Is this an absurd idea?

Hi everyone…

My understanding of stoves is slightly better than non-existent. My skill and experience in masonry is even worse. My budget is very tight as well. So building a Vortex stove or purchasing a ready made plan seems not to be an option.

Hence I'm trying to conceive a second or third best option as can be seen in the attached image (in reverse order). Is this an absurd idea of a stove? It's a heavily bastardized version of the Vortex stove; basically, just two layers of mass under the firebox/ashbox.

If budget allows I want to use firebricks all around (appr 60 bricks) for durability (same thermal behaviour, expansion - contraction).

It is to heat "evenly" two rooms: a 24 m2 (258 sq foot) room in the first floor –with a 120 cm (4') deep, spread foot foundation (a reinforced concrete unibody, because of the catastrophic earthquake zone)– and the room just above with the same dimensions by means of two vents for hot air transfer and cold air return.

The house itself is a reinforced concrete construction, moderately insulated I suppose.

Climate, daily mean °C (°F):
Dec 8.3 (46.9), Jan-Feb 6 (42., Mar 7.7 (45.9), Apr 12 (53.6)

For the last couple of years it's been warmer than the above averages, with a few days around or under 0°C (32°F), though quite windy days and nights are not rare.

If it's not an absurd idea and is worth the hassle and "safe":

1. How thick should the bottom, foundation layer be? And should it be insulated? With calcium silicate boards?

2. Are fused cast mullite bricks (http://www.atestugla.com/fused-cast-mullite-bricks-and-blocks.html) or one of those refractory castables (presuming they're not very expensive) better for firebox? Without additional calcium silicate boards insulation?

3. How thick should the firebox walls be?

4. I can't feed woods from top, cook top and get away without a front door for wood feeding, can I?

5. What should the sizes and positions of the hot air transfer and cold air return vents be to evenly heat the upstairs room with the same dimensions?

6. Anything else?

Any input or pointer greatly appreciated.

Hello Acar and welcome to permies!    First, there is no absurd question, only a wondering mind that has not yet experienced the questions being asked. With that said, I would highly recommend to get some experience with a basic rocket stove first and learn first hand how it operates. Dry stacking bricks in your backyard (or somewhere else safe for burning) allows for modifications that will allow you to discover what happens when the burn tunnel is too long?....when the heat riser is too short? ...how important surface area is,  etc.
Building one from clay is also fun because you can alter the shape more using round forms and it gives you a taste of working with cob which is a skill that will come in handy later if you want to use it as a material to build part of your mass with.
The go-to book we often recommend from novice to pro is The Rocket Mass Heater builders guide
So much info in one place that saves a lot of hunting around to get.
I hope you are not discouraged by not getting exactly what you want right away. This forum is full of peoples stories, successes and learning curves which can also be very helpful.
I wish you all the best in your findings!

Thank you, Gerry. I gather it's not a wise idea!

Be encouraged that alternative methods of heating and cooking with wood as a fuel source are definitely possible.  Whether or not your design is safe or effective can be best determined by first building a "known good" design.  From this you would learn a great deal about the basic principles of "rocket" heating and cooking solutions, both of which are based on centuries-old masonry solutions from eastern and northern Europe.  Almost all of the ideas, good and bad, have already been tried.  The good news is the lessons have been learned and you can benefit from those.  Once you have learned what DOES work, you'll have a better understanding of why your idea may or may not work, and you'll know how to gauge the relative degree of success you achieve.

We have long appreciated - KISS (keep it so simple). Finding a copy of the old Wood Heat (John Vivian) book could help you fill in the blanks for meeting your needs in as efficient a manner as possible.