Detached mass heater?

I'd like to have a batchbox RMH. But I'm afraid that something will fail someday. So is the insurance company - if the house burns down as a result of not using a certified fireplace, they will not cover.
So I figured I'd like the stove outside (in a separate building), and the mass in the basement of the house. In this case, maybe a rocket is not the right path to follow?

What I want to heat is the house, hot water, and a planned greenhouse. The greenhouse will come 6m from the main house. I'm thinking that if I place the "heaterhouse" between those two, it could heat both the house and the greenhouse? Maybe the exhaust tubing can go through the greenhouse, while circulating water can heat the hot water and the mass in the basement of the house? The downside is that this requires a pump. Another potential downside is that the heaterhouse will get extremely hot, while just a fraction of the heat reaches the mass in the basement. Is there a way to transfer most of the heat to the water? Is it just a matter of how fast the water circulates and the number turns the pipes goes around the heater?

Is this all just a stupid idea?

The mass in the house I think will only be good for sitting, since the barrel gives your first heat, the mass is more of a conduction heat. I've seen water heated with wood stoves via radiator system, but with RMH is still iffy, haven't seen a proper system, plus they only burn for a short time. Green houses they work well, but to do all 3 would take allot of tinkering. I think the only way is to see what a RMH does in person if you can to see the full output. I never say never, but I don't think it will work. But hell, been wrong before!

Hi Peter,  It most certainly is not a stupid idea as sometimes innovation can be born from them, however..... You sure have taken on a lot of things all rolled into one package where there are plenty of factors involved. I certainly don't want to sway you from your dream idea, but also want you to be happy with having something that works real good rather than 4 things that don't work so well.
Would it be possible to break your system up into manageable chunks and make future additions?
Also, what your describing may be more along the lines of an outdoor wood furnace. Its a certified heater, it could be channeled to your house and greenhouse and it heats water for your domestic needs. Something to consider.

An outdoor wood furnace is an option. It's expensive though. And while living in a place where weather doesn't cooperate in regards to keeping wood dry during transport. Hence it's necessary to have a large firewood storage in the same building as the heater. (That way the heater also helps drying the firewood.)

What I really want is a DIY outdoor furnace, clean burning with firewood storage.

Heating the greenhouse, I'm sure the RMH will do fine. It's even possible to build the heater house next to the greenhouse so that the barrel gets inside the greenhouse. The challenge will be to get most of the heat into the mass under the house - that's where most of the energy is needed.

I'm thinking of various ways to achieve that - getting more energy into the circulating water than into the room where the heater is. One way would be to cover the barrel within a coil og waterpipes. (Putting the pipes inside the barrel I think will be too hot for the piping.) Then I could put isolation outside the coil. But then the barrel probably will be overheated. One way to deal with that problem could be to NOT use a metal barrel, but rather build a "barrel" of firebricks. Then make a coil of piping around and over this "brickbarrel", and lots of isolation outside this. This may introduce another issue - In a regular RMH he barrel has a cooling effect on the exhaust. This effect may be crucial to the airflow through the burn chamber. How can that be solved? Maybe by using a metal barrel without top at the bottom and extend with a "brickbarrel" on top of that?

Does anyone have experience with isolating the barrel of a RMH? Or stacking two barrels on top of each other? How did this affect the heater?

Safety is a big concern when dealing with heating water in a closed loop system. Here is a video showing a safe rocket water heater as an example to consider.

There has been much discussion on greenhouse RMH's on this forum which could also give you some insights. A quick search should bring up lots of info.

Here is an example of a batch box utilizing a double barrel system: Double barrel

Peter B. Onde wrote:I'd like to have a batchbox RMH. But I'm afraid that something will fail someday. So is the insurance company - if the house burns down as a result of not using a certified fireplace, they will not cover.

Ironically a properly made batch box is probably safer then a standard wood stove. There is no creosote to cause a chimney fire and the outer surface of the heater is typically cooler.

Peter B. Onde wrote:An outdoor wood furnace is an option. It's expensive though. And while living in a place where weather doesn't cooperate in regards to keeping wood dry during transport. Hence it's necessary to have a large firewood storage in the same building as the heater. (That way the heater also helps drying the firewood.)

What I really want is a DIY outdoor furnace, clean burning with firewood storage.

Heating the greenhouse, I'm sure the RMH will do fine. It's even possible to build the heater house next to the greenhouse so that the barrel gets inside the greenhouse. The challenge will be to get most of the heat into the mass under the house - that's where most of the energy is needed.

I'm thinking of various ways to achieve that - getting more energy into the circulating water than into the room where the heater is. One way would be to cover the barrel within a coil og waterpipes. (Putting the pipes inside the barrel I think will be too hot for the piping.) Then I could put isolation outside the coil. But then the barrel probably will be overheated. One way to deal with that problem could be to NOT use a metal barrel, but rather build a "barrel" of firebricks. Then make a coil of piping around and over this "brickbarrel", and lots of isolation outside this. This may introduce another issue - In a regular RMH he barrel has a cooling effect on the exhaust. This effect may be crucial to the airflow through the burn chamber. How can that be solved? Maybe by using a metal barrel without top at the bottom and extend with a "brickbarrel" on top of that?

Does anyone have experience with isolating the barrel of a RMH? Or stacking two barrels on top of each other? How did this affect the heater?

Are you willing to go outside and feed the fire every 15 minutes? If not then forget a RMH. Even a batch is going to get old going out and tending the fire every hour or so. Thats why large wood capacity boilers are so popular for outside heaters. If your heating a greenhouse and a home in an area with cold winters, you would need to do lots of burns with a batch or RMH.

Heating water with a RMH or Batch is not very effective since you are also heating a mass and need a good draft to run the stove. If you set it up to heat any decent amount of water, your draft is dead. Your only option to do both heat mass and water is to run a blower on the exhaust. You would not need a chimney and could use PVC exhaust.

Heating the soil in your greenhouse could be done with your warm water circulated through some pipe barried close to the surface. Can you put a heater in your greenhouse?

Check this out;
http://donkey32.proboards.com/thread/3552/el-tornado-experimental-build-thread

You and I are in the same boat Peter.
I too want a cheap DIY outdoor woodboiler,  for the very same reasons.
I agree with those words suggest heating a solid mass and a moveable mass(water) at the same time is probably self defeating.
My idea has been to use a rocket stove to boil water into steam ,move the steam into the house, and condense it back into water.
From there,I could run a line from our storage tank(s) to a coil in the return air duct and back,  forming a thermal siphon loop.

The need to feed the stove and where exactly to build it have stalled my process, but I have thought of ways to build a lot of the system cheaply.

The boiling vessel could be built of stainless steel mixing bowls,  stock pots,steam table pans and/or sinks.
Bathroom exhaust fans could push the steam through aluminum down spout  to the condensing tank(s) which would be made of derelict water heaters.
Water could be pumped back to the rocket stove to be  re-evaporated, or retained for household use.

In the greenhouse I might blow the steam into perforated pipe burried in the soil of the greenhouse floor or raised beds.

Ideally the greenhouse would be as close to the house as legally  possible, and the rocket stove would be located in it.

Gary:
Safety is not a big concern when heating water in a closed loop system, if done properly. Most new houses here has closed loop water heater. You need an expantion tank of propper size at the highest point of the loop. And you need one or two blow out valves.

RMH for greenhouse is something lots of people do. There are lots of experiences to learn from. I don't see that as an major challenge.

What IS a challenge will be to move away from the central principal of a RMH where a metal barrel is heating the room where the heater is located. The process to transfer most of the heat to the inhouse mass is the challenge here.

Thanks for linking to the stacked barrel design. I'll read up on that.


Mike:
The insurance company does not care what is safer or not. All they care about is the certification of the fireplace.

I'm not willing to go outside every 15 minutes. Thats why I'm looking for a batchbox design. (Even better would be an autofeeder.) With a large enough batchbox I'm hoping to fill it up a couple of times each day, (except for the coldest days) and let the mass do the heating of the house between each fill up.

I'm hoping that there is a balance for which the heater heats the water, without loosing the draft. If exhaust temperature gets below 80C, it won't contribute much to heating the water. Hence there will be some heat to make the draft. I'm thinking that if water pump is controlled based on water temperature (aiming for 90-100C), and there are two coils around the heat riser, with a valve controlling if water should flow through both coils or just the upper one depending on exhaust temperature, the system should be both efficient and ensure propper draft. That is one of the things I'm hoping a layer of firebricks between the heat riser and the coil of waterpipes will help with. I'm thinking the rest heat from heating the water will go to the green house. I'm hoping for one big heater rather than two (one for the house, one for the greenhouse).

William:
Steam is scary! I see your idea, but I think it's important to make the water circulate so fast that it won't turn into steam - temperature dependent waterpump. Efficiency using steam would be a lot better though. I'm thinking of using sand as the indoor storage mass. Steam would make it posible to reduce the size of the storage, while storing the same amount of energy. But I don't want to take the risk of using steam. I want to keep the water near boiling, And if it boils, let the pressure out.

I will not have the feeder opening in the greenhouse. I've seen RMH's that has been working perfectly for a long time suddenly smoke back. To minimize the damage of such event, I want the feed to be in a separate building. But I can have that building very close to the greenhouse so that the heat riser can go inside the greenhouse.

In my case there is no options for where to build the greenhouse, unless I accept the floor to be a 30+ degree slope. It has to go where ground is flat, 6m from the house, 2-3m above the mass in the basement of the house. The heater has to either go between these buildings or around the corner of the house, leaving it 3m from the house, 6m from the greenhouse, and 1.5m below the mass in the basement. Having the heater placed low may be an advantage when moving heat into the mass.

Considering that the heater has to be separate from the house, I would make it a masonry bell inside the greenhouse, with piping pumped to the house. This will at least make all of the heat do something useful instead of being wasted from the surface of a separate boiler house. You could put wood storage at the near end of the greenhouse enclosure for wood drying (separating the atmosphere from the humid greenhouse). The safest way to heat water is to have a large unpressurized tank and pump heated water from that (or from a coil submerged in the tank) to your house mass. Water tanks (unpressurized beyond any gravity head) in the house would let you store heat directly instead of suffering yet another conversion loss. Cool water from the bottom of the house tank would go back to the heater bell tank, and a toilet tank type of float valve would keep the tank level up.

An 8" or 10" batch box would give massive amounts of heat from a single batch, and a thick massive bell and corresponding quantity of house thermal storage would let heat be pumped to the house for many hours after a burn.

I would put in a covered/sheltered walkway from the greenhouse/heater house to as close to the house as the insurance company will allow.

I get your fear of steam,well high pressure steam anyway.
A challenge I kept bumping up against was finding a pipe material that could survive boiling or near boiling hot water,  but not cost an arm and a leg.
The distance to house plus anything uses in a heat exchanger coil  can add up.
The other challenge was the volume of water needed capture/move/hold the heat of a single batchbox firing.
It's a large amount if you use liquid water.
Both of these things drove me towards low pressure steam.
But these ideas are untested, and driven by my own circumstances.


There might be a reason beyond smokeback that you don't want the heater in the greenhouse, but otherwise, Glens batch box in the greenhouse makes a lot of sense.
A batchbox has a door to prevent smokeback,and it produces more BTUs than a J rocket.
You could still put the loading0 door outside.
The heated water could drain towards the house.
The pump could be placed at the coolest point of the houses storage tank,  where it would have direct access to power,  and a low amount of exposure to heat.
The heat of the return water can be well below the limits of PEX,  allowing some savings on pipe.
Derelict water heaters can be daisy chained together to become the basement heat storage tanks.
They come insulated,  but if you want them to radiate heat,  you can strip that off.
If you build a box around them, you could fill that with sand, for even more mass.

I use warm water and it does the job. Steam is awesome but that’s some serious stuff. They were massively heavy iron and fitted by steamfitters for reasons. Add me to the list of people who want a easy to use pseudo boiler in a greenhouse either attached or near the home.
I’d like to build a centralized DIY pseudo boiler in the center of a wagon wheel so school buses, gypsy wagons, RVs, etc could circle it and hang a hot water radiator in the window to heat. A big communal greenhouse would be in the center. Imagine if the dominant paradigm had been something like this. Oh, but they would not make loads of money and make people dependents with self sufficient systems such as this.

I was just looking into PEX pipe again, to remind myself of the specs.
Its so cheap and easy to use, I am drawn back to it again and again.
I'm seeing 200 F at 80 PSI.
Not too shabby.
I don't know how to calculate the PSI created by a pump, but that might only be on the "cold" leg anyway.
Assuming 12 degrees of loss, before the water meets the PEX, it should work fine.
I'm not sure that's a safe assumption.
What do y'all think?

I have a few derelict water heaters.
If I could immerse a bare tank from a water heater into a larger tank, it could act as a heat exchanger.
The surface area to volume might would suck.
At least one of the tanks I have came from a gas powered heater.
It has a vent for exhaust gasses running through the center of it, that would improve the surface area to volume a little.
Most of the water heater tanks I have are smaller in diameter than a 55 gallon drum.
They are usually longer than a 55 gallon drum is tall , but cutting one down is easy.
Fabricating a tight fitting, insulated , but not pressure holding lid , should be easy as well.
If a tank-as-heat-exchanger thing works, it might overcome one of the biggest costs I associated with DIY outdoor wood boilers, the copper heat exchanger.
I wonder if adding gravel to the tank would improve the surface area to volume ratio, displacing the water and make the water "dwell" longer.