4in system for a 100sq ft:

Hi all I am looking for some support.

I live in the UK and am moving into a tini space (109sq ft) I need to get an efficient heating system in that will run on small scrap wood and has some mass to retain heat over night. I have very little space for a log store so efficient is key.

My thinking is to put in a very small RMH with just a small amount of mass that I can top up morning and evening just to keep the winter chill at bay overnight.

There is currently a 4in flue in place and I'd love to use it if it's viable to do a 4in system as taking it out would be a massive job.

Alternatively I've been thinking about a pocket rocket with mass built in around the barrel on 3 sides and underneath if this would work better for such a small space.

I'd love to hear any thoughts or pointers to examples of 4in systems

Thanks

L. Lines : A lot of martial to get through - Lets start !The Rocket Mass Heater RMH is a very efficient Space Heater that when well built is self correcting
and also alerts its operator all its needs through a series of 'tells' Mostly auditory -the rockets roar - and visual clues to the temperature Your Rocket is
running at by the Color of the walls of the burn tunnel !

This efficiency comes from the high temps and resulting near complete combustion ! Make-up air 'fed' to the fire is warmed on its way to the Heat Riser
where this combustion occurs !

The amount of 'make up' air needed for a ~1400 sq ft ~ home requires an 8" System ! This 8'' piping will have an interior space of 50.24 Sq. inches and
an inside circumference of 25.12 inches notice the 2 : 1 ratio !

The amount of 'make up' air needed for a ~100~ sq ft home works with a 6'' RMH system.This 6'' piping will have an interior space of 28.25 sq in. and
an inside circumference of 18.84 inches here the ratio is closer to 2 : 3

Now the 4'' its 'Make up ' air requirement (sub 500 sq ft ) seems to be an interior space of 12.56 sq inches and an inside circumference of 12.56 sq. in.
Note the 1 : 1 ratio

When we reduced our 8'' pipe by 1/2 to 4'' we actually reduced the interior area to 1/4 - and it gets worse - Note again the ratios of space to flow air
through ! At the interior wall of Your piping you have a boundary layer where the flow of air is stalled or zero flow so when the ration is very close the
boundary layer has a much greater effect in slowing down the flow of air efficiently through Your RMH.

While a 4'' RMH is possible, it is a very fickle beast as it is running very close to its minimum requirements all the time ! every one here wants your 1st
Rocket to be a success ! Further 6 months from now we want you as a full-fledged Rocketeer to be answering questions in these Forum Threads !

When new members and future Rocketeers come to this site for advice on attempts to build their 1st RMH, generally they are steered to a 6'' system
as the smallest RMH to attempt for a 1st Build ! Most of them with much larger spaces to heat are so satisfied with their 6 '' system they never attempt
a 4 '' system !

The fine people at DragonHeaters.com or Dragon Heaters Face Book make a 4 '' kit model that guarantees a successful build every time by eliminating
the variables ! And you should look them over ( I know nothing about Their sales out of the U.S. )

The pocket rocket is much loved by Zombie Hunters, Preppers, Ice fishers and people on picket lines - where it is not uncommon to see a 55 gal drum
burning a cherry red right at the bottom and it has been known to set blacktop on fire !

As designed it is made to be used outdoors, While this is a very efficient unit with little smoke produced mo
st of the heat energy produced ends up going
up the chimney, shutting the fire down is a problem when attempting to use it indoors as you will have some amount of problems with smoke ! Immediately
after the fire is out -you are cold again !

There is also a problem with longevity of Your Pocket Rocket, in order to have Your insulation and thermal mass on the inside of your barrel to increase
the Drums longevity you will need to use at least a 30 gall drum if you can find one !

While a working 4'' RMH would seem to be your best answer, My recommendation is to identify your location in England much more specifically so that you
may make a connection with a Fellow Member who is a near neighbor with Rocket and Cob experience

For the Good of The Crafts ! Big AL

Thanks for that. Great answer with plenty to be thinking about.

The reason I was leaning towards a 4in system is mainly to do with the chimney currently in place. Ive been thinking of ways I could do a 6in system and would far rather buy the issue is chimney. Realistically I don't think I'll have time to take it out and replace before winter. Which leaves me with the problem should I put in a traditional coal stove this winter and wait until I can redo the whole thing or try with a 4in system which could well work.

My thinking to get some mass into the pocket rocket was to set a square tank in brick (ie wall around three sides of the central steel combustion chamber) and gain mass that way. Plus a fair proportion of the current chimney is brick so there would be some mass gain there as well. But still I think a RMH would work more efficiently and provide a cooking surface.

Any thoughts on whether it's worth trying for a 4in system. I'm in Kent in the South east and would love to see one in action over here if anyone knows of any

Thanks again

Mate, do a 4 inch batch, they're way less finicky!

Thanks.

Have you got any links that are worth checking out don't know much about them

Max is right, you would be probably best served with a 4" batch box system. I've built such a core recently out of vermiculite board and incorporated it in a 55 gal. barrel with a lid. And I must say, the thing turned out to be more powerful than I anticipated. The lid became hot enough to fry potatoes in a frying pan, so that's your cooking surface at a convenient height. When the whole of the barrel would be stainless steel you could do your frying on the lid itself.

The rest of the barrel got hot as well because the exhaust opening was situated low in the side. In order to gain mass you could stack firebricks inside the barrel. Probably the exhaust temperature will go up this way but it's easy to couple a small or larger barrel at the back end and have more mass in your tiny home. The vermiculite board won't last forever but hey, the cost is low and it can be replaced by a completely new core in a day.

I'll agree with Peter and Max - a 4" J-tube RMH would probably give you adequate heat if you got it built just right, but something that small would have to be fed every 5-10 minutes while burning. A batch box would give more heat in a given burn time and require less tending. If you build it carefully to the specs in that donkey32 thread, it should be reliable and not too time-consuming to tend.