Retrofit your wood stove

It should be possible to have a little fun with firebrick, pipe, steel, etc. to re-fit an existing wood stove after seeing those amazing rocket stoves. Also, ideas to retro-fit a fireplace with firebrick and pipe to also improve the efficiency.

My in-laws have a nice wood stove which is a simple design that is long (front to back) with the rear top of the stove angled up, providing additional room to burn.  Uses wood up to 36 inches long or so.  But there's really nothing very efficient about it.  I've wondered about dividing the box into two sections by placing a steel shelf inside, placing firebrick on top of that, to create a longer burn tunnel. Has anyone tried something like this?

I have played around with our wood stoves over the years. I best thing that I have done to increase their efficiency is to add heat exchangers to the exhaust. However, I did find that if the heat exchanger is too big it sucks too much heat out of the stove pipe and caused problems with build up in the chimneys. With on heat exchanger we had a "chimney fire" in the heat exchanger, but not the chimney. I still use a heat exchanger out in my shop, but pulled the one off the stove in our house for safety. I think the beauty of the rocket mass heaters is the storage of the mass.
kent

I would think that simply adding mass around the outside of the heater should help for starters.  My in-laws live too far away for me to tinker with it,  but I'll be trying a couple of things if/when I can be there long enough.

whisper, you must have a good relationship with your inlaws. rose.

Oh, I DO.  They're WAY up there, and I'm WAY down here   Seriously though, I do.  Good people.  Matter of fact, my mom-in-laws name, is....Rose!

You don't want to mess with a chimney in your house - no way, no how!  In fact, never burn anything other than newspaper or wood in a woodstove, as regular paper WILL cause a chimney fire (it turns into charred paper and floats up, gets caught and starts a fire).  We had a chimney fire last year after my mother burned a bunch of old bank statements in the stove.  Not fun - the roof started melting and the bedroom above the fireplace filled with smoke. 

However, I have considered getting one of those cheapy wood stoves and converting it to an outdoor rocket stove.

The best thing you can do to make a regular wood stove more efficient is to build a thermal-mass wall around it (and add a grate inside to keep air flowing beneath the logs).  If the floor is an on-grade slab it should be no problem, but if it is above a basement or another floor you will have to reinforce the joists below to carry the weight.  A 4 ft. high 8" thick brick wall on each side should absorb a lot of the heat and keep it in the house for a good 12-24 hours after the fire goes out.  We have an efficient Jotul insert inside an old brick fireplace that is 8” at the interior face, much thicker outside, and the bricks inside are still warm 24 hours after the stove itself is cool enough to put bare hands inside.

IME; yes you can retrofit a wood stove. Its just lots of work. the insulated heat riser is where the stove pipe leaves the stove and the barrel is mounted over that. the manifold and such will have to be reasonable (however i dont think it would hurt it to go all the way back down).  in some ways the height of the whole thing could be controlled by removing the legs of the stove and setting it down on a couple rows of bricks. the trick will be to cob as many of the air controls as you can so folks dont choke the fire down till it wont work right.  you will have to experiment on a test system to find the right configuration but it can and has been done. 

We have a simple cast iron box stove which we surrounded with masonry. We burn it on high. The heat is stored in the masonry. There are air exchangers in the wall behind the stove built into the masonry. This works very well. Someday I would like to build something better and more complex but until then it is effective. More is fun but not necessary as we already burn very little wood to heat our house.

Cheers

-Walter
Sugar Mountain Farm
in the mountains of Vermont

yep Walter it works for heat.
however a RMH is supposed to put out little to no smoke. ours puts out CO2 and steam for most of the burn. about the first 6 min it puts out a little smoke. this equates to me bringing in a single arm load of wood a week (it seldom gets below zero here so i would assume you might bring in two or three armload's of wood). All in all i burn a quarter cord of wood to my folks next doors 3 cords. typical here is 5 cord a winter.  Each to there own.

The original post sounds like something I've seen before, here's a link.

http://geopathfinder.com/9597.html

Cheers

Ernie Wisner wrote:All in all i burn a quarter cord of wood to my folks next doors 3 cords. typical here is 5 cord a winter.

We burn a little less than 0.75 cord of wood a year. This is our heat source. It puts out almost no smoke. Same principles as the rocket stove with the way we set it up. The mass was the key to capturing the quick burn.

Thanks for the ideas, everyone.  I just got back from my inlaws, and I looked at their stove.  Couldn't find my camera!  And I missed something that you just pointed out, that the RMH's burn full-blast, with no in-between temps-shutting down the dampers on the stove.  I really like the added masonry idea, and adding a grate to the bottom.  I also went and looked at new stoves. The ones they had also did not appear to be adjustable like the old one.  Not enough time to check them all out.  In the long run, it might be more cost effective (and easier for them) to just replace the old one when considering bracing the floor for the weight and such.  We'll see!

Hi there, I've got a wood stove with a hydronic heat exchanger running through it that pre-heats all my house hold hot water. Thus greatly reducing the bills in the winter, or if you live were I do in the fall and early spring too. The stove also has a thermal mass chimney that stores and holds the heat. I'll post some pictures and be happy to answer any questions that arise.

Here's a pic I took on my recent trip home.  Looks very much like the one with the heat exchanger! It's a good old stove, been there for many, many years.

leecha wrote:
Hi there, I've got a wood stove with a hydronic heat exchanger running through it that pre-heats all my house hold hot water. Thus greatly reducing the bills in the winter, or if you live were I do in the fall and early spring too. The stove also has a thermal mass chimney that stores and holds the heat. I'll post some pictures and be happy to answer any questions that arise.

couple questions:

So, the chimney goes up through that cinderblock column, right? Is the metal of the chimney right up against the block, or is there filler in there as well?

I see two pipes going into the stove and then back through the wall - can you go into more detail about the heat exchanger, how water gets from point A to B, and how you deal with pressure building up in the system?

Some friends of mine were considering a similar approach with their woodstove; I'd appreciate hearing about your build process, what worked, what didn't, and what, if anything, you'd change or do differently.

thanks!

Hello I hope I can answer you. There is no filler the pipe goes right through the block and then stops just on the inside and is sealed with a flange.  The system works on normal household pressure, (in my case usually 50-60 psi) the flow first goes into the bottom of the holding tank, where it then passes through normal pressurization into the the bottom pipe of the heat exchange loop, then back into the top of the tank. Water is then passed onto the hot water tank from the top of the holding tank. From there on its regular plumbing. You should size the holding tank to fit you household demand. In thirty years of running I only had to recently replace the pressure relief valve on top of the holding tank, it got bunged up with corrosion and wouldn't shut properly. By the way the hot water tank is the original that I installed when I built the house in 1981. The heat exchanger is a passive loop, that reaches temperatures of around 200C. If I was to build this again and I would, I would use rheem's marathon thermal storage tank, for its none corrosive properties and R20 insulation.

Whisper,  I have a little experience with these things, and I can give two quick points of advice: 1st. the stove, lining the fire box with fire brick might be a good idea, a smaller fire box can be more efficient and the added brick is a thermal mass.  The trick with a smaller burn box is to use smaller diameter wood, which will burn hotter and faster.  If you are in the habit of throwing a big ol' chunk of larch on and "shutting her down for the night" this might not be for you.  As for retro fitting, the best thing you can do (if you don't have it already) is to install an external combustion air pipe to the bottom of your fire box, that way you are pulling air from outside rather than the warm air that is already in your house. 4 inch diameter flex pipe works great for this.
2nd. The fire place.  Without a picture I can't really tell you what to do.  Generally installing metal pipe up a chimney is a pain in the butt and doesn't do any thing for an open fire place, part of a good fire place design is the smoke shelf, which insures proper ventilation, putting a pipe in wont help this.  Depending on the shape of your fire box, you may be able to retro-fit with fire brick to turn it into a Rumford fireplace.  I will let you do your own research on Rumfords but they are super efficient, giving off more radiant heat and less exhaust than a typical fireplace.

Here's another link:
http://www.handprintpress.com/ovens/solstice-2010-bring-in-the-mud-into-the-house-that-is/

He calls it a hat.

Thanks, that was very interesting about the "hat".

Whisper wrote:
Thanks, that was very interesting about the "hat".

There are often different ways of doing the same kinds of things. Both RMHs and masonry stoves try to do the same thing... burn fast and clean, but use mass to store the heat for later and keep the room from being to hot. In general, the two worlds don't interact too much. I find I learn more by following both worlds. I got that link from the MHA news letter (blog? whatever).

Some interesting reading! The links too!

I'll put in my 2 cents worth here:  I have a large stone wall (12+ tons of local granite rock - dry stacked) inside my house that most people call a fireplace... probably because it has a little thing on the bottom that burns wood.  But the reason i put it in has nothing to do with a fireplace.  I also have a copper coild for water heating, and a 8" vertical chimney that runs through the middle.

The thermal mass of the stone has 'dampened' the temperature swings inside the house by over 12F (cooler in summer, warmer in winter) without ever lighting up the fireplace!  I also positioned (part of the initial design) the fireplace in the center of the house and also allows winter (lo angle) sun to hit it for 6+ hours each winter toward the SW setting sun.... so it really is a Trombe wall.

I 'stoned-in' a small fire stove next to the fireplace which i keep fired up most of the time as a kinda slow burn... to heat water and cook... and also keeps the temp of the rock wall going at night or cloudy days.

If i had known about RMH's 10 years ago, when I designed this, I would've done the whole thing totally differently.  I'm still looking for ways to retrofit it, but it may just be beyond that... way too much stone I would have to move.

I am hopeful that some cool ideas will come from this forum, or my own playing around with various configurations of RMH's to retrofit my 'fireplace'.  What really give me pause tho, is the carbon monoxide potential of  enclosed RMHs.

I have an old cast iron pot belly wood stove. Do you think I could apply the principles of a pocket rocket to this? I was thinking of attaching a short pipe to the small opening and it would act as the feed tube and put a long pipe over the original chimney opening. Would that reduce the amount of smoke coming out?