Mass Heaters without the mass?

Just had an inquiry about rocket mass heaters for apartments, and other situations where a low-mass heater might be necessary for structural reasons.
(Boats, RV's, and manufactured homes might also fall into this category.)

There are several reasons why a rocket mass heater might not be the best choice for such a situation, and ways to use the same design principles to improvise something else that might be suitable.

We've definitely run into problems with rental spaces in general, especially when the landlord is incommunicado about permanent alterations. Even if the landlord is in favor, there are other hassles to get through.

Exhaust issues:
- Apartment buildings are often taller than single-family residences, meaning the building itself can act more like a chimney and have more severe negative-pressure or wind gust problems.
- If you are trying out your idea in someone else's space, you need it to work from the get-go. The most reliable exhaust for good draft is a conventional chimney, exiting above the roof and any nearby obstacles.
In some buildings that can mean going through someone else's space or tacking a lot of insulated stovepipe (spendy) onto the outside of the building.
- For a horizontal vent, there are some detailing issues with water but the most important thing is the wind. If you are on the upwind side of the building, or near a corner that creates gusts and eddies, you may not be able to do a horizontal exhaust without the stove backdrafting in certain wind conditions.
- An outside air supply could be one way to neutralize many of these issues, but it too must be protected. Ideally, it would be in the same place with regard to wind and building pressure (maintaining a neutral balance) but would not be close enough to intake the exhaust.

Mass issues:
- Mass heaters store heat using the dense thermal mass, usually earthen masonry or conventional masonry (brick, stone, etc). Heat storage seems to correlate with density: heavier materials store more heat. It is possible to make lighter masonry heaters, but they are still heavy compared with iron stoves and can't store as much heat as full-mass masonry heaters.
- The mass of a typical rocket mass heater is usually 120-200 lbs/sf. That's comparable to light industrial use, library stacks, or a large aquarium or waterbed. Not impossible that an apartment floor could handle it, or can be reinforced to handle it, but tricky.
- Shoring up or creating a masonry foundation may require work underneath the floor. If there is another apartment below, there is more inconvenience, cost, and risk/liability compared with a ground-floor heater that can't fall on anyone.
- Adding thermal mass of any kind may reveal or create structural issues, especially in older apartments. Old or hidden problems like a leaky shower can lead to rot, and sooner or later the entire bathroom lands in the downstairs neighbor's lap. You don't want to take the risk or blame for precipitating a last-straw situation. Find out the design limits, check that the building is still in good condition to handle these loads, and then keep track of the extra mass you are adding. Try to stay below 1/2 of the load limit on any given square foot. You can also measure the floor level and distance from a nearby fixed point, such as the garage floor below a loft apartment. If you notice any deflection (bending or tilting) of ANYTHING, stop adding mass, remove some, and address the structural issues.

No-Mass issues:
- Without the mass, there is not heat storage.
- Exposed horizontal stovepipe is widely recognized as a firetrap. Even if you are confident you can work around the dangers, there is little chance of official approval.
- Pebble-filled mass heaters do not offer a secondary seal like full-masonry heaters, so hidden leaks are possible. They also may not store or transmit heat as efficiently (a number of people are trying this out and we're looking forward to more data).
- Good insulation seems to be the most popular and effective low-mass option. If it's possible to improve the insulation, the heating loads get much smaller, and smaller heaters can handle these loads. Portable dwellings particularly suggest insulation, as mass and heater fuel are both costly to haul around.

Legal / social issues:
- Rental properties and their owners are often held more strictly to local building codes and insurance requirements, where owner-builders have more freedom to proceed at their own risk.
- Permitting and approval of mass heaters can be expensive, difficult, and time-consuming; local officials may not know how to apply existing code to an EPA-exempt, site-built, hybrid mass heater.
- Putting in a heater without attracting notice from the landlord and/or building officials may be difficult given the need for an outdoor vent (and possibly an outside air source).
- If permitted under the Masonry Heater ASTM standard, one of the requirements is a 12" thick, reinforced, non-combustible foundation starting below frost level or 12" below grade.
- If they are willing to consider an installation over existing suspended (wood) floors, the alternative appeals process may be slow and/or spendy.
- Renters have a reputation among landlords for mistreating property and appliances. The landlord may be wary of letting one renter build an unusual mass heater, as it might not appeal to future tenants (or they might not be responsible enough to run it safely). Unusual things can just be more of a hassle to manage in a rental situation. A long-term lease agreement might alleviate some of these concerns.
- A 'portable' mass heater could resolve some of these issues, but the landlord's permission is likely still required for both installation and removal. (Some rental agreements make any installations the property of the landlord.)

Benefits of small / interior-walled spaces:
- On the plus side, apartments usually have a much smaller heating load, so a more compact masonry stove might not need the same mass to produce a similar balance of warmth.
- Smaller, more sheltered spaces are easier to heat. This means apartments in general need less heat than a comparable exposed dwelling. A small, super-insulated space can be heated with body heat, cooking, or a candle. Cupboard-beds, four-posters, blanket forts, and Paul's article about saving 87% on his heating bill are examples of what can be done by reducing the space to be heated. Many steps can be taken to increase comfort even if you don't own the walls.

Workarounds:
- Portable / Pebble style rocket mass heater: You could consider a lower-mass heater such as Paul Wheaton's pebble-style / box-and-fill construction (also removable should the need arise).
- Smaller masonry heaters: European apartment heaters, and a few American manufacturers, include moderate-mass masonry heaters. You could look into a Tulikivi heater, or a soapstone woodstove, then use it as a springboard to discuss less-expensive "hybrid options" (rocket mass heater). Kiko Denzer's 'Heater Hat' is a clever example of a tiny masonry heater built onto a woodstove.
- Improved radiant heat: If the apartment already has a fireplace or wood-fired heat source, you could look at improving that heater (e.g. with a Rumford retrofit) and/or creating more storage to sustain the warmth after the fire is out (a brick hearth or backsplash designed to catch radiant heat from the stove, dense 'art' or brick 'end-tables' in front of the fireplace, a heater hat as above, or just pile bricks on the stove....
- Passive-solar techniques: You could also look at improving your thermal mass heat storage for sunlight. Jars of colored water or oil in the sunny windowsills, stone-slab or tile (even over carpet), stone or glass coffee-tables and curios, and other thermal mass additions can store a lot of heat while spreading it out at acceptable loads for an apartment floor. Insulating drapes or wall-hangings can help you trap that heat at night. Use shady / exterior walls for storage, e.g. wardrobes or enclosed book-cases, with insulation between furniture and wall.

I'd love to hear / see pictures from folks who have done some experimentation in this space. Especially if you've built a "lower-mass" mass heater. Brick cookstoves, ovens, and fireplace retrofits count too.

-Erica W

Erica, staright away, i notice something, you haven't talked about bells. They seem low mass enough to be taken into account.

Like Sandy Mathieu's recent work

http://blog.dragonheaters.com/6-dragon-burner-masonry-heater-using-chimney-flues-part-5-2/

Or Peter van den Berg inspired massakachel. May be not light enough yet, but could certainly be lightened to fit other spaces.

http://technologieforum.forumatic.com/viewtopic.php?f=19&t=27

I don't know much about the us. But over here, lots of flats and houses are made out of concrete or stone. And making the pipe run directly against a big inside supporting wall, and covering it with cob which is also stuck to the wall could lead to amazing thermal mass. Another option could be to make a second "bell", after the barrel. Which would be tall and flat. Think something the size of a matress, in which the gasses would go through, and still have convection movements; stuck against a brick wall.

Being timber framer/roofer, another option springs to mind; spread the load. two or three big wooden beams or even RSJ linked somehow by spacers and you build your mass on that, using the beams as part of the mass. But there's the scorching problem. RSJs might be better at the scorching isue, but the problem is expansion which should be taken into account. Spreading the load over 20' or even 40' feet could be possible. If the mass is concentrated on some part of this, the ends of the beams could be hiden transforming theses into a little platform, with wood flooring or something.

People with hearths should have no problem fitting whatever rocket they want, and using the wall mass. And usual fireplaces should not be that dificult either.

One thing, for example, i'm going astray from the barrels. They are usefull, but i want square "heat exchangers" so i can pile up bricks of concrete pavers or whatever around. I mean dry stacking some standardized massonry elements. This would enable to have slower heat and using a bigger rocket into a smaller space. Charging the following mass faster.

HTH.

Max.

Hello Erica, I don't have a RMH, but have a small standard Century S244 secondary reburn woodstove for my 1100 sf 2 story house. Century says this stove is good for 250 to 1000 sf. EPA rated 21,000 Btu hr, the mfg says 40,000 btu.

Kiko Denzers hat inspired me to add mass in the form of SS pots of water on top and around the sides of the stove. I have about 55 gallons of thermal mass around the stove.
- I flip the lids so they are flat, drill 4 holes and drop screws in so the lid doesn't pop out when I double stack the pots (learned lesson, lucky water was cool)
- Caution, no guarentee this is childproof
- the SS pots were low cost, $8 to $14, made in India and most handle rivets developed leaks. Will try JB weld high heat epoxy to get water capacity back up.
- later I added 4 IMUSA alum 8 gal tamale steamers. $21 each. These are not in intimate contact with the stove sidewalls due to a lip on stove top.
- the lids lessen humidity, the screw holes are the relief valve
- I also load 3 - 4 lbs of wood pellets in bottom of stove to max burn time in this small stove. Logs on top. I cut 1.5" x 36" ss square drilled tubing into 5 pieces about7" long as a "wood pellet basket" so the pellets get O2 to combust.

I have 2 small fans blowing on flue pipe trying to catch exhaust waste heat.

Thinking about adding:
- add on catalytic combustor
- then a few feet above that, the Magic Heat reclaimer.
- 2 cast iron hearth backs on the sides. About 20" x 20" x 1". Cost $99 each. (maybe 2 more for back and bottom of stove)
-concerns about added weight of water on the tack welded stove legs makes me want to add some stacked brick under legs.

This helped me get thru last winter in CT. I was able to burn hotter, and the mass let me sleep longer

Bill

I am not really clear on where those pots of water are going, but they sound like they are surrounding the firebox.

If so, you run the risk of cooling the combustion, increasing emissions, and increasing the amount of wood you need to burn. Combustion temperature must be VERY high 1200F at least to make use of the gases released. 50-60% of the BTUs are in the gases. If you cool the combustion zone, done by extracting heat from the combustion zone, rather than afterwords, you will quickly increase the amount of wood required because you are sending it up half the energy up the chimney, instead of burning it. This is one of the big ways rocket heaters are more efficient, they do not attempt to extract heat until the gases have gone through 2 insulated combustion zones.

It would be better to put all your heat capture after your firebox.

Thanks Sandy, I'll have to post a photo of the stove. 8 stacked pots sit on top of the stove for a total of 23 gallons. I was hoping since this is after the secondary reburn it wasn't cooling the burn?

Their are 16 gallons on each side but there is a 1" gap at the closest part of the round. I have a stovetop thermometer and I aim for 550 - 600f on initial burn.

I hope I'm not hijacking Erica's thread.

How about if the mass was contained within the bell/heat exchanger? With channels for the gases to flow through?
Yes you would have to be careful not to bottleneck the flow.

Sandy, here are photos of my stove. I keep water in pots as cooling thermal mass in the summer. (not all pots shown- been steaming crabs)
My wife calls it the Nacatamale kitchen

Sandy, Erica and all, since the pots on top are after the secondary burn (and side pots not in actual contact with stove) is too much heat being taken off the stove?
- using the wood pellets, kindling and logs I quickly get up to 600 f (sometimes have had trouble keeping it less than 700 if too many pellets added)
-are my ideas of adding 20" x 20" cast iron panels in intimate contact with stove sidewalls valid (my thought is their is a great deal of heat stratification in the water pots and a max temp of 212f with a phase change. Hoping the iron will disperse the heat better

- along those lines, whats the difference between a cheap stove and good stove? More cast iron, thicker steel, no?

- will adding an add-on catalytic converter work. Woodsman plus has one that is added on. After the stovetop. My thought is 400 f is kicked up to 800 f and i can extract that extra heat by fans on flue or Magic heat reclaimer higher up (plus less emissions)

-my understanding is that waters thermal mass is 4x > than concrete or cob by weight.
So my 55 gallons of water = 450 lb~=2000 lb concrete/cob mass?
Thanks again for the advice

Hello, adding a photo of my wood pellet "basket" steel 1.5" x 1.5" perforated square tubing. This allows me to put up to 5 lb of wood pellets on the bottom of my firebox. Then a hotter, longer fire stores heat in 450 lb of water. The pots cost ~ $190. The 36" tubing ~ $28.

Also kicking around the idea of wrapping the flue with copper wool to increase the surface area that the fans can extract heat from. (don't use steel wool which oxidized can ignite at stove temps)

Sandy,
Your advice "it would be better to put all your heat capture after the firebox" has crystalized the idea that my next investment in optimizing my standard stove will be the retrofit catylitic combustor then externally wrapping the flue with 5 lbs of 4" copper mesh. (sold for pest control or alcohol distillation). Fans should take off more heat with more surface area.

Also brainstorming on having a slot just under the catalytic converter where I can insert an electric firestarter to preheat the catalytic converter. (need to make sure no gases can escape when slot closed)
Hope this will kick the Cat. into gear sooner and as a plus clean emissions.

Bill

Bill McGee wrote:Sandy, here are photos of my stove. I keep water in pots as cooling thermal mass in the summer. (not all pots shown- been steaming crabs)
My wife calls it the Nacatamale kitchen
...
-my understanding is that waters thermal mass is 4x > than concrete or cob by weight.
So my 55 gallons of water = 450 lb~=2000 lb concrete/cob mass?
Thanks again for the advice

Plus, you have enough spare water on hand for at least the first week of the Apocalypse

I've seen similar thermal mass additions with rocks or brick hearths, but I bet the water works better.

-Erica

Satamax Antone wrote:Erica, staright away, i notice something, you haven't talked about bells. They seem low mass enough to be taken into account.

Like Sandy Mathieu's recent work
http://blog.dragonheaters.com/6-dragon-burner-masonry-heater-using-chimney-flues-part-5-2/

Or Peter van den Berg inspired massakachel. May be not light enough yet, but could certainly be lightened to fit other spaces.
http://technologieforum.forumatic.com/viewtopic.php?f=19&t=27

I don't know much about the us. But over here, lots of flats and houses are made out of concrete or stone. And making the pipe run directly against a big inside supporting wall, and covering it with cob which is also stuck to the wall could lead to amazing thermal mass. Another option could be to make a second "bell", after the barrel. Which would be tall and flat. Think something the size of a matress, in which the gasses would go through, and still have convection movements; stuck against a brick wall.

Being timber framer/roofer, another option springs to mind; spread the load. two or three big wooden beams or even RSJ linked somehow by spacers and you build your mass on that, using the beams as part of the mass. But there's the scorching problem. RSJs might be better at the scorching isue, but the problem is expansion which should be taken into account. Spreading the load over 20' or even 40' feet could be possible. If the mass is concentrated on some part of this, the ends of the beams could be hiden transforming theses into a little platform, with wood flooring or something.

People with hearths should have no problem fitting whatever rocket they want, and using the wall mass. And usual fireplaces should not be that dificult either.

One thing, for example, i'm going astray from the barrels. They are usefull, but i want square "heat exchangers" so i can pile up bricks of concrete pavers or whatever around. I mean dry stacking some standardized massonry elements. This would enable to have slower heat and using a bigger rocket into a smaller space. Charging the following mass faster.

HTH.

Max.

Spreading the load could help, but I'd still want some evidence that the building could handle the additional mass.

Bells are an example of a different masonry heater design that might be lower-mass. I have seen some reports that they are compatible with rocket mass heater fireboxes, but haven't had time to build and study them for in-situ problem solving. They would be a significant enough design change that I'd want to understand more about them, like how they would interact with the exit chimney, and how vulnerable they would be to leaking, and what surface temperatures to expect.

Barrels: The radiant barrel sheds heat faster than masonry, which turns out to be somewhat critical to downdraft in this part of the stove. Many folks would enjoy seeing an all-masonry version, or tile, but recognize that it will be far more dependent on exit chimney draft than the current designs.
The quick radiant heat from the barrel also seems to please the American market where we are accustomed to quick-response woodstoves, and often don't think about the heater until we are cold. We have done some experiments with heat-shielding or layers of material over the barrel, which works OK as long as there is air flow between. We've also seen all-brick stoves that claim to be rocket heaters, but not much detail about how far they can push through channels or what kind of exit chimney is needed to ensure enough draft. I personally might call them a variation of the 'contraflow stove' principles rather than the rocket mass heaters, as the one I have in mind seems to lack insulation too.

Ianto's rocket mass heaters draft even with a horizontal exit, which is not a good idea in some buildings, but shows how effective the updraft/downdraft thermosiphon action of the heat riser and barrel can be.

-Erica

Erica, re: "soup kitchen stove"
We did fine during 2 weeklong power outages last winter. I'd carry a pot of water upstairs, mix it in a 5 gal with cool water and use a bowl to shower. Also cooked on the stovetop.

Another water for thermal mass idea I'm kicking around is replacing the kitchen table with a movable hot tub. "Spa in a box" (cost $850) is 280 gal (~2300 lbs of water) has an electric heater that heats to 104 f. Thinking about a 3 season rotation.
-winter (Nov-Mar) move hot tub to walkout basement where I have worries about pipes freezing. Used supplemental electric heat there last winter as well as the cast iron 1956 Arcoliner boiler (tankless coil hot water use only) Empty and water lawn.

Sping- Apr-May, hot tub outside on deck

Summer- Jun-Aug AC cooling. Don't use as hot tub, just as passive cooling mass. Put plywood over top (73" dia.), add table cloth.

Downsides:
- underestimating work involved in emptying and moving this
- NOT A LOW MASS SOLUTION, need to add lolly columns in basement to support it when in kitchen?
- pump heater warrantee is 1 year. Reading reviews they do burn out at a cost of $400.
(Maybe I can build a solar heater to assist)
- driving wife insane if I add this to kitchen (deck/basement she wouldn't mind
- can the emptied water be used to water lawn? Are there non-toxic spa chemicals? What if no chemicals were added in last 3 weeks before emptying?
Just brainstorming here. I'll post this as a seperate post in the future.
Bill

Erica, , have you read this?

http://www.stove.ru/index.php?lng=1&rs=16.

Bells don't impede much with the flow. THere's friction from the exit of the stove to the bell, in some cases, there's only the heat riser exiting directly in the bell, and from the bell to the vertical stack. Bells rely on stratification, hotter gasses go up, cooler ones goes down, but thoses movement are powered by heat and gravity, so there's isn't much friction.

On the leakage side, well, i'm not too sure either. That's why i'd like a metal bell surounded by removeable mass, so, when you move, you can move the thing too. But Peter van den Berg said that in his prototypes, he always had a lesser presure in the bells, barrels etc than inside the room. Tho, that might be due to the chimney stack of his garage/workshop.

Comming back on, the matress size bell. That would be realy intresting, against a wall, in a massonry house. Very light. Can be quick heat on one side if left uncovered, or even for more storage, one of thoses brick fascia/veneer with mesh could be atached to it. It's always complicated to have someone make a single piece of metalwork, but can be done. Or better, can be found. Over here, there's a lot of tanks for tractor fuel or home heating fuel which are rectangular, ranging from 500 liters, to 1500 which could be used as bells for low mass, and surounded/covered by some light mass. Like pavers, bricks.

http://www.leboncoin.fr/annonces/offres/provence_alpes_cote_d_azur/occasions/?f=a&th=1&q=cuve+fuel+&it=1

I'm pretty sure they do exist on your side of the atlantic.

Lets take this one in example. http://www.leboncoin.fr/bricolage/408693233.htm?ca=21_s

Cut the legs, rest it on the floor and against a wall.

Sides take 5x23 bricks each that's 230 bricks
Front takes 161 bricks aproximately.

and the top would take about 77.

Let say for ease of dry fitting we use perforated bricks (with rebar shoved through, may be) I've checked a french site, they say for their perf bricks, 1.93 kg, that's about 4.25 pounds each.

So, 468 bricks x 4.25, that's 1989 pounds over 19ish square feet. That's still a bit heavy thought! Over here, residential building is rated 300kg per square metre safe working load, and comercial is 600. So that's 660 pounds per 10,76ft² for residential, and 1320 pounds for the same surface in comercial buildings.

It would be fine in a comercial building, but not in a house on joists here. Don't know about your side of the pond.

Satamax, you mentioned spreading the load. Would a 3/4"x4'x8' plywood pad work (32 sf vs 19sf). Any possibility to share the load with the wall and ceiling joists?

Satamax Antone wrote:Erica, staright away, i notice something, you haven't talked about bells. They seem low mass enough to be taken into account.

You can make a really cheap, light, and easy bell out of a barrel stove extra barrel kit (like this: http://www.amazon.com/Vogelzang-Barrel-Adapter-Model-BK50E/dp/B000N3WAHU/ref=sr_1_3?ie=UTF8&qid=1379777439&sr=8-3&keywords=barrel+stove+kit)

Simply extend the exhaust flue pipe down into the barrel. The barrel stove would be WAY too much heat for any small space, but the bell could be added to any smaller stove w/ 6' pipe if you built your own stand. Or you could downsize the idea to fit the space with whatever material you could source.

Bill McGee wrote:Satamax, you mentioned spreading the load. Would a 3/4"x4'x8' plywood pad work (32 sf vs 19sf). Any possibility to share the load with the wall and ceiling joists?

Bill, about your pad, well, it should spread the load somewhat, tho, not much, not being thick enough. I don't know the numbers for ply eithyer.

What is your house made of?

If you can give me on center spread of your joists, span, what type of flooring there's on top and the dimensions of the floor joists, i could do a quick calc. If you are thinking of using a fuel tank as i sugested, it could atached to the wall, so it would at least bear it's own weight and the one of the bricks on top of it. You could even add a lip on the bottom, welded, so it would support the side bricks. And share the load between the wall and floor. There's another thing, if the "mass" is close to the supported end of joists, they can bear more than in the middle. And the numbers given above are for static load, spread. So every square metre of floor is able to whistand the load, even if all of theses are loaded.

But if you spread the load on 8'x4, a "slab" of plywood 4 inch thick, all glued together would most certainly hold it nicely.

R Scott.

There's plenty of options.

Hard bit is to make a removeable mass around a barrel.

There's len's way.

https://permies.com/t/10653/wood-burning-stoves/portable-RMH

Cob way too.

Myself, i'd tend to do it in a brick lattice, if the barrel is vertical.

https://www.google.fr/search?q=brick+lattice&safe=off&rlz=1T4SAVJ_enFR550FR551&tbm=isch&tbo=u&source=univ&sa=X&ei=L8E9UpzuNe6z0QXguIHADg&ved=0CDQQsAQ&biw=1216&bih=535&dpr=1

Peter van den Berg does a double barrel on bell on top of each other.

http://www.youtube.com/watch?v=tpsGO9tY8rY

Which could be also covered somehow. Or half covered, that's the idea behind the brick lattice. But if you want more of a monolithic mass, you'd have to go either for square/rectangular metal container which is easy to cover with mass. Or go for a proper massonry bell.

You also have the Matthew Walker solution, the half barrel system.

http://donkey32.proboards.com/thread/560

and my take on this.

http://donkey32.proboards.com/thread/833/tube-incher-bell-volume




One i forgot to show you Erica.

Thank you Satamax for that pearl of info that 5 sheets of glued 3/4" plywood for a weight bearing "slab"

You sent me on an interesting trip to the basement. It's an old house, 75% 1850 with a 1960 addition.

Wood frame, granite stone foundation mostly (with concrete block additions).
All floor joists are 16" OC.
Sloped property with walkout garage/doors on south.
It's a 2 story plus basement listed at 1100 sf. The basement adds on 712 sf but is not living space now. It has a center chimney (looks like it was renlined with 1/2 steel) the chimney also serves as one of the support colums. I brought it from the family of the 96 year old owner 2 years ago. (she was still burning wood at 94, I'm using the same stove). All the mechanicals in the house are old and suspect, but I got a good price. It's a litttle garden of eden in the 'burbs on the outskirts of a dirty old, run down Connecticut city. (aren't they all)
FIL and I replaced the 60 amp service panel with 200, replaced all outlets, added GFIs, grounded all. Added 20' x 12" ceramic tile in south facing kitchen (with subfloor) so got thermal mass added on.

Back to the floor; 16" OC, Span is 26'. (first span 5' from foundation will be main weight bearing, then 7.5 feet between the other 2 spans) A menage of lumber but it looks solidly built. Half the house floor joists are 2" x 6" and the half I am adding thermal mass are real 3.5"x5"
-the 3 support beams spanning the joists are 7.5"x8" or 6"x6". There is a mix of RSJ (L beam 3/8"x4"x4") and individual 5/8" gage steel joist hangers. The span which will bear most weight has a 15"x37" concrete support column.
-the next span has 2 steel lollicolums plus 4x4" colums I added at base of stairs.
-the 3rd span has center chimney as support, 1 4x4" wood column and the wall of a 1/2 bath.
The prev. owners husband was facility manager at a local mfg, hence the steel. (I have great steel closet poles in all closets and some nice iron work outside- years ago working P/T in a large local family owned hardware store I asked the owner which hardware store is his main competitor (pre Home depot days) he answered "Electric Boat" it was amazing what came out of those guarded gates- not saying thats where this RSJ came from)

I am still not a convert to RMH's, I've never seen one in action. Like the apostle Thomas I will have to stick my fingers in Jesus' bloody wounds before I believe. You guy's say it's the roar that hooks you in, like a virgin heroin user.

I still have a road to travel with the conventional stove. I want to dial this in and maximize its heat output and clean it up. I am a reformed clamp'er and damper first getting religion with a Jotul, then a Tempwood smoke dragon (there were a few one night stands, but I don't remember there names, if I ever did.
I might be personaly responsible for 2% of all global warming...

Bill

So you say, the total span is 26', but there's beams at 5 then 7.5 then another one at 7.5 from the second, and you have about 6 left to get to the foundation on the other end of the joist.

Well, let's admit that the 7.5x8 is like a wall. I haven't understood all the posts that are under it.

But 16 oc, 3.5x5 should bear in that case aproximately 1.4 metric ton per square metre.

let say 3000lbs per ten square feet, if it's oak, and 2500 aproximately if it's pine. Tho, carefull if the wood is roten, that's no good.

Then again, the lengh of that beam is about 42' if i understand well. Divided by two, since there's a post in between the two ends.

If it was 8x8, it would bear 810kg aproximately. Remember, that's always safe working loads, about 5 times lower than where the wood would crack.

So you could load about 1.6 metric ton in the middle of that 21x5 surface. The closer to the foundation wall you get, the more it will be able to bear.

1.6 metric ton, or 3520 lbs, that's a pretty hefty massonry bell you could have.

Remember, i get this out of a 60's book. And a bit from my knowlege of timber framing. And advisers are not payers.

Thank you Satamax,
I hope I didn't burn out your calculator. (and sorry if my waxing poetic made for a more difficult translation)

Its good to know I have no excuse re: building a cob bench (or my hot tub kitchen table)

PS- years ago I lived in a large old farmhouse, that was believed to be the towns first fire dept.
It had interior walls that hung from long bars (bolts) through the 3 stories. I walked an architect friend thru the house who pointed them out to me. (I lived on the 3rd floor and he saw the nuts recessed in the floor). Boy did that house shake and rattle when the coal trucks hit a pot hole ridge in the road as they sped by.
In a borderline situation could suspending the thermal mass weight by hangers to the ceiling above help? (not my situation but maybe helpful to others)

Suspending part of the mass by tensioning cables or chains on the joists or rafters above could be done too. But if there's a bassement underneath, or even a crawl space, i'd rather reinforce the floor. Posts support huge amounts of load.