Rocket stove as backup heating system

Hello!

I have been learning a lot about rocket mass heaters and rocket stoves lately. I bought and read all the pdf Rocket mass heaters Third edition. All of this fascinates me and I find this forum very instructive!

I live in Quebec Canada where we have cheap hydroelectricity also my wife is very sensitive to hot or dry indoor temperature. So we decided that we would continue to use hydroelectricity as our main energy for home heating.

I still want to have a backup heating system during power outages. I did many research and I find rocket mass heaters and stoves quite tricky to operate. I would like my wife and older son to be able to make a fire without me worying to much. So I decided it would be better to get an epa certified wood stove even if I am mainly going to heat the cheminy with that…

But, I tought it might be possible to build a small rocket stove to put in the wood stove or just beside it. That rocket stove might have enough internal heat to be able to cleanly burn soft wood and dead wood. That way, I could buy a few wood cords each year and still be able to gather extra wood if we get a long power outage. This little rocket stove would connect inside the epa stove and use the same cheminy. Another advantage is the fact that I could play with fire and rocket stoves if I want to. I would be the only one to use it so I would not mind if that rocket stove is not covered by insurance.

What do you think about the idea? Did you ever see such rocket stove inside or beside reguler wood stove? Is there a type of wood stove I should look for to do this?

I have access to steel and stainless steel workshops.

Thank you very much and have a nice day!

Welcome Julien!  Glad to hear of your interest in rocket stoves.
I wouldn't say that the learning curve to operate a rocket stove is really any different than learning how to operate a regular wood stove effectively. Placing wood in a chamber and closing the door may be all some folks do to get some heat but then there's a lot of smoke, creosote and not much heat retention to consider.

I will try to answer your questions as best I can.
Generally, two stoves sharing the same exhaust system is not recommended - not even sure if it would be legal. However, if you had some sort of well sealed bypass to make one or the other operate (but not both at the same time), it could work. I would rather suggest building a simple rocket stove out in your back yard and having fun with it there to see for yourself what it can do, and determine for yourself just how tricky you think they are to run. You may be surprised.

Metal is not the preferred material to build a rocket stove as it sheds the heat too quickly to reach the high temperatures needed to burn all the wood gasses efficiently. If you try to insulate it, the metal breaks down and deteriorates quite quickly. You goal is to want the fire to be as hot as possible in the burn chamber until it leaves the top of the heat riser, then extract the heat.
You certainly can use metal to play with making one and try out different designs though or you could also make one from clay bricks too.

Good luck in your new adventure! Ask more questions as they arise. We are here to help.....some people even leave the light on!

Thank you very much for your reply!

I would only put the rocket stove temporairly inside or outside with a pipe running from the barel to the inside of the «regular» wood stove. Do you think that would be possible?
I would remove the rocketstove from the system when not in use. So yes it has to be made of uninsulated metal.

I can't quite picture what your describing to do.
Are you saying you'd like to direct the exhaust pipe from the rocket stove into the wood stove with its door open?
If so, I would recommend instead to put a T into your wood stove pipe and branch off that instead with a good working bypass damper to isolate ones exhaust from the other.
The other sounds kinda risky for leaks and may also provide too much drag on the system to draft properly.

Julien Beausejour wrote:
I still want to have a backup heating system during power outages. I did many research and I find rocket mass heaters and stoves quite tricky to operate. I would like my wife and older son to be able to make a fire without me worrying to much. So I decided it would be better to get an epa certified wood stove even if I am mainly going to heat the cheminy with that…

A wood stove with a nice flat top surface area works great for many applications when the power is out.

One can place pots of water on the flat top to aid in humidity in the winter as well as extra heat.  A warm moist room feels much comfortable than a warm dry room.  In a warm dry room, people still get chills.  Though don't go too wild with the most part.  A simple 4-inch sauce pan with 4-inch high wall would do really well.

Also, there are stove fans that work basically on the heat induction.  This really helps getting heat in the room/home than up the chimney.  

Depending how far up your internal wood stove stack pipe goes, one can always add pipe fins the boost the heat in the room.  Gains can be upwards to 30% more heat recovery.
Here's one good example.  https://www.amazon.com/Stovepipe-Reclaimer-Radiator-Rings-pellet/dp/B00BOQ2ATS

There are other wood stove reclaimers on the market too.   Do you recall the Bonanza saloon with the wood stove reclaimer of the old western days?   The function is, room air via natural convection floats thru the opening and gets super heated.  Thus, this works in a greatroom and not a tiny room.  It's design is for a hall or large ceiling great room.

The trouble with harvesting more heat from the stovepipe of a regular woodstove is that you risk making the exhaust cool enough that creosote condenses in the chimney and may cause chimney fires. A rocket mass heater (and to some extent a rocket stove) burns every bit of creosote to make heat, before harvesting the heat for the house; thus there is no creosote to condense and be hazardous.

Glenn Herbert wrote:The trouble with harvesting more heat from the stovepipe of a regular woodstove is that you risk making the exhaust cool enough that creosote condenses in the chimney and may cause chimney fires. A rocket mass heater (and to some extent a rocket stove) burns every bit of creosote to make heat, before harvesting the heat for the house; thus there is no creosote to condense and be hazardous.

I have ZERO problems with creosote in my EPA rated woodstove.  The trick?  Kiln Dried firewood produces no creosote, no fungus, no mold, and even less smoke.  The benefits, a better heat overall.  The other bonus is, it's not at all expensive, that is IF you build your own kiln box dryer.  Oh boy, another project folks!  

No, I don't want to earn apples or badges or whatever here and undertake another project, instead check out this link ...

Here's a great example to build your own.
https://www.wagnermeters.com/kiln-drying/solar-dried-lumber-moisture-concerns

A kiln box dryer is just another version of a solar food dehydrator.  Takes a little less effort to build since it's just a box with wired racks full of split wood.  Think of it as a sauna for a cord of wood.  

Many of the farm stores and coop stores sell campfire bundles now wrapped in plastic that have been thru a kilin dyer process.  
 
About kiln dried firewood wood
 
Kiln-dried firewood delivers a higher BTU, does not produce the potentially harmful creosote buildup in chimneys and leaves little ash. The treated wood is bug-free and contains no fungus, a relief to individuals who may suffer from allergies.  The kiln-dried wood destroys the breeding ground of the Asian Longhorned Beetle and Emerald Ash Borer, a troublesome infestation of Northern forests. Kiln-dried wood allows campers and others to transport the wood across state lines without fear of infesting the forests.

Kiln-dried firewood has ± 15% moisture compared to ± 35% moisture in seasoned firewood. Unseasoned (green) firewood can contain 50% or more moisture.