# The Great Wall of Heat



## byQ (Dec 26, 2016)

I don't think anybody has built this before.

I can already see it. I would love to get this thing engineered out, and build it. What an idea. A long masonry wall 15 to 20 feet long, 7 or 8 feet tall, and 1 or 1.5 feet thick. For new construction - a passive solar house. The wall would be 7 to 15 feet from the house's outer south wall. This wall gets heat from 3 sources. It also has a fireplace for ambiance.

Sources of heat for the house,
*  Passive solar, sun heats masonry from south, large windows, masonry is a dark color on this south side. And, thermal shutters used - opened when sun is out or else closed.

* radiant hot water from solar water collectors on roof - that is, pex-like tubing is installed in the lower part of the wall so heat can be 'dumped' into the masonry from roof collectors..

* 2 masonry heater's are built into the first part and last part of the south side of the wall - so narrow channels run throughout the wall for heat exchange.

A fireplace is built in the center of the wall, on the North/living room side of the wall. And all 3 flues (fireplace & 2 masonry heaters) run up a common center and have separate chimney outlets. 

How would it work? Depending on the heat desired, you would start with heating from sunshine through the windows, next energy transferred from the sun through water, and lastly energy from first one masonry heater, and then the second masonry heater if needed. Spring and fall probably no need to burn wood. Warm winter weather one masonry heater used. Cold spells both masonry heaters used.

For example, a cold winter's day - say -5 F. You start by opening the thermal shutters at around 10:30 am. The sun comes through the windows and heats the wall. At the same time heated water is dumping heat into the wall via solar panels on roof. At 4:30 pm you close the thermal shutters, and the hot water system automatically shuts down as the sun declines.

You check the temperature of the wall. You find it needs to be raised to a higher temperature. You throw some wood in 1 or 2 of the masonry heaters. After 2 hours you shut the flues. Now you have a big hot thermal mass in your house. To relax, you throw some wood in the living room fireplace.

I bet this 'Great Wall of Heat' would use less than 1 cord of firewood a year.


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## jetsam (Dec 26, 2016)

I'd stud out the whole south face of it with 2x8, and cover the whole thing with cheap double pane vinyl picture windows.  Several layers of black fiberglass window screening an inch or two behind the windows, and paint the masonry in back flat black.  Now all you need is a hot air outlet at the top and a cool air inlet at the bottom, and you have a giant solar heater that not only provides hot air, but also heats your wall.

Now you can use the solar heater on the roof to preheat your domestic hot water instead of the wall, too.


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## jebatty (Dec 26, 2016)

I think the "great wall of heat" has been built by quite a few people, and is a very old idea. It can work, more or less, but keep in mind that masonry heats very slowly and releases heat very slowly, just as a radiant slab.


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## byQ (Dec 26, 2016)

jebatty said:


> I think the "great wall of heat" has been built by quite a few people, and is a very old idea. It can work, more or less, but keep in mind that masonry heats very slowly and releases heat very slowly, just as a radiant slab.




Ya, there isn't anything new here. It is just combining several things together. I think radiant/slow heat is the best kind. This wall would take a lot of materials to construct.But once done it would 'quietly' do its thing.

I would like to see how this wall performed in a 2000 sq ft house with above average insulation. This wall would be a btu nerd's dream problem - they could measure the thermal mass & heat in from the different sources. I like the idea of the wall working to heat for you without you having to do much of anything - just open and close shutters. If it gets cold you charge it with some firewood. 

This is more like something people would do in Europe. In North America we are forced air duct addicts.


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## peirhead (Dec 27, 2016)

Known as a *Trombe *wall The only downside I can see is it blocks the nice sunshine from coming right into the house..what I want is a huge piece of glass that could store the heat put pass the visible light!


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## woodgeek (Dec 27, 2016)

I think the description is a bit different than a Trombe wall (which never worked that well).

That said, the 20th century is over, and now superinsulation is where its at.  The great wall is way more effort and cost (in new construction) than just insulating to about half passive house levels, and running a minisplit + electric backup for ~$300/year (less than basic cable).

Then if you want wood heat, get a small stone cat and fire it once a day, twice if it's arctic out.


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## byQ (Dec 27, 2016)

peirhead said:


> Known as a *Trombe *wall The only downside I can see is it blocks the nice sunshine from coming right into the house..what I want is a huge piece of glass that could store the heat put pass the visible light!



On your wall we'll build in some glass blocks so the southern sun light can get into the living space but isn't too bright. Actually that is a good idea - so glass blocks sections in the great wall.


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## byQ (Dec 27, 2016)

woodgeek said:


> I think the description is a bit different than a Trombe wall (which never worked that well).
> 
> That said, the 20th century is over, and now superinsulation is where its at.  The great wall is way more effort and cost (in new construction) than just insulating to about half passive house levels, and running a minisplit + electric backup for ~$300/year (less than basic cable).
> 
> Then if you want wood heat, get a small stone cat and fire it once a day, twice if its arctic out.



Your energy loop is using more modern means. It would work nicely. And if you had a solar pv panel to run the mini split the energy loop would take care of itself. But I like the non-mechanical means, too - the 'the el natural' option. 

Both are trying to do the same thing - install a system that requires very little energy cost once in place - mine old school, yours modern.


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## Dobish (Dec 27, 2016)

i just put in a 9' sliding door on the south wall of my house. with the sun up and the shades open, it stays nice and toasty, and it blinds us sitting at the breakfast table.


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## woodgeek (Dec 27, 2016)

byQ said:


> Your energy loop is using more modern means. It would work nicely. And if you had a solar pv panel to run the mini split the energy loop would take care of itself. But I like the non-mechanical means, too - the 'the el natural' option.
> 
> Both are trying to do the same thing - install a system that requires very little energy cost once in place - mine old school, yours modern.



Nothing mechanical about super-insulation, works for decades with no moving parts.  Most passive solar thermal mass technology have high parasitic heat losses through the glazing.  Combining a masonry heater with a passive solar thermal mass just means higher parasitic losses through the glazing of your wood heat.  If you don't like mini's and want passive solar, then superinsulate, use a smaller amount of high performance south facing glazing, and your interior framing and drywall provide all the thermal mass you need or want.  And put in a smaller stove.

The high mass- high glazing area (and low -R glass) passive solar technology of the 70s never worked well at all, which is why it was never mass adopted.  The german-style 'passive house' superinsulation is often a bit overdone in terms of cost/benefit.  Read about 'Pretty Good House' design for current price/performance optimum and tech.  With some wood-fired point heat sources it can be very cheap and comfortable with little/no mechanical systems and great 'passive survivability'.


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## byQ (Dec 27, 2016)

You mean heat loss through the south facing windows? Simple thermal shutters are used to limit this loss - shutters opened, sun heat in, shutters closed - heat stays in.


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## woodgeek (Dec 27, 2016)

There is still parasitic loss during the day.  This increases with the temp of the thermal mass, which is why combining masonry heaters with solar thermal masses was never a popular strategy...its a bad idea.

You would want to shop for glazing that is both low-E AND high solar gain coefficient (SHGC) to avoid these losses.  This glazing exists, but is not widely available or cheap.  In the north, people usually buy low-E, and in the south, low SHGC.  So most mass-produced windows are both.  In the end, such solar glazing would likely be more expensive than superinsulation.

Thermal shutters were another technology that had poorer than expected performance, and was generally a PITA.  Do you open the shutters on cloudy days?   Do you look at a forecast in the morning?  If the sun is coming out for an hour or two, do you then open, or not?  What if it gets cloudy for an hour in the middle of the day...do you close up then?  A half hour?  Most people eventually get bored and give it up, and eat the higher parasitic losses for the life of the structure.

A lot of glazing will overheat if it has a shutter and the sun is shining...and the seals will fail.  So you would probably need to open them on cloudy days lest the sun come out while you were away or didn't notice an ruin your expensive glazing.

If you went active solar for space heating, you would almost certainly NOT run it into the masonry.  You would likely put it into an insulated water tank in the basement.  This way you could use it for domestic hot water 12 mos a year (if it were sized for space heating).  Not only is this cheaper thermal mass, it also give you control.  If you messed up and overheated your space, you would need to open a window ( a common occurrence in passive solar heated structures, especially in the shoulder seasons ) and would have to shut down the active solar.  This overheating problem does not occur with the water tank....you can circulate the heat or not to conventional hydronic radiation with a thermostat if you want.


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## byQ (Dec 27, 2016)

I would just go with 'normal' double pane glass. Great windows with multi panes and gas filled costing a fortune can be outperformed several times over via low cost shutters made of rigid board insulation and a neoprene seal. Some monks did it this simple way and have had no problems with seals. Those windows would need to be shatter proof (for when you forgot to open the shutters on a sunny day or windows might crack).

On days where the sun wasn't shining, you would need to 'charge' the wall via burning firewood. I would close the shutters and fire up one or two of the masonry heaters. As far as heat needed, (and when to open/close shutters) you would need to just feel your way through the system and find what works.

Probably if you were to combine your super insulation with 'the wall' you might only need a little wall and not so much south glass. And maybe one micro masonry heater built into the little wall or a mini minisplit.


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## woodgeek (Dec 27, 2016)

Compute the thermal mass of the drywall in a conventional house, as compared with a masonry heater.  

The thermal 'cruise' time for a structure is the thermal mass times its thermal resistance to the outside.  Once you insulate properly, the cruise time becomes long without adding any (extra) thermal mass.  In other words, you have to have poor insulation for the thermal mass to have any real function.  So insulation gives comfort, lower energy needs AND buffering of wood heat and solar input, while thermal mass only gives the last two.


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## St. Coemgen (Dec 30, 2016)

As others already said, it has been done. Nothing new.

Seriously, stop trying to re-invent the wheel in these posts. If you are interested in "free" and passive heating, just build an Earthship.


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## Circus (Dec 31, 2016)

byQ said:


> I don't think anybody has built this before.
> 
> 
> I bet this 'Great Wall of Heat' would use less than 1 cord of firewood a year.



Google "medieval masonry stove". Idea is only about 1000 years old. Burns fast, hot and clean with little smoke then heats slow and long. Works good.


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## Karl Hungus (Dec 31, 2016)

I've looked into passive solar. Talked to several people that have them.
Trouble is the sun does not shine every day.
In my neck of the woods we go for days maybe even weeks with no significant sunshine in the winter.
When the sun shines its great. When it doesn't its a big heat drain.
Down side with a masonry heater is you don't fire it up for one or two days then leave it for a week or two.
It takes time to build the mass of heat.
You really need to fire it daily. Maybe once or twice a day or with smaller loads but you have to keep the flywheel turning.
The solar hot water heater would probably be a better solution if you heat a large mass of water and use it also for DHW.
I think your trying to make too many "systems" work together and you really don't need all of them. Just extra cost and complexity.
Also you'll need an engineering degree to figure out when to run what and how much heat what is going to generate on what kind of day/weather.
Keep it simple.
Insulate to over R30 on walls and R50 in the attic, good windows and pick either the masonry heater or the solar water heater and you'll be good to go.


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## byQ (Dec 31, 2016)

Karl Hungus said:


> I've looked into passive solar. Talked to several people that have them.
> Trouble is the sun does not shine every day.
> In my neck of the woods we go for days maybe even weeks with no significant sunshine in the winter.
> When the sun shines its great. When it doesn't its a big heat drain.
> ...



This system would be simple. No sunshine - close the thermal shutters which are R-30. You aren't starting the wall from zero - it had collected heat from the day before. Throw your firewood into the fireboxes. The wall is thinner than a normal masonry heater so it dumps its heat into the living space quicker. No heat the next day - fine -throw more wood in the masonry heaters. Next day the sun is out - throw half a load in one of the masonry heaters - wow how complex!


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## spirilis (Dec 31, 2016)

If you need some masonry heater porn, check out the book "The Book of Masonry Stoves" - https://www.amazon.com/gp/product/1890132098/?tag=hearthamazon-20

Fascinating history of the technology.


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## Easy Livin’ 3000 (Dec 31, 2016)

byQ said:


> This system would be simple. No sunshine - close the thermal shutters which are R-30. You aren't starting the wall from zero - it had collected heat from the day before. Throw your firewood into the fireboxes. The wall is thinner than a normal masonry heater so it dumps its heat into the living space quicker. No heat the next day - fine -throw more wood in the masonry heaters. Next day the sun is out - throw half a load in one of the masonry heaters - wow how complex!


byQ, there's only one way to know how it would work for you, and I bet we'd all love to hear your story once you've got it done and lived with it for a couple of years. Only idea that I have to offer is some sort of thermostatic control of those shutters. I'd grow weary of manually opening and closing, plus don't you ever want to vacation away from the place?


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## byQ (Dec 31, 2016)

ED 3000 said:


> byQ, there's only one way to know how it would work for you, and I bet we'd all love to hear your story once you've got it done and lived with it for a couple of years. Only idea that I have to offer is some sort of thermostatic control of those shutters. I'd grow weary of manually opening and closing, plus don't you ever want to vacation away from the place?



There are some bugs to work out - I need to get some building advice from some masons. First off, you are making a wall that is narrower than a typical masonry heater - so your channels are longer but less in volume. Also, your fireplace and 2 masonry heaters will need to be deeper than the wall and stick out from the wall - I don't think this is a problem, building wise.

The Russian type of masonry heater with horizontal channels would be what you would want for a wall. This double heater wall would be for a larger type house, say 3000 sq. ft.. You could shrink the wall for a smaller house - and maybe just install one masonry heater.

It would take 5 minutes to open and 5 minutes to close the shutters, and the shutters are on the inside of the house. That isn't much work. If you went on vacation in the winter you would just leave the shutters open.


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## jebatty (Jan 1, 2017)

Energy savings means and dreams are fun. Most of us have had and still have them. My deja vu dream was a secure energy source when the end of oil arrived. Thought was to acquire some peat land. Then I realized (oh, really?) that my forest land was that secure energy source. Energy security stared me in the face and I didn't see it. Hence, our 1956 house with fair insulation, very good windows and passive solar to the SW, along with a wood stove in the living room, is well situated to be a very simple, inexpensive, and secure "great wall of heat" that can slay the coldest and windiest weather northern MN can throw at me.

BTW, the "end of oil" in the view of "The Long Emergency" (2005) by James Kunstler, at least in the sense of very high cost and falling supply, looks a long way off. The real "long emergency" we now face more than likely is clean water scarcity, extinction, and environmental destruction caused by, yes, human folly and lack of will to pursue clean energy with a vengeance. The Earth we treat as a trash dump may well be a long way down the long emergency path and doing a very good job of trashing life as we know it.


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## Circus (Jan 1, 2017)

Karl Hungus said:


> In my neck of the woods we go for days maybe even weeks with no significant sunshine in the winter.


In Wisconsin the warm gulf winds bring the clouds and the bitter cold Canadian air brings the sun. Solar works best when needed the most.
I disagree with almost everything Karl said except "your trying to make too many systems work together".
Masonry stove is a good idea.
Low mass solar hot air collectors act like a window when the sun shines and an insulated wall the rest of the time. No shutters, no monitoring, no work, no windows. Main disadvantage is the temperature swings which your masonry thermal mass would help buffer. 
I use solar for domestic hot water because it's smaller and useful year round but it would be too expensive and too much hassle to use as heat.


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## Karl Hungus (Jan 2, 2017)

byQ said:


> This system would be simple. No sunshine - close the thermal shutters which are R-30. You aren't starting the wall from zero - it had collected heat from the day before. Throw your firewood into the fireboxes. The wall is thinner than a normal masonry heater so it dumps its heat into the living space quicker. No heat the next day - fine -throw more wood in the masonry heaters. Next day the sun is out - throw half a load in one of the masonry heaters - wow how complex!



The whole idea of a masonry heater is thermal mass, no mass to store heat its just a wood stove. Now its less efficient, you use more wood and you have to stoke it constantly to get heat. I thought you wanted this giant wall of mass to store heat? now your saying you want less mass to make the masonry heaters heat up fast. Which is it?
Just another thought, do you have an idea on how much you want to spend on this wall? Got an idea what a masonry heater costs? much less 2 of them not to mention the fire place in the center. How much are you willing to spend on your solar water heating system?

Your first step in your new house should be building it air tight with a HRV or a ERV, then insulate well beyond normal insulation levels.
One of the reasons you do this is to reduce the size of the systems required to heat and cool the place.
When your at this point and you do a heat load calculation you find you don't need 2 masonry heaters, a fireplace and solar hot water heater not to mention the passive solar.

What are you going to do for "reliable" heat? What if you break your leg and are bed ridden for a week or you want to go on vacation for a week?
Another advantage of super insulation is if the heat goes out you can go for a much longer time before your pipes freeze.

I've got a workshop with 6" slab of concrete that is hydronically heated and it has 2 x 6 walls. The water heater went out in 0-10 degree weather. In one week it dropped from 65 to 43 degrees.  I know my garage with 2 x 4 walls and a forced air heater has no heat in less than 2 days when I turn off the heat.


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## byQ (Jan 2, 2017)

You want it thinner than a normal masonry heater because a greater surface area will collect more of the sun's radiation - remember this wall is orientated inside the house and is absorbing the sun's rays - so make it dark on the south side. And it is thinner to allow the solar energy it gathers to travel to the other side of the wall quicker (the living room side - where you want the heat). Actually the mass of the wall will be greater that a normal masonry heater (it is thin but long).


What are you going to do for "reliable" heat? What if you break your leg and are bed ridden for a week or you want to go on vacation for a week?

You open the thermal shutters and plug in a wall heater.

I've got this set-up in the house I'm building but I have the 'walls' separated from the masonry heater. I look at this set-up and I realize I could combine the two. Two masonry heaters in this set-up would be for a large house (no so untypical). My house is well insulated and mid-size so I would have just put one masonry heater in the wall.

And if you were to build a house that is tight with really good insulation - you could build the wall for free heat and omit the masonry heaters. Your backup plan when there is no sunshine? Maybe a wall heater or a small wood stove.

I'm guessing I could build this wall for about $3000 in materials - thermal shutters, 2 masonry heaters, 2 water solar panels, a water tank,shatterproof south windows, lots of firebrick, etc...


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## semipro (Jan 16, 2017)

Two comments:
Don't underestimate the potential thermal mass of a structure.  I've been struck by the thermal cruise time that our house has due to masonry and plaster throughout.  This can work against you though when you're trying to warm up a cold house.  I continue to be amazed how long it takes to warm our place up. It makes it easy to appreciate the concept of a super insulated, low thermal mass house especially if your prefer your house cooler at night for better sleep yet warm when you wake up. 
As solar PV costs fall, the ROI break-even point between investing in things like passive solar or insulation versus investing in PV continues to move in favor of PV.


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