Building a massive hearth for a wood stove.

[gnawrot]

homefire - 18 September 2006 11:49 AM
Building the walls will block the heath you get from the unit.
You will need to burn longer and hotter to achive the desired
comfort level you are seeking.

I might get heavy-duty unit say Dutch West large and burn wood full power. Walls will absorb some heat, which will be released when wood stove will be off.

homefire - 18 September 2006 11:49 AM
I don’t understand your thinking about time to build a masonary heater
seems if you have the tools ,skills, and knowledge it would be a piece of cake for you.

Well, I have a humble approach. I don’t want to underestimate any project. I assume that everything is difficult so I put my best with intensity. If projects turned out easy that is fine. I don’t want to say it was easy. I deal with different projects: plumbing, roofing, electrical, painting, woodworking, car repair, PC repair, phone line repair etc. I am master of none but I am doing quite well in any of them.

As far as masonry heater is concerned. Well, I fixed chimney last year because it needed to be re-pointed. Some of my brick layering was done pretty crappy. I started doing decent job on my fifth row of bricks. I asked my Brother-in-law to help me and he did much better job (really good job).

So my brick, tile layering skills are pretty low. I can deal with concrete quite well (I poured concrete chimney cap – weighing around 130 lbs), which was put on the top of the chimney.

Is there a website which show you how to build a masonry heater?
Is there a vendor that supplies some parts of masonry heater?
Are there any books available on how to build a masonry heater?
Are those masonry heaters indeed more efficient than NC wood stoves?

 

[Homefire]

(broken link removed to http://mha-net.org/msb/html/faq.htm)

good luck

 

[Rhone]

The problem with using a wood stove as the core, there's metal. You can't burn it care free, overfiring can cause damage to the stove. An all masonry unit laughs at overfiring. NY Soapstone gave great advice on something that accomplishes storage, also provides convection heat, aesthetically pleasing, inexpensive, and your floor can support it. Very practical. If you're going to turn this into a masonry heater, which as a retrofit I think is crazy unless you tear your house down and rebuild around it, http://mha-net.org/msb/html/guide.htm has a kit I suggest you get instead of trying to figure out the balance & physics. Click on the pricing though... that's just for the materials & design. Really makes NY's idea shine.

 

[Rhone]

As a tip, radiant heat shoots straight out of flat surfaces and power is stronger the bigger the surface. It's not like ambient light, it's focused energy. Stand directly on a wood stoves flat side, and you'll feel radiant energy start warming you. The bigger the side, the more powerful. Next, stand beside one of the smaller sides, it won't be as powerful. Lastly, stand diagonal to the stove, so none of the sides face you and... you'll feel very little radiant heat if any even right next to the stove. That's why wood stove clearances are less putting it diagonally in a corner vs. square in one.

In NY Soapstone's idea the wall around the stove should be circular so there aren't big flat surfaces. That will disperse the radiant heat more evenly around the room instead of creating hot/cold spots. Also, the front of the stove where there is no wall, will be the coldest place sitting in front of when the fire's out, and the warmest place when it's going. Something to think about, and maybe design the Feng Shei of the room around.

 

[wg_bent]

Look back to my previous post. The blue text is a hot link to a pretty neat set of pictures.

 

[BikeMedic2709]

Gnawrot,

You have said that concrete is cheap. Where are you getting cheap concrete? Don't hold out on us. Where I am it is $75 a yard.

 

[wg_bent]

Gnawrot,

You have said that concrete is cheap. Where are you getting cheap concrete? Don't hold out on us. Where I am it is $75 a yard.

That's cheap mass in my book. At roughly 100lbs /cuft, that's 2700 lbs for $75. Not expensive in my book...unless your doing a driveway.

What is added to make it refractory material?

 

[BrotherBart]

Ok. I gotta ask. Is not the the heat that isn't being soaked up by all of this thermal mass being absorbed by and released by everything else in the house? All of that neat stuff like interior walls, furniture, the Harley sitting in the living room etc.

 

[gnawrot]

Having 2700 lbs of concrete for 75$ is cheap in my book too.

Funny thing was that I purchased 3 bags of Portland cement (94lbs each). Added sand from my property and crushed stone which I had too. I mixed around 2000 lbs of concrete for 30$. I purchased 22 tons of crushed stone last year and I had some leftovers. Having crushed stone in a concrete was a hassle but it was just for footing of the playset I am building now. Playset is made out of black locust so it should last a while. I might need to replace fasteners before wood but this will not be done by me.

I would not want to deal with this again for hearth though. I would purchase either concrete in bags or get mixed concrete delivered.

EDIT: Some people find making concrete deck cheaper than using PT pine.

 

[cbrodsky]

Building the walls will block the heath you get from the unit.
You will need to burn longer and hotter to achive the desired
comfort level you are seeking.
I don't understand your thinking about time to build a masonary heater
seems if you have the tools ,skills, and knowledge it would be a piece of cake for you.

The best hearths I have seen in homes from Washington to New York are supported from the ground up with
solid masonary work.
I owned a home once that had a masonary heater that had 3 flues and was 20 ' tall and 6x 8 at the base down to 3x 3 on the top floor where there was a smaller hearth for hot coals to provide quick heat for the sleeping areas.
That heater was built in the early 1800's
Wish I had one like it today.

Good luck to you gnawrot

You are correct in that adding something to soak up heat, to a point, will consume some of the stove output. So, this idea will not help you at all when you are running your cast iron/steel stove 100% at the higher end of allowable burn range. But I know for me, those days are very limited. I think the objective of such a setup would be to run the stove hotter during much more of the burn season, but perhaps not as frequently. This gives you the chimney cleaning benefit of running hot fires all the time, not trying to choke down your burn rate in shoulder seasons, and still helps dampen out the heat response. I see a lot of posts of "how can I stretch out the heat cycle on my stove" and "it's too hot to burn because the stove gets crazy hot" - this is what you address with a masonry heater or large well placed thermal mass.

As others have noted though, you will ultimately be limited by the output of the stove - this basic principle cannot be missed!

-Colin

 

[gnawrot]

Should I get large wood stove such as Dutch West large or can I get just medium size DW or Madison? How is Madison compared to Dutch West?

 

[Harley]

the Harley sitting in the living room etc.

Actually, mine goes in the bedroom for the winter, not the living room.

 

[brian_in_idaho]

Never said you could get a Tulikivi installed for 5k. I just mentioned a 5k Tulikivi. I agree...another 5 to install.

Might be interesting to get hold of the masonry heater association to see what one of these would cost: Small Heater

It almost looks like you could build it your self just from the pictures they include there. Face it with some nice brick and that thing might be s nice "little" heater.

Warren, this system looks pretty interesting and managable by a DIYer. I couldn't find any info on that site where they sourced the kit, have you seen anything? A few years back when I designed my house I looked hard at some of the pre-fabbed "cores"-they were pricy and still required a pretty skilled mason to do all the joints in the area in contact with the flue gasses. I don't have the nerve to try that, but don't mind doing "cosmetic" masonry, cultured stone or brick facing. That kit in your link looks like it might work well for that.

Bri

 

[gnawrot]

I purchased brand new VC Madison in black finish for 1K (I hope it is a good price). I did not want to deal with building a masonry heater. Thanks for all tips though - it was quite exciting and very interesting.

Now I will explore building hearth based on wood stove design with wall on side and high stone wall in the back of the stove.

 

[Martin Strand III]

Hi Guys:

Late to chime in but everyone so far has missed the point as to why this woodfired homemade concrete monolith won't work well to heat your home and possibly could ruin it.

Probable inadequate floor support reasons aside, the main reason one cannot heat up a large masonry mass (FYI: concrete is lousy thermal mass medium for heat banking) with a rather puny fireplace insert is that this heating device, and all its woodburning metal cousins, does not get hot enough. Any metal stove will require choking down air supply so as not to overfire and damage the stove. This is well below the best temperature to burn wood. And this is not good if you want to heat up a large mass of masonry.

Masonry heater fireboxes, in comparison, are designed and built to burn wood with the air supply wide open to obtain and withstand temperatures well above those reached in its firebox (approximately 1800* F) to heat the masonry which is constructed with masonry materials optimal for moderate heat transfer (unlike metal which has high heat transfer) through the thermal mass and eventually, as radiant heat, out to the objects in the room.

In short you are trying to design a system to heat masonry mass with a heater that will put out only, say 55,000 BTU, whereas you'll need somewhere between 250,000 - 350,000 BTU to do the job.

In other words, you cannot run with the big dogs on the track burning hi tech nitromethane while you burn lamp oil.

Check out another home grown system here: http://www.backwoodshome.com/articles2/lee90.html

Aye,
Marty

Grandma used to say, "The Devil is in the details."

 

[Martin Strand III]

Woops:

While I was typing and gabbing on the phone, more was covered beefore I posted. I think you're gettin' it.

Here's another small masonry shop heater: (broken link removed to http://www.turtlerockheat.com/gal_shop.html)

Aye,
Marty

 

[cbrodsky]

Hi Guys:

Late to chime in but everyone so far has missed the point as to why this woodfired homemade concrete monolith won't work well to heat your home and possibly could ruin it.

Probable inadequate floor support reasons aside, the main reason one cannot heat up a large masonry mass (FYI: concrete is lousy thermal mass medium for heat banking) with a rather puny fireplace insert is that this heating device, and all its woodburning metal cousins, does not get hot enough. Any metal stove will require choking down air supply so as not to overfire and damage the stove. This is well below the best temperature to burn wood. And this is not good if you want to heat up a large mass of masonry.

In short you are trying to design a system to heat masonry mass with a heater that will put out only, say 55,000 BTU, whereas you'll need somewhere between 250,000 - 350,000 BTU to do the job.

The point that you still have to hold your stove to the same surface temperature standards is indeed valid. And I would not recommend putting any thermal mass so close that you are unable to sink the stove heat without it overheating - I don't think anyone is suggesting enclosing a stove in concrete - at most placing thick heat absorbing walls near the stove. Remember even a 1" airgap drives a lot of cooling convection and does wonders to enable close clearances with offset wall protection - a few inches of airspace between your thermal mass and stove will let the stove operate fine without overheating itself, yet still effectively radiate a lot of heat into a thermal mass until it reaches equilibrium.

Also, as to "doing the job" that is somewhat subjective. If you store 55,000 BTUs in your thermal mass after reaching equilibrium with your wood stove, that will heat some houses for hours much of the winter after your fire burns out. Not 24 hours, but a few hours depending on season. That could be very valuable for some folks in terms of keeping their oil heat off while away for a long work day; could be useless for others with a drafty old house. And it'll definitely price out much closer to the standard woodstove install rather than the 5-figure masonry jobs.

If you look at it from the perspective of how you'd run your stove, as noted above, few of us probably run our stoves full bore 100% towards upper allowable temps all that often. So even a smaller 40,000 BTU/hr stove could have lots of extra peak capability that is not regularly used, and could thus be dumped into a thermal mass over a few hours of more aggressive burning for release later.

Speaking from experience, even by accident, I'm seeing this work to a limited degree in my setup and realize I could have exploited it for a lot more had I just filled the half wall and put a metal support post right under it in the basement. Would have cost me no more than a couple hundred total.

Don't get me wrong - I would love to have one of the true masonry FP setups and really like the idea if you've got the cash, but at the same time, there is value with an intermediate solution as well if well thought out. When I was building my house, I could not entertain another $15K for a stove. In fact, I couldn't really justify the $10K HS TARM + water storage option I looked into when oil was $1.099 but wish I had come up with the money for that one

-Colin

 

[Martin Strand III]

Colin:

I am sure you are correct: that there are "intermediate" solutions out there to help folks save feeding the big conglomerants (oil, gas, electric, etc) short of investing five figures in a true masonry heater. See my previous post above. However, until there are examples that have some positive track record, respectible R & D, and are available to the average wood burning enthusiast, I maintain home made "intermediates" are at best conjecture and, at worst, possibly inneffective, a waste of the so-called builder's time and money and probably dangerous.

Aye,
Marty

 

[elkimmeg]

I purchased brand new VC Madison in black finish for 1K (I hope it is a good price). I did not want to deal with building a masonry heater. Thanks for all tips though - it was quite exciting and very interesting.

Now I will explore building hearth based on wood stove design with wall on side and high stone wall in the back of the stove.

Not a bad stove or price. That model was discontinued a year or two back. Too many competing models in the same heat range for VC, so they dropped it.

 

[gnawrot]

If I put a stone wall in the back of the stove and on one side (if I decide to pursue this route) and keep recommended clearances I see no reason why I could not benefit from heat storage offered by stone (or whatever material).

EDIT: I already have hot water baseboard heating system in my house. Gas furnace heats up water. This stove will not replace whole heating system. I just want to put wood stove in place of falling apart fireplace. I purchased my house slightly more than one year ago. House needed lots of work and fireplace was not a high priority. However, it will be done before this winter. I want to heat up just lower level of my house if possible. My lower level is probably 1400 sf so Madison should do it more or less. If stove does not generate enough heat it I still have baseboard hot water heating.

EDIT 2: What is a cord of wood?

EDIT 3: Never mind EDIT 2. This is what I found out from wikipedia.

The cord is a unit of dry volume used in Canada and in the United States to measure firewood. One cord is defined as 128 ft³ (~3.62 m³), corresponding to a woodpile 8 ft wide × 4 ft high of 4 ft-long logs. In the metric system, wood is usually measured in steres or cubic metres: 1 stere = 1 m³ ≈ 0.276 cords.

In the United States, the cord is defined by statute in most states. Wood is also sold by the "face cord", which is usually not legally defined, and varies regionally. For example, in one area a pile of wood 8 feet wide × 4 feet high of 16"-long logs may be sold as a "face cord", though its volume is only one-third of a cord. In another region, or even from another vendor, the volume of a face cord may be considerably different.

 

[cbrodsky]

If I put a stone wall in the back of the stove and on one side (if I decide to pursue this route) and keep recommended clearances I see no reason why I could not benefit from heat storage offered by stone (or whatever material).

Correct. Only debatable point is just how much you will store - certainly not hundreds of thousands of BTUs like a true masonry heater, but you will definitely store tens of thousands of BTUs.

And again, if you're staying non combustible, the clearance can be much closer - just leave a few inches of gap for good convection currents to keep the stove within target.

-Colin

 

[Martin Strand III]

EDIT 2: What is a cord of wood?[/quote]

Gnawrot:

Cut and stacked, one cord is 4'x4'x8' = 128 cu ' = about $200 purchase price (northern MI).

But if you are buying your wood, are you really saving on fuel (gas, electric)? Since, to heat that masonry mass, you are going to need a lot of wood.

Aye,
Marty

Grandma used to say, "Be sure to see the forest AND the trees."

 

[gnawrot]

Marty,

I have 2.7 coords of hardwood (mostly oak and a little of maple), which came from trees I cut on my property. I don't plan to buy hardwood but to get it for free. Some people advertize. How long will 2.7 coords last when using 40K BTU woodstove? Thanks for all tips.

EDIT: My wood shed can accommodate 3.8 coords.

 

[Rhone]

In upstate NY, by sounds your house is old, my guess you need 5 cords for the winter. You have about half. I find January and February are usually the coldest months, I'd try to maximize the wood use for then.

Save a weeks supply for emergency. You don't want to risk a storm coming through late knocking out power for several days and you've run out of wood.

 

[gnawrot]

My house is 36 years old and has exterior walls insulated with cocoon (probably around R13). I have ceiling insulated (R38). One room above crawl space has ceiling insulated (R13 and this room is definitely the coldest). Floor is insulated partially.