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room with liberator rocket mass heater will get too hot?

 
Posts: 19
Location: Philadelphia, PA
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Hi, I am considering purchasing the Liberator rocket mass heater - https://rocketheater.com/products/the-liberator-gen-2-without-hopper - and I would like to integrate it with thermal mass. The house is 2 stories with a basement. There is an additional room in the back of the house which is a later attachment on slab, no basement below. This additional room is 28' long, 16' wide, and has a 10' opening to the rest of the house. Although this room is not the most centrally located (which would be ideal), it has no basement, so there's no need to add structural support, something we might need to do were we to install it elsewhere. I had a wood stove installer come to my house, and he mentioned that the Liberator, since it gets very hot, might make the room it's installed in uninhabitable with very high, sweat-inducing temperatures.

Does anyone here with experience of rocket mass heaters or the Liberator in general have any guidance on this? I am a newbie when it comes to all things firewood.

We spend a lot of time in this additional room and the adjacent kitchen, so the plan was to spend a lot of time in this room and the kitchen during the winter while the stove is running, but if it's too hot to really be in, then the plan doesn't compute. Ideally the heat would spread through the house & even upstairs a bit, but it's hard to tell if that'll really happen.

Happy to provide a floor plan if that would shed more light.
 
rocket scientist
Posts: 6317
Location: latitude 47 N.W. montana zone 6A
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Hi Boris;
I do not have direct experience with a liberator stove but I have plenty with rocket mass heaters.
If you build a mass to hold your heat then you should not need to have the liberator burning all the time like you would with a regular box stove.
Any running wood burner will be hot sitting near it, as far as the sweltering hot your stove guy talked about well I doubt he has ever been around a wood-heated mass before. He is used to a wood burner that gets lit in the fall and does not go out until spring. That kind of wood burning would be where people start "damping down"  a box stove... that creates all the nasty smoke and creosote that plugs chimneys and starts chimney fires. If you run a box stove wide open like an RMH is run, it definitely would run you out of the room.
Will this stove heat throughout your home?
That depends on many variables.  
How well insulated your home is.
How open is your home design, can warm air freely move around?
Ceiling fans and box fans can help.

The bottom line with a mass heater is you do not need to burn the stove continuously.
They run wide open anytime they are lit (no damper allowed) they create bunches of heat that then is stored in your mass to be slowly released.
That is how they get such great wood milage compared to a box stove.
Light in the morning for a few hours (or less) with a home as large sounding as yours you might light it again at noon and again in the evening.
Depending on your climate and how cold it gets and stays.
If you have steady hard winds in your area and your home is not tight that affects how well this works and how often you need to burn it.
I assume there is some kind of existing heat system in place that you can use as a backup?

You will need to talk to the liberator guys to learn how much horizontal piping a liberator can push thru a mass.
What were you thinking to use as your mass?



 
Boris Kerzner
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Location: Philadelphia, PA
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Thanks Thomas!

Okay, it sounds like he may have been comparing to a conventional wood stove he grew up with. So it sounds like while it's burning it'll be hot, but when it's not burning and the thermal mass is the primary source of heat, it'll be fine.

The Liberator's user manual says that the "horizontal length running through the thermal mass can not exceed 12' feet regardless of the height of the chimney", so I was thinking a box 6' long with the heat-exchanging pipe folded once. I just bought "The Rocket Mass Heater Builders Guide" to read, so still learning, but currently thinking about a box full of gravel with pipe for thermal mass. The room is a classic suburban carpeted room with wood paneling on the walls, so this is more of a retrofit, and I want the aesthetics to make sense, and I want to be able to disassemble the mass if need be. If it's cob, it's permanent, and I'm worried that the value of the home could be lowered, if a potential buyer is uninterested. Open to suggestions, because just starting to think about this. I should add that the room already has a wood stove from prior owners. It's kinda old and was seldom used, but it already sits on a layer of brick. So the new rocket mass heater would be replacing that stove.
 
Rocket Scientist
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Location: Guernsey a small island near France.
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Hi Bois, What you  want your stove to heat up is a dense mass, the more consolidated  and dense  the mass the better, so things like gravel or even pebbles are not the best because they will be surrounded with air which is an insulator!
Pebbles have been used but you can not expect to get the best results with any loose material.

For example … Concrete blocks are not very good but brick is, sand is not very good but water is….

You will gain a lot of knowledge by reading as much as you can before making decisions.
 
thomas rubino
rocket scientist
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Hi Boris;
So 12' of horizontal pipe is not much.
A standard 6" J tube rocket can push 30' an 8" J tube pushes 50'
As you will see when you get the builders guide.  Each 90-degree turn is a 5' deduction, so making a 180-degree turn will use up 10' of your 12' allowed.
So to use a mass you will want a 12' straight pipe run not a 6' doubled back.

Now let's talk about your mass.
Forget about building the entire thing with cob.   Cob benches are beautiful but certainly not acceptable to your average adult.
A question, do you object to red brick in your living room?
Your entire mass can be contained by a red brick wall/box.
Now let's talk about how you fill that box.  On the very floor, you will want insulation. We want that heat to spread sideways and up not down trying to heat the earth.  Even if your slab is insulated you would want a layer of sand or perlite to keep from trying to heat the slab.
The washed gravel fill does work. However, it is not that efficient at holding heat.
Too many small voids that let heat escape, which might seem OK as it is going into your home, but the small stones do not hold heat very well or very long.  
You want large stones, as big as you can easily move.   Then you need a material to fill any voids between the stones.
Small amounts of cob (clay/sand mix) works well but simple dirt can be used if you like. A plastic liner could be put down to aid cleanup if you chose to remove the mass later.




 
Boris Kerzner
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Location: Philadelphia, PA
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Oh, I see, so for the greatest efficiency of the thermal mass you would want to utilize the full 12', so the chimney would not be right above the stove, as in typical stoves, and the stove I currently have at the house. Hmm. Okay, so per what Fox James was saying, I look forward to receiving the book in the mail and reading more. Thanks to both of you for steering me away from gravel / small pebbles fill due to its lower efficiency.
 
pollinator
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thomas rubino wrote:Hi Boris;
So 12' of horizontal pipe is not much.
A standard 6" J tube rocket can push 30' an 8" J tube pushes 50'
As you will see when you get the builders guide.  Each 90-degree turn is a 5' deduction, so making a 180-degree turn will use up 10' of your 12' allowed.
So to use a mass you will want a 12' straight pipe run not a 6' doubled back.

Now let's talk about your mass.
Forget about building the entire thing with cob.   Cob benches are beautiful but certainly not acceptable to your average adult.
A question, do you object to red brick in your living room?
Your entire mass can be contained by a red brick wall/box.
Now let's talk about how you fill that box.  On the very floor, you will want insulation. We want that heat to spread sideways and up not down trying to heat the earth.  Even if your slab is insulated you would want a layer of sand or perlite to keep from trying to heat the slab.
The washed gravel fill does work. However, it is not that efficient at holding heat.
Too many small voids that let heat escape, which might seem OK as it is going into your home, but the small stones do not hold heat very well or very long.  
You want large stones, as big as you can easily move.   Then you need a material to fill any voids between the stones.
Small amounts of cob (clay/sand mix) works well but simple dirt can be used if you like. A plastic liner could be put down to aid cleanup if you chose to remove the mass later.



I really need to come do a workshop with you.
 
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