Rocket stove questions

I just discovered the term (Rocket Stove) a few days ago and am wondering about the biggest size (diam.) of stick or lumber that can be used in one of these?

All the info I have found seems like one would have to constantly keep stoking one of these, talking about the J style mass heaters. What is the burn time between loading the stove?

I have been heating 2,000 Sq.. foot with my Quadrifire wood burner for a few years now in my rebuilt super insulated home (10'' thick walls.) The stove is centrally located in the L shaped house, but all of these type stoves use considerable amounts of wood.

I love the idea of burning less wood.
(Also working on a thermosiphon wood heater for the hot tub.) Thinking of trying my first type stove here. Have an old aluminum pressure cooker  to use as the water heater pot. Drilled the side and top of the pot for copper fittings for the water lines to the hot tub. Now want to build the stove. But again don't want to have to baby sit it feeding sticks.


Also have a partially finished HAWT from Ed Lenz at Windstuffnow............

Woodman, a rocket stove is like a masonry stove/Russian fireplace in that you build a hot fire for an hour or two to get the mass heated up, then let the fire go out (blocking the opening so you don't get cool air pulled through the system) and go on the heat radiated from the mass for up to 24 hours.  In really cold weather you might have to fire the stove twice a day, in cool weather only once a day, and in fluctuating cool/warm weather (like fall and late spring) it might only need to be fired every other day or as needed.  So it's not like you need to keep a fire going all night long (in fact, from what I've seen, you should let the fire go out at night).  You want smallish pieces of wood to burn hot and fast and heat all the mass up, not big chunks to hold a fire for a long time.

Kathleen

The biggest system I have heard of is "a ten inch system" meaning that the inner ducts are ten inches in diameter.  And that would mean that the wood feed tube would be about the same. 

But my impression is that a ten inch system is rare and not for the beginner.  An eight inch system is far more common, is for the beginner and probably what you want to build.  (again, my impression could be wrong)

So, you could probably put a stick in that with a seven inch diameter. 

You might burn a fire for a couple of hours and then bask i the glow of that warmth for a day or two. 

I would guess that you will probably have two or three times fewer fires, and the fires you do have will use half the wood. 

Erica will hopefully chime in here soon and she'll have much better info than me.

Speaking of rocket stoves and heating larger spaces, what is the largest home anyone has successfully used one in? And what type of climate is this in?

I ask as I remember seeing a video of Flemming Abrahamsson (I believe) who said something that lead me to believe rocket stoves were not that well suited to anything but very small cottages.

I would like to hear the answer to that question too!

However, the general math runs like this:

When you use a conventional wood stove, how much heat goes out the chimney?  70%?  90%? 

And with a rocket mass heater, it would seem that hardly any heat leaves the exhaust. 

Further, it is possible to run your mass heater more often. 

rusty wrote:
Speaking of rocket stoves and heating larger spaces, what is the largest home anyone has successfully used one in? And what type of climate is this in?

I ask as I remember seeing a video of Flemming Abrahamsson (I believe) who said something that lead me to believe rocket stoves were not that well suited to anything but very small cottages.

Biggest home Ernie has heard of so far was about 4,000 sf, down in North Carolina. 
There've been some other substantial-sized spaces that used them, too - worksheds and such. 
You also have to remember that one of the key advantages is being able to experience direct contact with the warm (not overly hot) thermal mass.  If you heat the people to a comfortable warmth, they don't care what temperature the house is over by the window or ceiling. 

I don't know any mathematical conversion to determine what size of rocket heater could heat what size of conventional house.  People tend to practice a few times, then get a handle on it, and build what they think will work. 
If it's not enough, people often use their 'old' heater as a booster on cold days.  (Don't tear out your stove to build a rocket mass heater; with both in place, you have a very fair test to see which you prefer.)
Woodstoves are nice for instant heat, first day home from vacation, and watch-the-fire cheer.  Rocket heaters are better when you're there to fire it every few days, maintaining constant temperature, but don't want to be stuck watching the fire for hours on end when you need to be doing other things. 

If it's too much they fire it less often, but most people don't over-build on their first attempt because it's more work. 
(One exception is a 12" sub-floor heater that one of the researchers built to double as an aluminum smelter... and then he finished his floor with a beeswax polish.  Now the heater melts the floor.  He says he just  doesn't walk on the floor until the wax sets again...not a solution for the average family man, I'm afraid.)

It's a tinkerer's stove.  You tinker with it.

When it comes to hot water boilers and re-rigging them up for experiments:  please don't blow yourself up. 

The guy I know who successfully made a recirculating hot-water heater with a rocket stove was previously trained on plumbing, engine restoration, and superheated-steam hydraulics.

I encourage people who don't have that kind of background to stick with open systems.  I don't know your expertise, so if you are a registered boilermaker, don't mind me.
A boiling teakettle can heat a surprising amount of bath.  Bigger pots (or a whole tub) can be heated directly, without risk of explosion.

If you do a hypocaust-type "people cooker," with the fire directly under the hot tub, consider including a wooden seat or floor so they don't get a fried behind.  Enameled or not, metal tubs get pretty darn hot. 

I wonder if anyone's tried the leather-bag version of the People cooker: a giant version of the Scouts/indian trick where you heat/boil water in a paper bag, basket, or leather pot (the water's temperature, and the little bit that seeps through the pores, keeps the bag from burning).


If you do a "hot water tank" type, where the water comes in from a heated tank and you mix it to suit, build in safeguards so that
1) It's impossible for the water to boil anywhere and explode: Safety outlets or valves on the main tank should be big, robust, and difficult to disable; any smaller pipelines should be away from direct heat.
- if your temperature regulation depends on recirculating water, it needs to be impossible for the water to stop, back up, or otherwise fail to flow.  Steam explosion in copper pipe is not pretty.  You may need a "dump" option if the recirc temperature exceeds the design temp.

and

2) There's a safety-check to make sure that scalding water (over 150 degrees?) can't be dumped directly onto unsuspecting nekkid bathers.

Fried and scalded nekkid people are a lot less fun than the other kind.

There've been a few nice examples of water heaters shared around the forums, you may find some useful ideas if you look back over the past year or so.

-Erica

Hi everybody
I am here because of rocket stoves and there is a very very small comunity of users in France. So I think its better to exange more. (not easy, language,unities...)

Erica's answer is pretty good and I want to be more precice.
Woodman, it's a good idear to heat water in a close tank. But it's very dangerous and you can kill yourself, your family and destroy your house. So you're obliged  to deal with three securities.

First, you can't compress water and water expands with heat. For example a 26 gallons tank full of water at 50°F is heated at 158°F, so you've got about 26,7 gallons of water.
A security group allows this 0.7 gal to go out.

Second, you can't regulate temperature with solid fuel, so if your water is near the boiling point you need a thermic security with a probe in your tank. At 203°F the cold water goes in the tank and hot water goes out.

Third, 158°F hot water burns your skin and cook your meat so you put a mixing safety valve just after the tank and you can't have pure hot water in your home(shower...) more than 138°F

It is safe now!

More. Your question: is a rocket mass heater able to heat all my home is not a good question.

It depends on two factors. Insulation and volume implantation of the house.
The rmh works in two ways. The barel heats the room first with convection and radiation.
The convection heats air and so can move up.
Later the mass is hot and works a little bit with convection, a lot with direct conduction and a lot with infrared radiation.
Conduction and if radiation heat are local and doesn't heat air. They heats you and if rad you and the walls.

So if you want to be confortable everywhere, you have to be "seen" by the mass everywhere.

In conclusion there is an old precept in east of France (there where a lot of traditinal mass heater like in estern Europe and Russia)

To be confortable in winter, first you built your mass heater, and secondly you built the house around.

Celcius wrote:
...water expands with heat....

No offense but actually water is one of the few things that expands as it gets colder, it does not expand with heat. That is why, for example, water pipes will burst in unattended cottages over the winter if the pipes are not drained.

Well, I guess I need to correct myself. water will expand when heated at certain temps. Sorry, my bad! 

Water expands when heated. Water contracts as it cools. Somewhere around 4*C, water pulls a switch and begins expanding. This causes the pipes to burst, like CleanAndGreen said, and also allows life to survive in ponds, lakes and streams.

I like Erica's answer best - leave the tanks open and heat the water - leave the closed systems to the EXPERTS.

Heating water in a closed system - the water heats and expands and compresses whatever gas is in the tank. At some temps the water begins to turn to gas and at some point pressure is too great for the container to keep contained. You would have to rely on the pressure relief valve(s) to relieve pressure and work each and every time.

A tank from a hot water heater has pressure relief valve but also has a thermostat to regulate the amount of heat added. A wood fire under the tank depends on an operator to add or stop adding heat.