Single loop radiant floor RMH questions

Hi, I have a few questions about a RMH-heated radiant floor system. I found in another thread that Ernie Wisner had been experimenting with one, but I couldn't find anything about how that had turned out. So, Ernie, I'd love your input on this, if you're available.

I'm wanting to install an RMH in a trailer home (yes, I'm beefing up the foundation in the location where I'm going to build it). The best location is at one end of the trailer, so I quickly have a problem of distributing heat to the other end of the trailer. I don't like the idea of running a fan in the hall, like I've seen done in other wood fire-heated homes, so I thought I'd install a radiant heat system in the floor, covered by 1" of cob, and harvest some of the heat from the exhaust of the RMH (Ernie discouraged harvesting it from the heat riser). I only need a single loop (shouldn't be more the 250' long) system. My current plan is to install a holding tank with a decent amount of head space and a pressure relief valve along with a pump on the cold side of the loop.

So, here are my questions:

1. Does anyone see any major problems with the basic system I'm describing? For instance, should I shorten the length of my exhaust since I'm harvesting heat from it? Is there any reason a simple, single loop system is not a good idea?

2. How many times should I coil my copper tubing around the exhaust (Ernie mentioned elsewhere that the first 5' would be the best place to coil it), so that A.) it gets warm enough, without B.) getting so hot that it creates comfort issues or pressure problems (I don't want my pressure relief valve being triggered all the time)?

N. Taylor: Welcome to Permies and a big WELCOME to the 'Rocket Stoves Forum Threads'. While we are waiting for Ernie W. a few thoughts on your future build.

So that we can both read off of the same page, have you been to Rocketstoves.com to download your Pdf copy $15.oo U.S. of Evans' and Jackson's
great book "Rocket Mass Heaters"? there is no other source of rocket stove Information available in any language! - (and I don't make a dime ! )

With most of the utilities going under the trailer, heating duct works, electrical, and water you have a project that many would fear to tackle, but you've got a plan
so you have probably covered that already!

I would strongly suggest that you use a commercial grade boiler Pressure and Temperature relief valve, and also make sure that a pressure drop in your water
system would automatically add makeup water as close to the area where your copper pipe is wrapped around your horizontal exhaust gases stovepipe . I'm sure
Ernie will weigh in on this !

Not knowing anything about your trailer and its size/age, and location, sizing your rocket stove would be a W.A.H. Guess. I did want to make sure you were prepared
for the lifestyle required of the one who lives with a rocket stove, The Dragon that lives in your Rocket Stove needs frequent feedings of small wood as often as every
1/2 hr until the Burn Tunnel has stored enough heat to cause wood fed into the Feed Tube to burst into a primary flame within seconds of its application ! Thereafter,
you may be able to enjoy feeding it every hour taking time to subtly adjust the airflow to balance the mass of the new wood. This system works best when the Rocket
Stove and its Feed Tube are no more than an Arms length away! If your favorite hang out spot is not close to your Rocket, it will quickly turn into a chore to get up to
walk down to the far end of the Trailer. In other words the Rocket stove is not a 'load it and leave it' alone system! It is designed for a home that has someone there
at least 6-8 hrs to feed their dragon in order to get 20-25 hrs of stored heat! Not following this simple rule will find you returning home to a cold house !

You may have considered this and Are prepared for this lifestyle change, and/or have a partener who is willing to take on the challenge, but it can not be said enough !
Thanks for letting me deliver this message in your forum/thread !

For the good of the Craft! Be safe, keep warm PYRO Logically Big AL As always any questions comments are encouraged and appreciated !

Why not just run the exhaust flue under the house, and straight out the other end of the foundation? Wrap the first 20 feet of the flue in cob, or some other light insulation/heat barrier to slow the heat loss on the high temp end, then staple a vapor barrier under the flue & such. If it is going to be inside of a compustible channel, this might not work, or might require some heat shielding for some stretch of the run. You will have one warm stretch of floor.

N. Taylor : Creighton's Idea may work very well for you, but it's hard to tell without a general layout of the trailer and the amount of room/headroom under it,
and does it still have its delivery Axles and rims under there! Also and this is important if you want to continue to use the Trailers furnace for a back-up, Your
primary air supply for your trailer comes from underneath, we can not seal up the bottom of the trailer without supplying your trailer furnace with its own air from
outside !

Generally speaking, I think that probably a 1'' cap of cob over the top of your radiant floor tubing is not going to be thick enough, We have an excellent forum
space dedicated to all things Cob where you should be able to get an answer to that question !

Keep the questions coming someone is here usually 24-7, and you should get an answer ,or twenty, within a day !

For the good of the Craft ! be safe, keep warm, PYRO Logically Big AL ! - All comments are accepted and welcome !

I would like to revise my suggestion(s) a bit.

I would say that you should insulate the flue through the floor and for the first couple of feet further until you can run it inside of another sheetmetal duct a bit larger. It would not really need to be insulated, as any heat loss would benefit your crawlspace to keep it dry anyway. Run the flue straight out the far end of the foundation, but not the ductwork. Pipe a makeup air line into the furnace from that ductwork, and another from the ductwork near the farther end of the ductwork out the side of the foundation. Make sure that the make up air pipe is not near the flue exit. If you are brave, you could instead make the ductwork part of your return air of your furnace instead; but you would have to make certain that your flue is very well sealed, check it annually, and install carbon monoxide detectors in your home. You'd be wise to buy carbon monoxide detectors anyway. If you did run the flue through the return air, you'd also need a heat switch on the flue under the house near the hot end to tell the furnace fan to turn on even when the thermostat was not calling for heat. A properly installed and maintained single walled stovepipe should not leak, but I'd be certain to coat the installed flue with a few layers of high-heat paint. Particularly near the joints. Your useful heat should be pretty high, even without useing the ductwork as a return air. The ductwork would function both at a heat exchanger, making sure any make up air for your furnace (and your water heater! And your rocket mass heater if you do it right!) is pre-heated, but also as a heat sheild and mild insulation for the space under your house. You'd effectively be using everything under your house as heat mass, and heating the sub-floor via both convection and direct infrared radiation, but not enough to create a hotspot. If this scares you, then just hang the flue, uninsulated, 18 inches from the bottom of the subfloor, and it will directly heat most of the subfloor via IR radiation. Your crawlspace will be very dry. Laying down mylar sheets held down by bricks on the dirt below the flue would also reflect IR back up and spread out the heat. A third possibility is to run the flue, somewhat insulated, to a "heat bell" at the other end of the house, and then out of the foundation. Another 55 gallon drum at the far end of the house, with the flue piped up into the bottom and then another back out of it and out of the foundation, should work well for this. The second drum will not be nearly as warm as the first, but it will get warm to the touch, and you would be heating your home from both ends.

Water will condense inside the horizontal part of your flue. Perhaps a drip leg with a valve to empty it out each summer, if you use the "heat bell" or just run the flue slightly downhill (use a plumber's level) towards the exit otherwise.

Guys, check for hypocaust!

That would work excellent also, but then the entire crawlspace would be the flue, and he would need to take care to airflush the space anytime he needed to get into it in order to fix something. That would definately be the cheapest method of heating the entire subfloor, but some degree of insulation for the crawlspace itself would be required.

As a bonus, the low oxygen environment would kill all of the summer spiders that like to live in crawlspaces. Mice too.

Satamax A. : Do we have the location of a currently working hypocaust ? For the good of the Craft! be safe, keep warm Pyro Al

allen lumley wrote:Satamax A. : Do we have the location of a currently working hypocaust ? For the good of the Craft! be safe, keep warm Pyro Al

Don't know any. Thought, someone stated that there's some in use, somewhere in asia. Can't remember if the discussion was here or at donkey's.

Thanks for the input, guys.

Running the flu under the trailer is a great idea, except... there is insulation between the joists, so I'd basically JUST be heating the crawl space. I love critters, but I'm not THAT concerned about their well-being (esp. since I'd rather they weren't under my trailer in the first place).

Oh, and, yes, I do have that book, Allen.

I also purchased plans from the Wisners for the 8" bench system. I'm going to be making some minor adjustments to the bench itself (nothing involving flu length), but that should give you an idea what I'm planning to work with.

allen lumley wrote:make sure that a pressure drop in your water
system would automatically add makeup water as close to the area where your copper pipe is wrapped around your horizontal exhaust gases stovepipe

Not following. How would I accomplish this?

N. Taylor wrote:Thanks for the input, guys.

Running the flu under the trailer is a great idea, except... there is insulation between the joists, so I'd basically JUST be heating the crawl space. I love critters, but I'm not THAT concerned about their well-being (esp. since I'd rather they weren't under my trailer in the first place).

Then insulate the crawlspace stovepipe, and run it up into an uninsulated heat bell at 2/3 towards the other end of the home, and then out the far end of the foundation. As long as it's not too far to push the air, this will give you another heat distribution point towards the far end of your home. I'd estimate that the heat bell should produce another 20 to 25% of the btu's that the heat riser produces. You could still do the hydronic heat as well, by running copper tubing around your underfloor flue on the inside of the insulation, but that would neither be necessary nor cheap. At least if you do run hydronic heat coils, and the overpressure value should fail, your resulting boom-squish event would be largely contained into a non-occupied space; greatly reducing the risk of human harm.

The heat bell might only need one pipe up through the floor from the underfloor flue. the theory is that since hot air is inclined to rise, natural convection will compell some hot gases to rise up into the heat bell, cool, and then fall back down as more hot air comes to take it's place. Not the most efficient way to do it, but certainly low maintaince. Even just a couple sections of single walled stovepipe with a sealed cap at the top would be enough for a couple Kbtu's at the far end of the home.

N. Taylor : The type of valve you want functions similarly to a Water Temperature mixing valve, only responding to Pressure rather than Temperature ! I will think of its
technical name 30 seconds after i post this !

It is nice to have Evan's and Jackson's Book to refer to! Please note the plans to 'off set' the barrel ( page 24 w a good picture ) from the Heat Riser Creating a warm side
and a hotter side allowing you to protect your exposures !

The barrels off set should be directly over the generous cavity ( with an ash pit ) that the hot exhaust gases flow down through from the bottom of the barrel, making a
sweeping right angle turn to be funneled horizontally straight out through a clean out 'T' and into the Thermal Mass's stove pipe

I believe that E & E Wisner recommend the 55gal drum With a removable end held on with a clamping band. This makes inspection and cleaning ,and clean up after, much
easier. If you have any trouble understanding how to burn off/out the barrel let me Know !

Have you considered the path that you will take carrying wood to your stove from out doors, I worked on a build that had to be totally reworked be cause the Owners had
given it no thought at all!!

For the good of the Craft! Be safe, Keep warm! PYRO Logically Big AL. - As always all comments are encouraged and welcome ! A.L.

N. Taylor : -have you heard the one about '' A camel, is a horse designed by a committee'' Best of luck !

For the Good of the Craft, be safe, keep warm! PYRO Logically Big AL, As always, all comments are solicited and welcome A.L.