Hello!
Has anyone had any experience installing/using wood stoves with back boilers?

Like these: http://www.stovesonline.co.uk/wood_burning_stoves/Aquatherm-Eco-insert-boiler-stoves.html

Can these help run radiant tubing? Can I couple this with a SHW and Geothermal heating system? Would I even want to? I would love some information from someone that has installed one of these over here. (in N.A.) Thanks!

I have a Stratford EcoBoiler http://eco-boiler.com/ in my garage but I am about a year away from installing it in a passive solar house (now under construction!) I bought it on  e-bay in the UK. Paid $600 to Pilot Air to fly it from Manchester to Philly.
As a fellow pioneer, you will be facing a number of hurdles, including a small army of skeptics who may be less appalled if you wanted a nuclear reactor in your living room. Never mind that these stoves are commonplace in Europe. The hurdles:
1. The stoves are not EPA certified. Your code official can tell you if this is a problem in your part of the world.
2.  Your insurance company may require UL certification, which is also lacking here.
3. You'll need an open minded installer, or a very old one. These stoves are vented, meaning that they need an expansion tank and are more susceptible to corrosion. The U.S. HVAC industry switched to pressurized boilers long ago, and are accustomed to safety features, like automatic damping and quenchers, that aren't usually found on wood stoves. (My eco-boiler has automatic damping and rust control.) Your installer will have to accept that the Europeans have developed some sophisticated systems from what he would consider old technology. Show him this for starters.



(The Honeywell overheat valve operates without electricity and uses city water (mains) to cool the stove in an emergency. )
You can add solar hot water and any number of heat sources to the heat bank, and can use it for an equal diverse number of purposes. http://heatweb.com/Wood/Wood%20and%20Heat%20Banks.pdf
4. Automation is complicated but not impossible. http://www.stsscoinc.com/Products_EMC.aspx  In my use, I am treating my Eco-Boiler and a 1000-sf radiant concrete slab as if it were a masonry heater, with the burden on me to know when to fire it up and for how long.
5. An experienced operator must be in attendance, automated system or otherwise. Judging by accounts in UK stove forums, allowing a back boiler to boil is a clanging, hammering horror. Think small stove and big tank.     

Thanks for the great info!

I am looking to run this as a supplement to solar heating & hot water heating. I live in Vermont and it can get pretty cold up here. My thought was instead of a regular fireplace in my superinsulated new home why not install one of these, and on the coldest nights, fire them up to help the heat load and for some ambiance. Is this an appropriate use? My architect said my home should only require 20MMBTU per year to heat, which is equal to a cord of wood. I was thinking about running this with solar and using an air to air mini split system run inline with my ERV ducts to provide emergency backup heat and A/C in the summer. I might go with a geothermal system as well to supplement the system but feel that this might be overkill and a waste of money. What else are you using for heat in your setup? Is there anything else I should think about? How can I find a qualified installer? Thanks for the help!

Graham

ps How would I learn to operate effectively to avoid problems? (boiling, etc.)

"5. An experienced operator must be in attendance, automated system or otherwise. Judging by accounts in UK stove forums, allowing a back boiler to boil is a clanging, hammering horror. Think small stove and big tank. "


and this would be why a "small army of skeptics" would say this is a bad idea. Sooner or later, you might not be in full faculty. You might sell the house. You might just be an idiot. In any of those cases, the risks you are talking about are severe, disfiguring, expensive, and possibly fatal.

You might be willing to cowboy, but please don't encourage others to take those kinds of risks. heat exchangers embedded in enough mass to prevent boiling is one thing. tacked on to a relatively low mass wood stove is just dumb, plain and simple.

Funny, I have never thought of the Brits as a cowboy nation....
Let's examine this time bomb of mine in its nornal use. It is pretty much the classic marriage of passive solar and masonry heater except that my masonry is a thousand square feet of radiant slab. Raising it by 10 degrees will require about 100,000 btu. I'll also have 160 gallon reverse indirect tank to start. Raising it by 50 degrees requires 64,000 btu. My stove will put about 25,000 btu/hr into water for six hours at full throttle. Do the math.
Not that it matters. The stove has an automatic damper that reduces output to match demand, so the penalty for a mistake on my part is merely more soot in the stove pipe and a bigger particulate release. To handle a power outage, its manufacturer requires a heat dump radiator equal to the stove's output at idle. (DPS' tap water approach is cleverer.) I can set the stove at "idle" if the damper hasn't closed.
In the typical, riskier installation in England, Brits add stoves without automatic damping to often ancient radiator systems. Yet the original Nanny State does nothing. Why is that?
Also, how you get from the boil in my account, which was harmless if terrifying in what I read, to the implied fatal and disfiguring boom in yours, assuming an experienced operator in attendance? I didn't oversell these stoves, except in your definition of anything that suggests it can be done and is done by rational people. I treated the idiot factor offhandedly because I don't expect to find idiots here. Do you?
But if propaganda is cool, then shame on you, NRT Bob, for advocating household equipment producing an odorless, tasteless, colorless gas THAT CAN KILL YOU IN YOUR SLEEP.

Your wood boiler in the living room is NOT the same thing as the heat exchanger "inserts" people just throw into other wood boilers that are not designed for this kind of operation. It doesn't serve anyone to blur that line: the inserts have almost none of the safety features you describe even mentioned in their literature. They operate with an uncontrolled burn in a low mass situation every single time they fire, relying only on a pressure relief valve or two for safety. Not exactly what I would call bulletproof. That is what the original poster was asking about.

Your unit appears to be designed more like a real wood boiler. That's great, and it includes a few safety features that go a long way to helping things out. But that's not common in this class of product. So forgive my ignorance regarding the particular boiler you have. That said, I would NOT assume an experienced operator is in attendance. That would be nice, but if that is a requirement for safe operation, then the equipment is not suitable for installation in a residential home, period. Not unless you're going to rip it out when you die or sell the place. I'm not sure why they would require that if the automatic damper and gravity recirc heat dump were adequate to guarantee safety, are you? Seems a little CYA to me.

Flashing to steam in a pressurized system is always an explosive risk. It may not actually explode if the whole system can resist the pressures involved, but it's a pretty major repeated strain to put a system under that it wasn't really intending to withstand, and it will weaken the system. Maybe if you want to go back to quarter inch thick iron pipes and massive ancient radiators I'd be less concerned about it, but modern copper piping would be quite another story. I've seen it develop pinhole leaks in much less strenuous circumstances then you describe. The fact that it's not a leading cause of death in britain doesn't concern me much, it's a pretty serious risk I would never suggest to anyone. If this system STILL flashes to steam even with a dump zone and automatic damper unless an "experienced operator" is in attendance, than I would absolutely refuse to work with it under any circumstances. I suppose you cant use this while you sleep then, since you won't be in attendance? Are you experienced the first day you get it, or do they fly someone out to train you on it for the first few weeks until you qualify as "experienced"?

Now, if you want to do something like this in an UNpressurized system, you'd find me much less resistant. make a water jacket and pump out of it with a nonferrous high temperature pump of some kind, maybe with a tempering valve, to a heat exchanger. put in filtration to prevent heat exchanger clogs. Now I wouldn't care at all, it would just be a teapot and if power failed it would just harmlessly boil. no harm, no foul.

but doing it pressurized in the living space, short of in a well tested pressure vessel with multiple failsafes that doesn't require an "experienced" operator is, in my very humble and professional opinion, stupid.

the gas appliances, of course, are installed by licensed professionals with proper monitoring equipment and are serviced regularly to make sure they are still operating in acceptable tolerances. Not doing THAT is also stupid. When you have that kind of safeguard for these units, they are tested and listed, and they don't require the boiler guy to live in your house to run it safely, then I will sound a little less shrill in my condemnations. Before that, it's "cowboy" heat.

 
ME:
3. You'll need an open minded installer, or a very old one. These stoves are vented, meaning that they need an expansion tank and are more susceptible to corrosion. The U.S. HVAC industry switched to pressurized boilers long ago, and are accustomed to safety features, like automatic damping and quenchers, that aren't usually found on wood stoves. (My eco-boiler has automatic damping and rust control.)

YOU:
 Now, if you want to do something like this in an UNpressurized system, you'd find me much less resistant.

Umm, who said anything about pressurized, be it insert or integrated water jacket? My stove is a giant teapot that should boil harmlessly if loudly, as are 99 percent of the wood stove boilers made in Europe.  The schematic in my first post shows an expansion tank, for heaven's sake.

As for experience, the point of DIY -- and this website -- is that your average attentive fellow can puzzle it out if he does his homework.

Anyhoo, Gmink21, you now have an idea of the North American understanding of the role of wood in multifuel systems: prejudice unsullied by fact.  STSS is the exception. Sven, the owner, has been doing multifuel since the '70s and is an exceptionally helpful fellow.

To get back to your question, if your entire annual heat load is the equivalent of a cord of wood, you can rule out a bunch of stuff. Payback on geothermal could be in triple digits. A ducted fireplace, which is the other way to turn wood into central heat, likely would drive you outside on all but the bitterest nights. Dunno about the economics of solar hot water plus storage, but adding a wood boiler would cost ~ $3k plus install.
You need to break down your heating requirements to understand the problem. If your architect can't tell you averages and extremes through the heating season, you can guessitimate them using UCLA's HEED software. http://www.energy-design-tools.aud.ucla.edu/heed/
If you need supplemental heat at 5 am with the thermometer in single digits, for example a split mini won't be very helpful. You may not need AC at all. Heed also has screens that allow you to compare fuels and furnace types.  

If it's unpressurized, what's with all the worry about boiling then? Why not just engineer it TO boil like every teapot on every wood stove in the world? Just because there is an expansion tank doesn't mean it's unpressurized. Since your system has an "overheat discharge" which I think would be completely unnecessary in an unpressurized system that can boil harmlessly, and it would not require an "experienced operator" in that case as well, I assumed it was pressurized.

If it is though.. again, I apologize, sometimes I do have to do that a lot. In my defense, that is different than the inserts being sold out there that most people in the US are asking about... including the original poster on this very thread and several previous in this forum... which tie directly into pressurized heating systems. They are very bad ideas.

the point of DIY is myraid. but it is not to take dangerous risks unnecessarily, as most of the inserts and add ons out there do. Your particular product may be an exception. And when it's listed, sold without an indentured servant trained in its operation, and can operate without a dump zone, I would install it in my living room.

harmless to humans. not so good on the plumbing. I am perhaps being overcautious. Your caution is clearly excessive, unless you believe that American homeowners can't handle decisions their British counterparts several times a day this time of year.
If you followed gmink21's link, you'd find a fireplace insert that has more safety features and better performance than my stove.

So is the consensus that I should be looking into small scale nuclear reactors instead?? Just kidding...

I didn't realize it was such a big controversy. I am just a tad confused as well. I would think that there would be some type of option for people who wanted a fireplace but didn't want to waste the energy up the chimney. WHen I read about these at first I figured what a great idea. Apparently they are unsafe though? I don't understand how they would be. Rob could you explain a little more in laymens terms as to why I wouldn't want one of these in my home? I feel like you think that it is the equivalent of a bomb. If this is the case then I definately dont want one. I cant seem to grasp why these would be popular in Europe but not over here. AFter speaking with my architect we may avoid the fireplace altogether, due to the level of insulation and air sealing we are aiming for. My original thinking was this.

I want a tight, superinsulated home that doesn't use fossil fuels. I want a solar thermal system. I will need to have an emergency automatic backup to keep the house above freezing (mini split). I want a fireplace. I want a supplemental heat source that I can use when the days/nights get particularly cold. Why not use a wood stove insert back boiler than can look like a fireplace but help to heat up my hot water supply? My final thought was: Is this a bad idea? So i asked on here. I am still unsure if I need/want to do this.

Smarter about the '70s energy shock, Europe raised taxes on oil to make alternatives attractive. While the U.S. stove industry languished in cycles of boom and bust, its European counterpart flourished. This stove is a 93 percent efficient gasifying boiler built for German living rooms. http://www.he-energy.de/walltherm.htm
You won't find these stoves here because of (a) the aforementioned feast or famine (b) the U.S. prohibition against selling stoves not certified by the EPA and (c) people like NRT Rob who think it is still 1975 in Germany, too.
It's a shame because these stoves fit passive solar like a glove.
Gmink21, I wouldn't deprive yourself of cozy flames if you are so inclined. A garden variety masonry fireplace shouldn't overheat your house or chill it unduly if you fit it with an outside air supply and tight doors. http://masonryanswers.com/tech/design/fireplace1/efireplace/efireplace2/efireplace2.html You are still green on the basis of R value. Very green.

re: wood stuff:

I looked and I again see a dump zone required. That tells me the unit is not built to harmlessly dissipate heat at the stove. That tells me it is not truly safe for installation in a residential space or a heat dump would not be required. A proper unpressurized system would not have that requirement, like every water jacket on every wood stove for the last two hundred years doesn't have that requirement because it is open and unpressurized and just boils if it gets too hot. THAT could be pumped out and exchanged into a regular heating system safely. the only downside is you have to refill it with water periodically of course, if you don't, nothing bad happens except losing water heat. and you can solve that pretty easily. that's only on a wood stove, of course, though the idea could be used in a custom fireplace assembly as well.

I don't care what the Brits allow or do. In the case of these types of system, anything that is "not so good on the piping" is by definition dangerous to humans. It's not like half of europe is out there heating with wood in this manner, this is a niche product. the fact that there isn't a pile of burned bodies to point at doesn't exactly fill me with confidence.

A link worth reading: http://www.woodheat.org/dhw/dhw.htm proper safety precautions SHOULD prevent situations like this from occurring, but it seems to me mr. Todd here doesn't really understand what pressure can do in pipes. Passive heat dumps help, and that's good, but again I don't understand why it would be required if a truly safe system were designed. and ANYTHING that requires an "experienced operator" is an automatic fail: you are not the only person who is going to live in this house. If that appeared anywhere in a manufacturer's literature I would rule it out immediately. might as well replace the sentence with "this product is not ready for sale".

I haven't seen any systems yet that I would be willing to put in my house, and I burn wood every day in the winter, and have burned it most of my life. I'm not saying the systems will kill anyone who touches them. I am, however, saying that I don't consider them safe and I don't think they are particularly well engineered. that plus the insurance issues are why I would never consider them until something more like the "water jacket" deal is delivered and covered by your homeowner's policy.

Re: basic heating plan:

If your heat load is small enough as it sounds like it is, you could simply use an electric boiler backup, which would be just like doing geothermal but less efficient (you'd be looking at something like 6000 kwh/year for heating if your architect is right, minus your contributions from other sources). If your electricity isn't green enough though it wouldn't be green with geo either. There is a brand new unit out there that might fit you if heat pump tech is the goal, the Daikin Altherma. but when I say brand new, I mean it, pricing just hit the street up here yesterday. and I don't know what your water temp requirements are. And that assumes you're ok with using the juice which is likely generated by fossil fuels. if it worked you could divide those kwh by 3 or so if the MFG isn't totally full of poopy. there would be no economic payback in your case but it would reduce usage.

other than that though your options for non-fossil fuel are limited. you could do a real wood boiler which has the multiple redundancies built in to do this safely. If you built tubing into the fireplace itself and had enough mass that it's not possible to overheat the center that might be an option as well... you'd have to control it to avoid heating the mass when you were using another source though.

I think if you are not going to be using backup heat normally though I would use an electric boiler. cheap, effective, and for limited use it's not much worse than a heat pump either geo or air.

http://www.builditsolar.com/Projects/BioFuel/DougMasonryStove.htm masonary stove that heats water as well. Tempcast masonary heaters have lots of customers that have installed wwater heating coils as well. http://www.tempcast.com/testimonials.html

http://www.heatkit.com/html/projects.htm#hot water Worth looking at this page as well.

From the website recommended by NRT Rob: "The first thing that needs to be said is that a wood stove is not the right device for heating water for in-floor radiant. You would never get enough heat off a wood stove to make a dent in radiant heating needs."

Holy smoke! Did someone forget to tell the Europeans?

Keep reading NRT Rob. You might be up to 1983 by now.
i

I'm sorry, I'm too busy training to safely operate my heating appliance to stay up to speed on these "cutting edge" developments.

That quote is definitely off track. It does not make the operator of the first stove in the list un-explode it, however, that the wood heat guys are not hydronic heating experts. it is an example of why you cannot depend on an experienced operator to be a safety feature. Because people move. houses don't.

I think my requirements are quite simple: the unit should not require training or much experience to operate SAFELY if the homeowner is going to be involved... though efficiently, well can be compromised until the operator gets up to speed. That's it. ideally, it wouldn't need a heat dump either since there is no need for it in a true unpressurized situation. I'm suspicious if one is designed in "just because". if you want a full fledged, fully redundant automatic dampened dual relief valved passive heat dumped wood burning appliance in your living room, great, but at that point you're not saving much and a real wood boiler would do the job better and more safely with the dangerous equipment not sitting there two feet from you in your living room, with a proper storage mass of some sort designed in as well.

That explosion resulted from an install fault. No mechanic on either side of the Atlantic would have put valves in a thermosiphon loop. (Hurdle 6: A leak in a properly designed wood stove boiler will keep leaking until you turn the makeup water off, which in the case of my stove is a 3/4 inch supply.)

Let's agree that these stoves aren't for everyone, here or there. Myself, I consider myself as smart as your average renewable minded European homeowner. Now all I need is a stove mechanic who is as smart as his colleagues on the other side of the Atlantic, or at least try to won't cover his ignorance with a patter of BS.

ouch

hows that insurance policy going to read.....Denied, non compliant product for US market.

Dan

I think I would vastly rather leave it at: most of the inserts being hawked out there are potential bombs, tying directly into heating systems that operate under pressure.

the ones that aren't still seem awful concerned with automatic heat dumps. that's puzzling, bit of a mixed message there. Feel free to continue the class if you can explain why.

Your unit is a boiler with a pretty view window. That's very different than most of the firebox units out for sale in the US. Even so it still has that puzzling mixed message, one that doesn't exist with most of the unpressurized wood boilers we have here in the US. One has to wonder why.

but hey, if by "not for everyone" you mean "not for anyone who ever wants to sell their house, and not for anyone who cares about any future occupant of the house having to sell it", I guess you're right. They are "not for everyone". "Smart", or not.

"the ones that aren't (potential bombs) still seem awful concerned with automatic heat dumps. that's puzzling, bit of a mixed message there. Feel free to continue the class if you can explain why."
(Agitprop 101: play dumb and see who steps in it.)
Wood stove boilers can't be readily extinguished like oil or gas boilers, so they need to be designed to shed heat in any situation, including a power outage. There are probably thousands of stoves in Europe idling uneventfully in emergency mode at this exact moment, but NRT Rob won't countenance actual history, setting forth instead his "requirements." Like GM saying I don't care how Toyota does it.  But judge for yourself. Read the pdf I linked in my first post, which lays out the issue in very plain English.

but hey, if by "not for everyone" you mean "not for anyone who ever wants to sell their house, and not for anyone who cares about any future occupant of the house having to sell it", I guess you're right.

I have $2,300 in this stove, which should work out to about $115 a year for my time in the house. I hope to tell the buyer that passive solar works so well I didn't need it. (One of the tough decisions in passive solar is how much to pay for backup heat you hope never to use.) Even if I can't, it will pay for itself many times over because the abundance of firewood here means $0 as an annual fuel budget. When the time comes I'll look the buyer in the eye and decide.

hows that insurance policy going to read?

Dunno, but I am building with cash so the only 'aye' that counts is mine.

I think I would vastly rather leave it at: most of the inserts being hawked out there are potential bombs, tying directly into heating systems that operate under pressure.

(Agitprop 101: when your answers reflect embarrassingly basic misunderstandings, like vented vs pressurized, reframe the question.)
But, OK, in the interest of moving on, rotten insert scoundrels!