Rocket Mass Heater outside of home for inhome purposes

Hello
I live in Denver in a home that I would really like to use the RMH. I am told that insurances wouldn't cover it with RMH

Is it possible to build the unit outside (and I have enough space) and guide/siphon the heat into the home?

Thanks for your help

Hi Ram;
When your dealing with uninformed insurance people it can be tough to legally use a RMH.
Only thought I have is to build a room outdoors containing the rmh and insulated vents going to the house. Here's the problem with that... A) it will not work very well and ....

B) Enter the innocent but uninformed insurance person...  (A Favorite saying)  YOU CAN"T DO THAT !!! its too close to your home, my gosh what if this funky non certified home built hippy contraption caught on fire ?  Your home would burn down and MOST IMPORTANT...the  insurance company will not pay (The Most favorite saying)

Some people (not recommending this mind you) But some people just build one anyway...  (bad people) who are rule breakers ... who question authority (how dare they!!!)

As a responsible Permies person you should never think that way...  

Have a great day !

Good advice.

I have to convince my family too and hence these "jumping these hoops"

How far have people siphoned heat from location of heat generation to the location of heat use. Is the Mass normally kept heat generation area or at the home (where its consumed)?

thomas rubino wrote:Hi Ram;
When your dealing with uninformed insurance people it can be tough to legally use a RMH.
Only thought I have is to build a room outdoors containing the rmh and insulated vents going to the house. Here's the problem with that... A) it will not work very well and ....

B) Enter the innocent but uninformed insurance person...  (A Favorite saying)  YOU CAN"T DO THAT !!! its too close to your home, my gosh what if this funky non certified home built hippy contraption caught on fire ?  Your home would burn down and MOST IMPORTANT...the  insurance company will not pay (The Most favorite saying)

Some people (not recommending this mind you) But some people just build one anyway...  (bad people) who are rule breakers ... who question authority (how dare they!!!)

As a responsible Permies person you should never think that way...  

Have a great day !

I think you are on the right track.  Also in Denver, we can build a 10x12 shed without a permit (may be off on the size a small amount).  So how about a super insulated shed 10 or 15ft from the house set up as a sort of RMH heated sauna.  There are insulated flexible vent hoses often used in indoor growing here that could be buried or perhaps used above ground and sort of temporary connecting the sauna to the house.  The RMH itself wouldn't need any modifications I don't think.  We'd probably want to sauna to get uncomfortably hot to deal with the losses through the insulated lines but no where near fire danger.  I've been thinking about this same option as OP but using a heat exchanger and I like your building idea way better.  I think I'd want two lines, one for hot air and one return.  A blower of some sort on the hot air line inside should be enough.  I guess we could add a thermostat to the blower and treat our sauna as a heat battery.  A thermostat near the blower/vent would warn us when the RMH needs fired back up.  If we want to spend some $$$ we could make the sauna quite fire resistant with certain materials but I'm not sure I see the need.

I've also considered just blowing hot air into the crawlspace I have since it's already insulated around the perimeter.

Buster,
Thats good.
Can we talk offline? I dont if theres a way to send private message to exchange phone numbers

Guys I'm sure it can be done but...  in that scenario you would want to build a batch box rmh over a J tube. AND it will be badly inefficient.
A rmh mass should be in the room with you to enjoy its warmth.  If you are trying to push / pull that hot air thru pipes to the house, the volume loss in line size ,plus the line loss of heat.. it would hardly be worth it. Super hot in your sauna and luke warm air coming in the house. Plus an hourly trip out to the rmh to refill it... really a lot of work for a luke warm return.

Now there is a style of wood burner, known as a Hasa. With a large firebox surrounded by mass with large insulated pipes underground coming indoors. Built away from the house it is designed to be burned for long period's at a time.  Uses fans to move the hot air. And insurance people are usually OK with them.

thomas rubino wrote:Guys I'm sure it can be done but...  in that scenario you would want to build a batch box rmh over a J tube. AND it will be badly inefficient.
A rmh mass should be in the room with you to enjoy its warmth.  If you are trying to push / pull that hot air thru pipes to the house, the volume loss in line size ,plus the line loss of heat.. it would hardly be worth it. Super hot in your sauna and luke warm air coming in the house. Plus an hourly trip out to the rmh to refill it... really a lot of work for a luke warm return.

Now there is a style of wood burner, known as a Hasa. With a large firebox surrounded by mass with large insulated pipes underground coming indoors. Built away from the house it is designed to be burned for long period's at a time.  Uses fans to move the hot air. And insurance people are usually OK with them.

There are certainly losses to minimize, ohm's law doesn't sleep but I think it's an interesting enough idea to try and quantify the losses.  To start I modeled a few different ducts with and without insulation.  One way to keep losses low in the duct is to move the air through it quickly.  I have a 400 cfm, 150 watt, 6" blower and plugging that in at 150 CFM to account for some drag I could see a 5 degree F drop across a 15' length, 120 to 115  (used 0 deg outside temp).  That's with an inch of foam insulation.  I'm ok with that.  With no R value it would be a 20 deg drop, badly inefficient for sure.  Good call on the batch box over j tube, much easier to operate for an outdoor attempt.  I guess I'd use this sort of setup as much as possible with my existing furnace as a backup, maintain a low minimum temp overnight, etc.  I didn't model losses through the sauna shed since that's so simple and really comes down to the total surface area, temp delta inside/outside and how much insulation one wants to buy or source second hand.  I also agree that losing the warm mass indoors is a big one for the overall comfort a typical RMH provides.  I guess a second indoor mass could be added which shouldn't be a problem for insurance.  With proper planning one should be able to determine at least the amount of heat expected to be lost from the structure and duct before starting.  I believe it could be designed in a fashion that is far more efficient than an inside wood burning stove since we start out so far ahead with the rocket heater efficiency.  To be fair we'd need to add the blowers draw of 115 watts to this designs losses, though that's only when running.  I'm not sure that badly inefficient is a given, just somewhat less efficient depending on design.  I appreciate your ideas and hope you'll mention other problems with this sort of setup.

Ram , I'll send a PM

Hey Ram;  Have you considered a masonry stove ?   Generally if it is connected to an acceptable chimney , insurance company's will accept one.
Your family might be more inclined to accept it as well.
The insurance company will want it built by a professional.
It is possible to do yourself.... of course a "good person" like you would tell that to the insurance company...

I find it interesting that masonry heaters are more or less universally accepted by insurance plans, but call it something else, like a "Rocket Mass Heater", and they won't cover it.

Hi Jason;   Masonry heaters have been around for longer than the insurance company has been...   Kinda hard to deny something that's been working for close to a thousand years. (I don't really know how long)
Rocket mass heaters were invented (I think) in the 1970's. The insurance company monopoly was well established by then. Set in their ways.  A new fangled hippy stove built for almost free out of mud !!!
choke choke bluster... YOU  CAN'T DO THAT.... for sure it will burn the house down !!!  Ha Ha and THE INSURANCE COMPANY WON'T PAY !! I heard that somewhere recently...

It can/has been done, but resistance to allow change is strong with stodgy old insurance people.

If you're thinking of transporting the heat from an outbuilding, then you should consider using water as the transport medium. If the outbuilding is well insulated, then you could even put a storage tank out there to hold onto the heat from each firing until the house needs it.

I have plotted similar schemes for the same reasons.
Combining the clean burn of the rocket stove with the infrastructure of the outdoor wood burning  boiler is the goal.
The BTUs that a batch box can produce in one burn is one limiting factor.
The BTU/gallon of 212 degree  water is another.
Beyond that, the phase change from water to steam takes a huge additional amount of BTU's,which could be very useful.

I'm somewhat convinced that  boiling off the water outside and condensing it inside is the only way to move a suffient  amount of BTU's within the burn time of a batch box.


A related,but underdeveloped technology to a rocket mass heater would be a charcoal producing stove mass heater.
A charcoal producing  stove produces charcoal as it burns the feed stock.
They are on the whole,clean burning,  and can be extremely long burning.
Capturing the heat of that burn in a mass has been often proposed but seldom implemented.
I see the long burn times of these charcoal producing stoves as a clean answer to dampered,smoulder fires.
The charcoal produced has many potentially uses, as soil amendment(bio-char), homestead income(willow charcoal  for artists, charcoal for smiths and pitmasters), and fuel for internal combustion(vehical gasification).