My masonry stove heating hot water to 500 gal tank under basement slab -- pics

[mobile_bob]

water walls don't have water running through the cast iron, rather they have a number of steel pipes covered with the cast iron plates,
which basically become radiant heaters to transmit the heat of combustion to the coolant in the pipes

the goal i suppose was to keep the active flame off the pipes and the coolant in those pipes helped to cool those cast iron plates extending their useful life.

i have a few books with drawings, i will try to get a scan and post it
often times a picture truly is worth a thousand words

bob g

[mbryner]

hi crofter,

TPR valve is at the top of the loop, and it's a closed loop filled w/ distilled water.   If the pump fails and it blows off steam I'll have to get behind the fridge to access the pipes and refill.


Actually I was expecting a little more polarized reaction from this group about this whole setup.   The solar panel guys from an install bid thought I was crazy for sure.   They said it wouldn't work.   

[Crofter]

water walls don't have water running through the cast iron, rather they have a number of steel pipes covered with the cast iron plates,
which basically become radiant heaters to transmit the heat of combustion to the coolant in the pipes

the goal i suppose was to keep the active flame off the pipes and the coolant in those pipes helped to cool those cast iron plates extending their useful life.

i have a few books with drawings, i will try to get a scan and post it
often times a picture truly is worth a thousand words

bob g

OK, I had in mind the ribbed, flat, cast iron water vessels that were add ons to wood fired heaters; maybe "water back" or some such nickname. Any scheme is good that either protects the pipes or makes them accessible for easy service without a lot of dismantling when (not if) they leak or plug. I have made some money but never had any fun inside of any furnace. The refractory insulation of blast furnaces is chock full of cast copper or red brass chillers to protect the shell. After a few years of service you never saw such a sorry lot of weeping, steaming, corroded piping.

I heat my DHW with wood but unless you babysit it to control temperature you have to automate it and build failsafes.

What Marcus is doing with batch firing, lots of thermal mass, etc. gets rid of a lot of the problems of overshoot. That kind of fire is the least corrosive too. The other bugaboo of that firing was mentioned- thermal shock. Steady firing is much easier on the refractory brick.

[mobile_bob]

geesh, wouldn't it be a blast to win a mega lottery!

a guy could go absolutely crazy, designing and building all sorts of cool stuff.

btw, Marcus

i really like your place, it should provide a sense of accomplishment and security for many years to come.

beautifully done.

bob g

[Crofter]

hi crofter,

TPR valve is at the top of the loop, and it's a closed loop filled w/ distilled water.   If the pump fails and it blows off steam I'll have to get behind the fridge to access the pipes and refill.


Actually I was expecting a little more polarized reaction from this group about this whole setup.   The solar panel guys from an install bid thought I was crazy for sure.   They said it wouldn't work.   

Marcus can you slip your heat loop out by just undoing connections?  I see you have covered the scale buildup problems and temp. and pressure relief plus expansion. Nice looking soldering! 95/5?

I have a loop of 3/4 ss about 4' with three of that in the stove. I just have to take the unions off and it slips out the front door. I only have a 40 gallon tank. The piping is 3/4 flex tubing with all joins silver brazed. Pure thermosiphon but no isolation so with 100% untreated makeup water I will get some scaling.

You have near double the pickup area so you may be quite close to balance all your hot water usage. We are just two dirty old folks so we do not go through as much hot water as you will. I can bias the fire toward the coil or over to the other side of the box to regulate a bit. Haven't tripped the TPR valve yet but have made it nervous a few times.

I hope you make out well with the refractory. One of the most common errors is fitting too tight and the bricks crush themselves. Same error is done with clay chimney liners.  Problems can come later on as the spacing gets compacted and filled with glaze. At least the option is there to reline without dismantling the exterior. I think the yearly thing is by far the worst case scenario. You are definitely a technophiliac though, lol! I find I am reverting more and more to stone age technology as I get older. When you are younger you need more things to try your horns on.  Fabulous project!

[mbryner]

Marcus can you slip your heat loop out by just undoing connections?

Unfortunately, no.  On the other hand, it wouldn't be overly difficult to remove, but would require a bit of new mortar.   The connections in the back of the stove are done w/ unions instead of solder.  The heat loop is mortared through the back of the stove.

95/5?   I don't know.  It was just the regular drinking-water-safe solder at ACE hardware.   I am a total amateur at sweating pipes together:  just learned a few weeks ago.   About 2/3 of the joints you see in the pictures were done by the plumber, not me, so I can't take credit.   I did all the joints that interface w/ the underground tank, masonry stove, and associated valves.  At least they don't leak.       You'll notice parts of it I used CPVC because I was unsure of my solder skills initially.

The accepted practice is batch firing a masonry stove.   You do it with the dampers and flue wide open so it burns as hot and efficiently as possible.   What happens when I don't burn such a big batch, and burn small batches only a few hours apart?   Since the thermal cycling shock is the eventual downfall of the stove, would that help?   I've never used a masonry stove until now so it's a learning curve.

geesh, wouldn't it be a blast to win a mega lottery!

a guy could go absolutely crazy, designing and building all sorts of cool stuff.

exactly!   wooo hooo!

[sailawayrb]

Marcus,

Going from memory since at work during lunch hour...

The general practice for "running" masonry heaters as best I understood it from reading all the various core vendor's installation/owner manuals available on the Internet and from reading that masonry heater design book I previously referenced goes something like this:

1) Pick the right heater based on it's BTU output relative to the size of your home's heating requirements.  Perhaps use software like Energy 10 to figure this out.

2) Locate the heater in the center of your primary living area because of radiant heating.

3) Always use seasoned, very dry wood.  Masonry heater cores don't like moisture because it creates significant temp differences across the core that create significant thermal stress.

4) Break it in slowly by starting with very small fires (maybe 5-10 lbs) to slowly drive all the moisture out of the core over a period of several days.

5) Decide on either a 12 or 24 hour firing cycle.  There is normally a maximum wood lb core vendor recommendation for either the 12 or 24 hour firing cycle to minimize damaging the core from thermal stress.  The recommendation is essentially based on how much thermal energy you can safely "charge" all the masonry.  You don't want to exceed this recommendation...to do so is similar to overcharging a battery...

As I am sure you already know, masonry heaters burn at 1800+ deg F compared to maybe 600 deg F for a normal wood stove. Consequently, masonry heaters burn much less wood to generate the same total BTU output that you would get from a normal wood stove.  They also burn much more cleanly and the EPA loves them for this reason.  However, masonry heaters release their BTU output over many hours (maybe as much as 24+ hours) so their outside walls typically don't get much hotter than 140 deg F.  Consequently masonry heaters don't overheat the space and they don't excessively dehumidify the space like a normal wood stove.  It can take several hours for the intial heat produced bt the firing to make it thru all the masonry and reach the outside walls.  If you over-fire a masonry heater you may produce thermal stress that exceeds what the design can tolerate.

Again, I'm going from memory and hope this helps.

Bob B.

[sailawayrb]

Huh ??
[/quote]

Yup!

http://www.tempcast.com/planninguide/plan01.html

Bob B.

[rcavictim]

Perhaps one needs to define 'efficiency'.  Example.  "I filled the stove with wood, got it burning and left it for a few hours.  When I checked it after the burn I discovered it had consumed all of the wood I put in, turning 100% of it to ash, smoke and heat.  Must be 100% efficient!"

[mbryner]

Jens, the combustion efficiency of a masonry heater is quite good, if you go back to the white papers from researchers besides TempCast or Heatkit advertising.   In traditional wood stoves, you lose woodgas up the stove pipe, therefore creating more creosote etc., while masonry heaters burn that woodgas because of higher temps.   I'm measuring 900 deg at the metal door of ours.   Of course the newer metal wood stoves burn cleaner w/ secondary combustion zones and catalytic tech.   So compared to a traditional woodstove, yes, you can get more BTU's from a cord of wood when using a masonry stove.   If you run a metal woodstove with dampers wide open, the wood will be gone in a few hours same as a masonry stove, but the stove and air around it will be superheated.   Then the temp will drop quickly of course.    I think the take home point is not how many BTU's you get from a cord of wood, but how the BTU's are delivered to the home: fast or slowly.

Why do you say that unrestricted air flow causes reduced efficiency?  If you give a fire plenty of oxygen you get a complete burn and maximum heat.   If you save the heat before it goes up the chimney, overall efficiency goes up.   When you refer to open fireplaces with 10-15% efficiency are you meaning combustion efficiency or heat transfer efficiency?   I agree: their heat transfer efficiency is terrible.

1) Pick the right heater based on it's BTU output relative to the size of your home's heating requirements.  Perhaps use software like Energy 10 to figure this out.

2) Locate the heater in the center of your primary living area because of radiant heating.

3) Always use seasoned, very dry wood.  Masonry heater cores don't like moisture because it creates significant temp differences across the core that create significant thermal stress.

4) Break it in slowly by starting with very small fires (maybe 5-10 lbs) to slowly drive all the moisture out of the core over a period of several days.

5) Decide on either a 12 or 24 hour firing cycle.  There is normally a maximum wood lb core vendor recommendation for either the 12 or 24 hour firing cycle to minimize damaging the core from thermal stress.  The recommendation is essentially based on how much thermal energy you can safely "charge" all the masonry.  You don't want to exceed this recommendation...to do so is similar to overcharging a battery...

1. Got as big of a heater as I could.
2. yes
3. unfortunately all I have is wet wood currently, looking to get more dry wood
4. did that for many weeks before we moved in, and I used relatively dry wood for that
5. at current exterior temps we have to go w/ q 12 h.

I'm just not used to our stove yet.   The house feels warm enough: the walls feel warm and we don't feel very cold, but the thermostat thermometer is reporting only 64 deg.

[sailawayrb]

While I can see a marginally better performance of a masonry stove in converting wood to thermal energy, I do not see how you come up with the idea that masonry heaters "burn MUCH less wood for the same BTU output" (my emphasis). The web page you reference gives no quantitative comparison (unless I missed it) nor should this page be taken as gospel since after all it is an advertisement.
As a matter of fact, I would say it is likely that a fire with unrestricted air input runs at a REDUCED efficiency compared to a fire where you do not have an overabundance of combustion air (worst case example being an open fireplace with 10 to 15% efficiency).
Of course efficiency drops as you restrict air flow to dampen down a fire. Just like with anything else in life, there is an optimum output with a fall-off on either side. Point is, masonry furnaces have their good points but they do not magically make one cord of wood produce the same heat that another wood stove would require two cords of wood for.
Today's modern wood stove can achieve 90% (some slightly more, some slightly less) efficiency independent of masonry or other construction technique.

There's a combustion efficieny comparison chart in first section of link.  Metal stoves 65%, this TempCast 95%, and wood furnaces 55%.  Whether you want to believe it or not is up to you.  The link discusses that you have to get to at least 1100 deg F before you can extract the energy from the wood gases that would just go up the chimney in a normal wood stove.  That plus the fact that a masonry heater routes the exhaust thru the masonry in multiple passes extracts more BTUs from the same mass of wood than a normal metal stove.  The folks that I know who have switched from their high efficency, EPA certified metal stoves to masonry heaters say they only use about 40% of the wood they previously used with their metal stoves per heating season now.  That seems like a significant efficency improvement to me.  This increased efficency (use less wood to get same heating) is also why masonry heaters were created a couple hundred years ago when they ran out of trees in Europe.

Bob B.

[sailawayrb]

The house feels warm enough: the walls feel warm and we don't feel very cold, but the thermostat thermometer is reporting only 64 deg.

Actually, I think this makes good sense.  The masonry heater is NOT heating the air...it is radiating heat to the surfaces (walls, floor, and people).  Anything not in direct line-of-sight of a radiating surface will not be "warmed".  I have noticed this effect with radiant floor heating as well.  If you are sitting on the couch, all is well.  However, if you lay down on the couch, you start to feel cold because the couch "shadows" you from the floor.  Does your thermostat thermometer "see" the masonry stove?

I think you just need to get accustomed to your new radiant heating masonry stove.  I am looking forward to having one myself...and I would be overjoyed if it will heat domestic water too.  I personally can't live in a house that is heated by a metal stove (wood or pellet).  The air gets way too dry and I'll wake up in the middle of the night with a killer sinus headache.  However, I have done fine with our new propane metal stove.  Of course, burning propane produces water and actually humidifies the space.

Marcus, I think you have a great setup.  I would just try to get on dry wood as soon as you can...as you indicated you would do.  Did Jackson county require you to use outside makeup air?

Bob B.

[mobile_bob]

showing my ignorance or rather my forgetfulness here

there is a professor in colorado that did some pioneering work with woodgas
and all that some years ago

he developed a small single burner kitchen stove for use in 3rd world countries where wood is a rapidly depleting resource.

instead of simply burning small sticks and twigs to cook with, the little table top unit converted the wood to woodgas that was
then burnt to do the cooking, the overall efficiency gain was quite striking

easy to prove the difference to, put a pot of water on a standard wood burner and see how hot x amount of water gets out of
x amount of wood, then run the same test with his little stove, iirc it could do the same with half or less of the fuel consumed.

it makes sense that anytime you can get things hot enough to convert the wood to gas,and then burn that gas it ought to be more
efficient, however it is really hard to do that with a standard stove even if it can take the heat.  most folks don't like to stand around
a stove that is red hot heading toward white hot...

that is my understanding of the russian and similar designs, the massive thermal structure can absorb and moderate the release of this
heat so that you get the heat at a more acceptable rate.

the russian design has its origins in some of the coldest regions on earth, places that are very short on wood,, i figure there is a reason
that they built them that way,, the not only work but use less fuel doing the job?

makes sense to me

bob g

[mobile_bob]

you will heat the outside?

not in a russian, with its labrynth/maze of flue running back and forth through the thermal mass, let 'er rip!

by the time those burnt gasses make it to the stack there ain't much left.

at least that is my understanding of the process

bob g

[Crofter]

I have seen this discussion a number of times about heating devices and efficiency. There is usually a lot of emotional attachment to claims and not nearly enough control on the statistical "facts" and the conditions under which they were collected. Often what seems to be a clenching argument can be easily explained and not overall conclusive at all.

One of the biggest waste of wood is failing to get decent utilization of a given woods volatiles component. With some wood varieties this can be as much as 80% of the inherent energy, on others much lower. The wood gas boys will be right up on this aspect. The masonry heaters burn and firing style scores high in this aspect. It is doable with a continuous burn device but takes more skill and attention.
As another poster with tongue in cheek has alluded, percentage efficiency is elusive game especially when not identified. Unless a continuous log of room temperature and stack temperature is recorded and the wood is identical and weighed, and the weather and heat loss is identical, any claims about wood usage are of questionable value. Hell most wood burners and wood sellers dont seem to know within 50% what is a cord.

The masonry heaters have a lot of good points and certainly lots of charm. I just dont think they are good bang for the buck and might be hard pressed to prove under controlled conditions that they are any more efficient than a skilfully fired epa iron stove being fed the same quality wood.

I just lugged a Drolet HT 2000 down into my sons basement; his Christmas present. Do a google on it. Claims 78% efficiency.

The claim about the Russian heaters efficiency is compared to what? Why masonry... iron wasnt available and labour was dirt cheap. I think Jens is correct about air in excess of that required for complete combustion being a waste of energy. It is according to combustion theory.

I said I wasnt going to get into this, lol!