Hydronic heating switch for theoretical outdoor rocket boiler...

I am exploring how to build an outdoor rocket boiler to heat my home and provide DHW.
I am aware of the potential dangers, and I will take steps to remedy them.

Because of my situation, I am currently planning to use an inline pump to circulate water from the boiler to the storage.
I think that I have found a switch to do what I want:
Adjustable Snap Disc Auto Reset Limit Switch

Most boilers start pumping at 180F, this switch adjusts to close anywhere from 170f to 250F.
There are others that have a lower range, I might go with one of those, but mostly I'm wondering if Im on the right track in terms of when it will open and close.
I want a normally open switch that closes when the temperature past X and opens when the temperature lowers below X.
Will this switch do that?

the switch you linked to is an open on rise the one you want is a close on rise type... something like this one:  https://www.ebay.com/itm/Supco-AT022-Adjustable-Airflow-Thermostat-Fan-Control-Snap-Disc-Close-on-Rise/162992169963?epid=15012041727&hash=item25f31723eb:g:~6wAAOSwe7BWziOL:rk:2:pf:0
Snap disks work they are not that precise so start lower then you want just incase and tweak it up as you get used to it. Close on rise are usually used to turn on heating devices once they are warm enough. Open on rise are usually used to make sure heaters don't overheat.
Cheers,  David

Great catch,  apparently  Grangers search function is wonky,  tried it again with the same result.
Your link is not only the right item,  it's cheaper  too!
Thank you,  I'm an old grunt industrial electrician,  so I know more about climbing, digging, bending pipe and pulling wire than I do about control circuits, even simple ones.

Hey David,  is there a better,  as in more precise control that could be used in this application?

I'm not really answering your question William, but I'll explain how I've linked my Batch Box rocket water heater to an existing oil fired central heating system (hydronic) over here in the UK.

The BB heats a Clearview wrap around boiler from a normal box stove. It's rated at 45,000btu/hr. I've located the boiler around 10" above and to one side of the 5" heat risers exit. It's a 4 port boiler but only 2 ports are connected (lower left - cold water in, upper right - hot water out) The flow of water is caused by a simple thermo-syphon that then connects to a 'Neutralizer' Neutralizer - a multi-port beast that allows several heat sources to work together without interacting with each other. It therefore allows us to use either the BB, the oil CH boiler or both together. Thankfully I'm really only using the BB for most of the time, but it's handy to have the oil CH backup for when were away from the house.

I have a high limit stat and a low limit stat fitted to the feed and return pipes from the BB boiler and the whole combined system is open vented - ie: unpressurised. I made provision to fit a pump onto the hot feed from the boiler in case the BB boiled the water in the boiler, causing it to flash steam, but we have had no issues like that so far after two winters use. Certainly, in our case a simple thermo-syphon transfers the heat from the BB boiler without using a pump. We have used 1" copper pipes to connect things up.

If you run several batches a day it can provide most of our heating and hot water requirements on all but the coldest of days. Plus of course the heat from the bell and the glass door easily heat the room the BB is located in.

I think you are going about it wrong.

You should use a PLC to adjust a metering valve so that your water temp INSIDE your system is adjusted exactly for the temperature loss of your space, the ambient temperature, your returning water temperature, etc. You would get much better control that way.

I would think that would be much better for a rocket boiler as there would be a lot of temperature spikes which the PLC/metering valve is ideally suited to adjust for.

With hydronic heat, you should not have to get your water very hot. It depends on what you have for a substrate, but one of my houses utilizes water at 75-100 degrees to heat it. When your entire floor is a radiator, and you are heating the contents of the room and not the air itself, the temperature of the water running through your floor should be a lot less. If that is not the case, then the design is flawed because it is over-heating its water and controlling the set temperature by its zone valves which is NOT what a person wants for most efficiency. Why heat water above 100 degrees if you do not have too, just to have a zone valve shut off so that hot water sits there and starts cooling off?

As the air outside gets colder, the space losses heat faster, so the water temp circulating through the floor has to go up to compensate
As the air outside gets warmer, the space looses heat less, so the water temp circulating through the floor can adjust to it

The PLC does this by monitoring the outside temp every minute, then making changes to the metering valve taking into account what the returning loop temperature is so that a precise amount of hot water is injected for what the floor is losing (typically a 15 drop from entering the floor to exiting the floor)

All the rocket boiler has to do is make hot water (water temps between 100-150 degrees) for the metering valve to inject into the hydronic system. Honestly it does not care if this water is heated by compost, solar, tradional wood boiler, or a rocket boiler; as long as the water is between 100-150 degrees it can draw from it and effeciently heat the space.

All the thermostats in the room do is tell the PLC to come on. They also tell the zone valves in an over heat situation to shut down, but on a properly adjusted system that never happens because the PLC already has got a handle on that as we talked about earlier.

To make my system even more effecient, I wired the thermostats in sequence so that that it takes (2) of the three thermostats calling for heat to tell the system to come on, in that way, if the north side of the house calls for heat, but the south side is warm enough, only when the house averages out to call for heat, does it kick in. This allow my system to stay within a degree of what the thermoststat are set at. Keep in mind, I am doing this with water running through my heating loops that is between 75-100 degrees.

I like Taco products for what it is worth!

Is there a reason why you're planning to build the rocket boiler outdoors?

Great replies and questions.
First,  I think I mispoke(miswrote?).
I called this a hydronics system, but I am not running pipe under the floor to heat the space.
Rather,  I'm using the water to move and store heat.
The stored heat will be distributed via a heater core in the return air vent of the existing natural gas forced air furnace.
Less efficient,  I know but in keeping with the parameters of my project.

Speaking of which,  I'm planning on building outside and bringing the heat inside because my wife doesn't want a homemade heating device inside the walls of our home.
I ain't mad at her for that, it's a reasonable stance.
Hot water is hazardous, but not as bad as Flame and smoke.
Adding heat into the return air of the existing system gives me a means of distributing the heat,  with a minimal outlay of effort and materials.
The gas furnace will kick in as needed,  drawing air past a heater core.
The heater core will be above the storage tanks, so a  thermal siphon should work.
The boiler  would be located higher than the storage tanks,so I think a passive thermal siphon loop would only work to cool off the stored water while the boiler is cold.
Because of that, I plan on using a thermostatically controlled pump on that loop.
The boiler loop will pass through a small water heater tank located in the bell portion of the rocket mass heater.
It will share water with the storage tanks.
I would love to pass the DHW through these same tanks,  but boiler pressure release valves are set at 30psi, lower than DHW,  plus,  who wants to lose 1000s of gallons of water in the event of a blowout?
A water to water heat exchanger will have to do.
Storage tanks will be defunct water heaters, in series,because they come preinsulated,are modular, with ports,for almost free.

William: thanks for being so understanding, I was curious as to what I was missing because I was thinking, "Man, he is pretty good with this stuff, so why did he miss that." Now I understand; no hydronic heat, and using a heating core in the plenum of your existing furnace. I understand keeping things simple, yet not being 100% dependent upon fossil fuels. I even understand getting the fire outside instead of being in the house: Happy Wife, Happy Life, even if it means wife is happy by feeling fire-secure! :-)

My only concern with your plan might be that with the rapid heating of the main boiler loop, in conjunction with the rather slow transfer of heat via siphoning, might cause it to flash to steam and blow out the relief valves. Once in a blue moon when unicorns are grazing in the back pasture is no big deal, but if it happens every day, then it would be.

So I got thinking about this. What is the worst that could happen? You would constantly go into relief and have to rethink your plan down the road. My suggestion would be to try it; going heavy on the relief valves, making sure you have a high point vent, and be sure to have a makeup water inlet as well.

I'm rather pleased that you would be surprised at a gaff on my part.
I count you as an accomplished maker, so I'm glad you expect better of me!

The different rates of flow and therefor heat transfer are necessary if I am to store heat till it is needed.
The pumped loop is so the storage tanks can capture  BTUs as quickly as they are produced by a batch box rocket.
The thermal siphon exists so the forced air system can extract these BTUs as needed.
This line of reasoning leads me to conclude that 3 or 4 water heaters isn't enough storage.
I might in fact do the math but I'm pretty sure it will not be enough to make any significant impact on my heating bills.
A bigger tank would seem to be in order.

Build It Solar has a nice build:

It should be within my budget and skill level to build.
An in-line pump drawing water from the depths of the storage tank,would push the hottest water out of the top of the boiler tank.
The storage tank might make for a good bed platform, or seed starting bench.
A 4' x 8' x 2' tank would hold more than 470 gallons, and it would be great place to put The DHW heat exchanger.
Two 4' square 2" high tanks might be better for strength.
A defunct water heater, stripped of insulation and immersed in the storage tank would mean many gallons of preheated water.
I would want a line to the the city water supply , with a float valve,to ensure the storage tank was never dry, so adding the preheating loop wouldn't add much in the way of  pipe used.


Another design element troubles me.
To avoid the hazards of steam, my plan has been to keep the boiler tank out of the hottest exhaust.
Instead, I was going place the tank in a bell, and allow the exhaust to surround the tank.
The tank is roughly cylindrical and the poor surface area to volume ratio could hinder heat exchange.
Further, the boiler shed is is exactly the place we want to remove the heat from, so more time spent hanging out in the bell is a drag on performance.
I'm wondering if a small stainless steel tank located right over the riser might be a better choice,even if it means downsizing the batch box rocket.
At that position, the tank will always be exposed to the highest heat in the system, even if the fire is out, and smaller tank would have a better surface area to volume ratio.
But I will be courting boom-squish.
How many boiler pressure release valves could I practically employ, I wonder?
Would 1/2 black iron survive as supply and return lines to a tank in that position?
Could I adapt some stainless steel gas line to do the job?

One last musing for now.
Would a simple TLUD be a better choice for my heat source?
I haven't been able to get my 4 gallon stock pot TLUD to reliably run on anything but wood pellets, but boy does it run!
I suspect it's the regular size and dryness of the pellets that make them ideal.
To scale up and not pay for the privilege of burning biomass, I'm thinking pallets are my best bet.
Even old,out in the weather pallets burn pretty well.
A bundle of pallet wood vertical in a TLUD, might have the combination of regular shape  dryness to burn well.
Another thought, pallet wood strapped into a Swedish Torch configuration.
As always, the value of scavenged biomass is diminished by how much you must process it to use it.

6" Batch Box produces about77323 BTU/Hour

My house is old and located in a cold region, so according to this, it needs 60 BTU/Hour per square foot.

My house is 1452 square feet according to the county auditor.

That works out to 87120 BTU per hour.

If that is correct, I will never get ahead, even  assuming 100% efficiency it will take 1.12 hours of firing to provide even an hours worth of heating.

Lets try again with more nuanced , and lower numbers from here.

That site suggests 45 BTU/Hour for an older, less insulated house in my location.

That works out to 65340 BTU/Hour.

If correct, every 50 minutes  of firing a 6" batch box should give us and hour of heating.

Better but still meh.
This rocket boiler is only a 5 inch, and seems to achieve adequate results.

It is located inside,I've not found how often the boiler is fired, and it drives an actual hydronic system in a house of unknown size, all unknown factors.

I'm grasping at straws,trying to find out if building it is actually worth the effort.

I want it be because,duh, FIRE!!!, but I also have a responsibility to make sure my playtime pays off for the family.

I went through similar design process for a rain water capture system.

The conclusion I came to was"Reduce your Needs"

This could be the off grid mantra.

When you must do for your self, you find ways to do without.

I got a new(used) high efficiency cloths washer and a low flow toilet, and now my water bill is down 1/3rd to 1/2.

This makes the math on collecting rain water better, as I no longer need a tank the size of my house.

So how can I reduce my heating needs?

I have solid brick walls on the first floor of my house.

I have insulated the second floor, and the attic.

The attic could be insulated more, but I reason to believe that this would give diminishing returns.

I have 90 year old windows with 30 year old(?) storm windows.

My family(wife) has vetoed turning the thermostat any lower, though to be fair, it sits between 65-70 as it is.

So windows seem to be the low hanging fruit.

First floor windows are diy-ible.

I generally only work over 12' in the air on a wage paying job site, because of workmen's compensation, or the lack there off.

I'm the wage earner, if I die or get hurt doing something ,the family unit needs to get paid.

I think I will try repairing and sealing the existing windows before I replace anything.

I  will also look into EPA approved stoves.

If I can spend an hour a night, burning things fast and hot, capturing the heat in piles of stones or water, and never dampening down the stove to a smolder, I might be able to have my fun and help my family at the same time.

Willilam

Is the BTU output of the BB realistic? What temperatures over time occur at your "boiler"?

How much of that heat will make it into your medium, water?

How much of the heat in your medium at the "boiler" will make it into your house? There is big loss through piping and insulating piping is a significant effort and cost.

Acquiring and then moving heat around with a medium is a very demanding proposition, me thinks, w/out even considering the challenges of a high heat short duration energy source. It's a LOT easier to generate the heat pretty much where it's needed, ie. in the house and capture and store it in the house itself, ie. stone or other mass inside _where_ it is needed. You wife may have set you an insurmountable (for DIY) engineering challenge.

Finding a fit between an _appropriate_ technology and a particular problem w/in your purview can turn out to be THE problem. <g>

Addressing the parameters of the house could be the good bet.  Maybe you're familiar with this stuff, but for the record: You have heard of the "stack affect"? A house wants to be like a chimney, moving air from the bottom up and OUT the top. It's very powerful and it sends lots of heat up to the stars carried by air flowing out if it can find any leaks up there.  Pretty much all building scientists look at sealing leaks at the top of the house as the hands down single most effective step toward lowering heating costs. Then seal leaks _leading_ to the top of the house.  You say we can't close off the stairs... Well, likely true, but what about leaks through electrical outlets into your wall cavities? Switches? How about those stairs to the attic, the door at the top? Then, what about (cold) air coming _in_ at the bottom... The outside doors... And now we get to the leaky windows. Tape all around the moving parts of the windows (they won't move again until spring). Caulk around the window moldings; caulk along the baseboards, top and bottom. Go into the basement (unheated, right?) and plug those holes in the ceiling where pipes and wires go up. Tape the basement door if there is one leading out that's not going to get used until next summer. If it's an old house and you leave a bathroom window cracked open, you'll still have plenty of ACH - AirChange per Hour. Then at night pull the shades or close the curtains to reduce radiating your interior heat outdoors. Blocking radiation out has a lot bigger impact than most people realize - sit in a chair beside a tight window the is unshaded, then shade it with curtains or even with just a paper pull-down shade. I think you will find the difference easily noticeable.

Solutions w/in our reach with immediate payback.


Rufus

I agree that it is a wise decision of a homeowner to help tighten up their house for air infiltration, stop convection currents within their walls, and reducing the stacking effect, which is sometimes rather boring and unimaginative, but allows for the best bang for the buck. The best way to do that is to picture a home turned upside down, and then imagine it filled with water. Anywhere the water would leak out, do what you have to do to stop the water from leaking.

But beyond that, I disagree with some ideas proposed on here. First, while building an add-on (or also called supplimental) heating unit can be expensive, it has a lot of advantages too. It could be employed:

1) All heating season to help reduce fossil fuel consumption
2) Used during the "shoulder" seasons (Fall and Spring) to just heat the home without the use of fossil fuels
3) Used during the dead of winter exclusively to heat the home

Time will tell how and when William decides to use this heater.

But I wholely disagree that it would be ineffecient. Because water is 600 times more dense then air, by heating water, it also has a lot more heating ability when it eventually gets to where it is going. Today, with modern pumps and controls, we not only can do this, we can do so REALLY well. Add in high density insulation, and we can control precisely what we need effeciently.

But what is proposed here is nothing new, and has been used for a long, long time. In fact, on the US Navy Destroyers I built, heating units in the ductwork of the ship was how it was heated no matter how far north it sailed. The heating source is not electric granted, but a lot of commercial systems use boilers to heat water coils in plenums. It will be his greatest loss of effeciency, but that has already been established, and explained why it is being done this way. About the only novel thing about this build is that a rocket heater is being used outside to heat the water.

In some ways this is an ideal. The rocket heater has massive spikes of heating capacity and is no where near linear, yet that dense water will absorb it, then the holding tanks will release it into the plenum.

This is an easy project, but doing so on a tight budget is the challenging project.

Plenty of good stuff here.
I totally agree,  there will be losses and sealing the house more is a wider first step.
Plus,  the heater appears to be inadequate to the job of creating  a surplus of stored heat.
The BTU number came from the father of the batchbox RMH.
He might have refined it since,  but I think it's good enough to play with.

My other numbers above are from websites conventional heating, they might be bogus, or simply misleading for my purposes.
I'm struck by the anecdotal evidence of 6" batch rockets heating mass enough to warm a small house for hours with only a few 45 minute firings.
My thought experiment should come out closer to that same conclusion, especially since I purposely set aside any consideration of the extra losses at play here.
If your figuring tells you that something that has been done is impossible, you are probably  figuring wrong.

I conclude my numbers or methods are wrong.

I can't find the BTU rating on my current furnace right now, so that is a dead end.

Cheap EPA approved furnaces have efficiencies in the 75% range, which sticks in my craw,so that plan is out,  for now.

I've been distracted by tank design, especially since the knowledge can serve my reduced rainwater capture ambitions as well.
Riffing on existing design, I can see 2x4 reinforced plywood tanks lined with extruded polystyrene foam panels.
Sealing the edges of panels with KERDI-FIX,or some cheaper alternative could eliminate any need for a EPDM lining,which would be neat,  but limit heated water to 165F.

I want it be because,duh, FIRE!!!, but I also have a responsibility to make sure my playtime pays off for the family. ---   William Bronson

This is an excellent philosophy. I have known two guys who bought a race car and pretty much bankrupted the family with their playtime.

Your gas hot air furnace is most likely in the 130,000 BTU size range for the size of house you listed. Keep in mind heating appliances are sized for the highest expected loads (called temperature degree days) too. There is a LOT of fudge factor built in, but must confess. saying it is a 130,000 BTU unit is only a guess on my part.

I also confess, with more than a little humility, that I know little about Rocket Mass Heaters. I know conventional systems, and solid heating systems like pellet, firewood and coal quite well, but not Rocket Heaters. I do grasp the concept of them, and their efficiency does not escape me, I am just saying exact construction of them I m not well versed in.

But ultimately I see that as the problem. Conventional system people scoff at the rocket mass heater design, and rocket mass heater lovers scoff at conventional heating systems. Myself I think there are times when marrying the two would work well.

In my experience though, what sinks a homemade project is trying to do too much. In other words, off the shelf parts save the day. In your case, a great storage tank might be a #2 oil furnance tank which holds 275 gallons. That can be cleaned out, so a used one can be had for cheap (at least in Maine anyway). A 300 gallon IBC used tote would work well too. The problem with either one is the pressure they can handle. I think a #2 fuel oil tank is rated for8 PSI and boiler relief valves are set for 12 PSI. I am not sure about IBC totes.

Building with what's on hand will keep financial risk at bay.
If I build a failed heater instead of watching TV,  wasted labor won't be an issue either.

William Bronson wrote: Building with what's on hand will keep financial risk at bay.
If I build a failed heater instead of watching TV,  wasted labor won't be an issue either.

I like to think things through myself, and do a little bit of planning, but at some point it can become "paralysis by analysis" and that is not good either. Still, if I am thinking about ways to make life better and not idly watching TV, or spending gobs of money on some professional sports team whos fate is determined game by game, so be it.

Emotion: it has its place. The arts, writing poetry. Paintings and drawings...all great stuff.
Theology: It is great to be utterly truthful

But what good is any one of them by itself?

I can write the most flowery, loving, romantic poem to my wife about her big green eyes, and her wonderfully flowing blonde hair, but it would be all for not. Not because it is not sincere, and I have the greatest of intentions, but because my wife has blue eyes and is a brunette!! I have to be truthful (theologically right) in order for me to be effective. But most of all, I have to act, for what good would it be if I wrote a lovely, romantic poem that truthfully depicted her in every truthful detail (theologically sound), if I never gave it to her?

How can anyone have a testimonial of how something works, if they never get to a point where it can be tested?

I am a doer too, and pretty proud of that.

Totally get the doing.
I am actually addicted by anxiety to the point I choose to medicate it.
Action is a balm for me.
When I  can't face what needs to be dine,  I wash dishes.
Having accomplished that, I am reminded that I  am able.

For example, our house bunny just died, like a few hours ago.
We are having a bonfire tonight,  tomorrow  we dig.
I will help my daughter make a headstone for the bunny that was her first pet.
Love shown through action.
My affliction will hopefully  not become hers.

I am steering back towards starting with defunct water heaters as my heat storage.
They are on hand, after all.
I love IBC totes, and I  have a good source for them, but previous experience shows they won't fit in my basement!
I'm familiar with aquaponics projects that use deduct freezers as tanks.
I would love to try that.
I've used window screen stapled to wood and plastered with cement to make water impervious counters, and I always have wondered if that technique could make decent water tank.
There would be considerable pressure against it,  but strait Portland  cement has been used to waterproof concrete tanks before.
I plan on trying a bunch if things in pursuit of a cheap, easy to build/aquire tank.




I love making things, and focusing on self sufficiency projects replaced my juvenile pursuits of cosplay and other escapism.
Not that I have disdane for those things,  just that I  would rather build a sputtering woodboiler IRL,  than forge a sword in a game,  or even IRL.

Travis hit it right on: The major failure point in DIY is taking on too much at once. Eg. the hot water tanks (ready made, sorta) do you better than home made tanks because you have so much else that it's important so that it's better to avoid sinking time into something when you can find adequate parts already made. My thoughts on your options really centered on the "too much to do" problem, not the ability to (eventually) implement something. Effective, functional hydronic systems come with HUGE mountains of nitty gritty stuff the must work _well_ if the whole thing is to have a chance to actually help others. That mountain of necessary, required detail is the problem, not the theory of the plan.

Other stuff:

Cement can be used to parge and seal, but not if the structure moves at all. Many materials bend under normal loads and that will put paid to cement parging if water tightness matters.

Sorry, I don't remember if your existing heater is oil fired or natural gas or LPG.  You can measure the BTU input to your existing boiler if it's gas fired and you have metered gas.  Shut off other loads and mark the meter, then fire the boiler and after, say, 2 , or maybe 5, minutes, mark the meter again and do the math. Look up the BTU value of a cubic foot of gas in your area (which most meters measure), then multiply by 60/(minutes measured).

Travis again hit right on saying that most retail heaters in the last 100 years are sized large for the needs of the building. If you seal and insulate the house effectively, you might hope to use less than 1/2 of the BTU your heater is rated at to maintain 65-70 F.  90% or more of the time. However, the benefits will not be quite as easy to realize as you could hope because the heater you have will still produce the extra heat and because your house needs less heat to maintain temperatures, the heater will tend to short cycle. It will quickly make things too hot, then shut off until they get cold again, then give a burst of (too much) heat...  Short cycling is good for neither the people nor the heater. Using the large heat output to warm a large mass, like several hundred gallons of water, is one way to ameliorate this type or problem. It does require sensors, controls and pumps. More complicated detail.

But reducing your heat load is definitely a good thing and gives you solid progress to work with.

Regards,
Rufus

Oh, and "washing dishes". Done that. Worked well for me, too. <g>

I just learned about the trouble with oversized furnaces as I researched needed BTU's.
Tragic to think an improved envelope  could reduce comfort.
I wonder if thermal mass in or along path of the heated air would work as it does in in a RMH, evening out the delivery of heat.
Nothing to worry about until I get better sealing done.
Im thinking about sealing the window frames to the sash with a removable caulk.
The storm windows are so loose fitting I'm not sure if they help at all.
I really dislike dealing with plastic over windows but it could help a lot.
If only XPS foam panels  were translucent.
I might use them anyway, in windows that get little light anyway.

The BTU trick is awesome!
I think I'll try it,  get some peace of mind.


Perhaps due to the insulated second floor and ceiling, and solid plaster over brick first floor, a comfortable first floor usually means an over heated second floor at my house.
No return air ducts on the second floor probably contributes to this problem.

There's some interesting comments being posted on here.

Just to re-iterate what I've mentioned before -

I have linked a combined Batch Box rocket mass heater/water into an existing 'conventional' oil fired central heating hydronics system, and it works...

The BB rocket is located inside the house and provides mass heating storage for the room it's located in (and to some extent, adjoining rooms) as well as hot water.

The boiler I use with the BB is rated at 45,000btu/hr.

The boiler is located around 10" above my 5" heat riser and it doesn't flash steam.

The boiler thermo-syphons into the central heating system (via a 'Neutralizer' multiport device) without a pump.

The whole water system side is open vented - in the event of a power failure there is no pressure build up and excess heat is soaked up by a gravity fed 'heat leak' radiator.

Mine is not an ideal system. If I had the finances and the time I would build perhaps an 8" BB Rocket to drive a large boiler that would thermo-syphon via large diameter piping to a 2,000 litre (or larger) highly insulated thermal store. The BB Boiler would be on an independant open vented water coil loop that would only require a small volume of water. The water in the thermal store would store this heat and domestic hot water and the central heating would be fed from this indirectly - that is, these systems would be in their own enclosed pipe loops. The water in the store would just exchange the heat into them. (Tim Barker has done something similar with a domestic hot water/shower rocket)

It's nothing new. A lot of mainland European countries already use this type of arrangement and have done successfully for many years. The difference until now is that most of the existing systems use pellet or wood gassification boilers to heat the stores which are very expensive and relatively complicated. They rely on a lot of electronics, sensors, forced air fans, etc to ensure they function and the combustion is correct.

What I love about the BB Rocket is its simplicity and its ability to keep working in the event of a power outage. It doesn't need sensors, fans or valves - just dry wood and a bit of manual attention now and then. I really think that a BB rocket would be in it's element in this application. The large volume of water in the thermal store is ideal to 'smooth out' the btu output from a BB and store that heat for many hours. Maybe one day...

Without question there are some hurdles to all this, with the loss of power being a problem in a power outage being one of them. That could set up the system to flash to steam if the rocket stove was just charged with wood and the power went out. Another problem would be freezing up since this is an outside rocket heater. I just do not see a pump somewhere in the system though.

A person could have a back-up generator, or glycol used in the boiler water. That instantly makes the whole system lose 10% efficiency, not to mention a pretty high initial cost, but it would keep the system from freezing up. The backup generator would just allow water to be back-fed through the system, the normal forced hot air heating appliance heating the water in  the plenum and going back to keep everything from freezing until the power could be restored.

William mentions city water, so I am assuming it does not happen a lot where he lives, but it has to be guarded for.

Travis, I was worried about the flash steam possibilities too. That is why, when my system was piped up by our plumber, I made provision to easily retro fit a pump on the hot water flow from the boiler if needed.

My relatively small boiler has a capacity of only 28 litres or so. In nearly two winters of operation there has been no evidence of flash steam generation or 'kettling' - the simple thermo-syphoning system has worked unassisted.

I have a generator (we're out in the wilds of Wales and we sometimes loose power in stormy weather) but the electrically powered central heating pump only operates on the radiator circuit after the water from the BB has been injected into the hot water system. If the power fails, the thermo syphom from the BB keeps working, circulates hot water and prevents an overheat situation.

It sounds like you have what I have then, a metering valve which is kind of misleading because it is just a variable speed circulating pump that gets its input from the PLC.

The fact that circulating pumps are not check valves can be good and bad, depending on the circumstance. In a thermo-siphon situation, they are indeed a plus. My system is designed to be effecient, it happens to have only a propane boiler on it for the moment, but can accept anything. The boiler is the dumb part, the system itself just needs hot water in the main boiler loop to be between 100-150 degrees. It does not matter if compost heap, an outside wood boiler, solar, or a rocket stove heats the water, it just needs 100-150 water all the time to tap into.

The flow control valves in my flooring is where the real balancing act comes into play. Because of varying lengths of pex embedded in my concrete, I had to control the rate of flow so that the water exiting the loops was 15 degrees less then what it was when it was entered. This is what is called Delta T. 15 degrees is optimal. All that means is my loops are dumping the optimal amount of heat into my concrete slab floor without shocking the boiler system. So then my metering valve just takes enough of that hot water in the main boiler loop at 100-150 degrees, and brings the loop temperature back up by 15 degrees.

The Delta T never changes, which is a temperature differential.

What the PLC does is change the temperature running through the loops in the floor to match the temperature outside.

In Williams case, because he is working with hydronic to air in a plenum, he MUST figure out what the ideal Delta T will be. This is not theoretical high tech mumbo-jumbo, it is real world effeciency. He can easily do that through a partially closed 1/4 turn valve instead of a flow control valve, but will need to slow the water down so as the air is blown throgh the coil in the plenum, he is extracting the proper amount of heat. It is as simple as this: if the water is circulating too fast, the exchange will not happen. But if the water flowing through the exchanger is too slow, it will chill the water and shock the rocket heater when it returns.

Here is my system. The middle circulator looking thing is the mettering pump, and the (3) clock face looking things are temperture guages that tell me what the reterning temps are coming from my (3) zone manifolds called Delta T's. The PLC is actually a tiny retangle just under the black boiler and to the left of the gray expansion tank. (The box without the cover on it is my relay contoller which controls my zone valves.

William

> storm windows loose...

Even so, they help a lot. But if you want to tape around the storm window edge you can seal them pretty well. The downside is either getting the tape off in the spring, or, paradoxically, getting the tape to stay on through very cold weather. And, of course, not being able to open the storm windows should you want a few hours ventilation. Don't know what Ohio gets for winter.

If you have old wooden double hung windows and if you are moderately skilled with wood and paint you can improve their seal. It involves removing the sashes and installing either plastic or copper weather stripping along the edge - one type for the sides and different types for the top and bottom. However, it _much_ easier if you have the proper tools, either a small router or an old rabbet plane. If you use staples with the weather strip, it is more than just worth it to use either stainless steel or monel (if you can find them) staples. Then you put it back together and repaint where you messed up the old paint around the window. There are a lot of good tutorials on the net about rebuilding double hung windows.

Judging from my own experience, one window the first time will take you about 10-16 hours. It gets much faster after you burn through the usual screw-ups; figure two days,  provided  you have a good work table, and ways to hold the sash while you work on it. If you go to the trouble of removing the sashes, it's a good idea to reglaze and paint the outside, too.


Rufus