Ken524]

Re: How best to heat water using excess heat from oven

Bruce,

That's VERY similar to how my dome is insulated. 2"-4" blanket with 4" of vermiculite/cement on top of that.

Before I built my enclosure, I fired the oven a few times. The vermiculite was ambient temp while cooking pizza. Several hours later it was warm, but not hot to the touch. The insulation likely works even better now that the oven has been fully cured and there is no more moisture in the bricks, blanket or vermiculite.

[brucefehring]

Re: How best to heat water using excess heat from oven

OK, thanks, fellas. I am ALMOST convinced that a heat exchanger built into the chimney is the way to go. However, not quite...

We intend to have a thermal blanket and 4" of vermiculite insulation over the top of the dome. Because we intend to fill up the entire square space around and above the dome with insulation, there will be as much as 12" of insulation from the closest point of the dome to furthest reaches of insulated space.

How about a guesstimate, given a temperature of 800F degrees at the dome firebrick, of how hot the vermiculite insulation would be at 4" from the dome? at 6"? at 9"? at 12"?

Many thanks, Bruce