I’m a new member to this forum and I like to gather some input on a very specific topic.

I’m involved in the design and manufacturing of indoor wood boilers with visible fire.

In recent months we were contacted by several professionals involved in the construction/design of passive houses, with the question if we could build/design an indoor wood boiler with visible fire (water stove) with an overall heat output of around 15,000 BTU/hour. Part of this heat would be radiated into the room where the unit is installed, the balance would go to the water and used for heating other spaces or domestic hot water preparation.

We did some research into this topic and came up with the following concept: the "ideal" indoor wood boiler, construction wise and towards particul emissions, would have an overall heating output of around 30,000 BTU/hour of which around 20,000 BTU/hour will go to the water and 10,000 BTU/hour will be radiated into the room. The unit would have a single pane viewing glass. The 10,000 BTU/hour of radiant heat can furthermore be limited by the use of a double or triple pane viewing glass, and consequently more heat would go to the water.

This 30,000 BTU/hour wood boiler would also require the implementation of a small buffer tank (50 to 100 gallons), to store the heat for later use. This buffer tank can also be used in conjunction with a solar hot water collector system mainly during the spring and summer months when the wood boiler is not used.

Question: Does this size (30,000 BTU/hour) indoor wood boiler with visible fire seams right for the passive houses currently under construction/designed?
 
For more information on the concept of these indoor wood boiler you can visit the website below.

Thanks for your input.

Marc

Hydro-to-Heat-Convertor

My friend Peg had an old kitchen cook stove hooked up to a tall narrow copper water tank 35 years ago. It about time someone updated the woodstove water tank! I have a client that wants a woodstove in their small energy efficent house - maybe this is the unit?

http://cgi.ebay.co.uk/Stratford-SEB-20-Multifuel-Woodburning-Boiler-Stove-/110416243419?pt=UK_HG_FireplacesMantelpieces_RL&hash=item19b5522adb

Figure $3,000, including freight. No import duty. I used Pilot Air Freight.

If you want to drag the US stove industry into the 21st century, Marc, do the EPA testing on a line of modern European stoves and start importing.

What are the rocket stoves all about? Are they good candidates for interior heating?

Posted By Fire&Water on 09 Dec 2010 07:46 PM
I’m a new member to this forum and I like to gather some input on a very specific topic.

I’m involved in the design and manufacturing of indoor wood boilers with visible fire.

In recent months we were contacted by several professionals involved in the construction/design of passive houses, with the question if we could build/design an indoor wood boiler with visible fire (water stove) with an overall heat output of around 15,000 BTU/hour. Part of this heat would be radiated into the room where the unit is installed, the balance would go to the water and used for heating other spaces or domestic hot water preparation.

We did some research into this topic and came up with the following concept: the "ideal" indoor wood boiler, construction wise and towards particul emissions, would have an overall heating output of around 30,000 BTU/hour of which around 20,000 BTU/hour will go to the water and 10,000 BTU/hour will be radiated into the room. The unit would have a single pane viewing glass. The 10,000 BTU/hour of radiant heat can furthermore be limited by the use of a double or triple pane viewing glass, and consequently more heat would go to the water.

This 30,000 BTU/hour wood boiler would also require the implementation of a small buffer tank (50 to 100 gallons), to store the heat for later use. This buffer tank can also be used in conjunction with a solar hot water collector system mainly during the spring and summer months when the wood boiler is not used.

Question: Does this size (30,000 BTU/hour) indoor wood boiler with visible fire seams right for the passive houses currently under construction/designed?
 
For more information on the concept of these indoor wood boiler you can visit the website below.

Thanks for your input.

Marc

Hydro-to-Heat-Convertor

what is the general requirement by homeowner for upkeep and how often do you need to refill the firebox?   Just curious how that works if you are gone for a weekend or working all day for temperature maintenance etc....

Europe has indeed a lot of manufacturers of these indoor wood boilers. Unfortunately none of them meets the US EPA requirements. There are also several issues with UL requirements.
The unit from Stratford is a design that is around 20 years old and more important it has underfire primary air combustion what realy is a killer to meet US EPA requirements. To meet current US EPA requirement these units need to be desinged for it, meaning staged combustion with some sort of afterburn system before the the flue gasses hit the heat exchanger to extract the heat out of these gasses.

For what concerns the upkeep, these units are typically used during evenings. Load the unit around 5PM-6PM and let it burn for 6-8 hours. When the fire dies overnight the main system kicks in when there is demand for heat.

I was more looking for input on the BTU requirement for an indoor wood boiler like this for use in Passive Houses.

OK here goes, I have a small house, 2000 ft^2 inside the thermal envelope.
It is moderately insulated and well sealed but not passive house by any means.

I run a Waterford Leprechaun stove as my primary heating. The firebox is about10X12X16” and the stove is good for around 22,000 btu full blast. In the middle of the winter I start it around 5:30 in the evening when I get home. I get it good and hot and then close the damper all the way run it until I go to bed around 10. Typically it takes about 3 loadings per evening. Once the house is heated up to around 65- (about an hour). I close the damper all the way. By morning the house is low 60’s. If it is sunny the house is still in the low to mid 60’s in the afternoon. If it is not sunny the temp is59-60 when I get home.

The house has a lot of thermal mass. If I run the woodstove on low for 12-15 hours or so and start with all the thermal mass is warmed to ~70 degrees, the house will typically loose 6-10 degrees every day in the winter. Shoulder seasons I run the wood stove every other day, unless it is sunny. I have to do short burns and partial fills not to cook me out of the house. So I figure a boiler that could generate ~ 100-150,000 btu’s in an evening and a way to store the heat would be about perfect. If you were going with a 30 degree delta of usable heat rise in water, a 500 gallon tank would be ok and have about120,000 btu’s of storage. Maybe decrease this a bit for a true passive house.

Cheers,
Eric

Marc, you perhaps don't remember that we talked several years ago about the belgian stoves you were selling on eBay. http://web.archive.org/web/20060212032228/hydro-to-heat-convertor.com/aboutus.html
My question then was why I couldn't find your models on the EPA's list of approved stoves. Still can't, searching by your various names plus Burlington MA. Apparently there is no requirement for wood stove boilers, indoors or out. Correct me if I am wrong.

I am happy to see you participating in the voluntary EPA programs for hydronics and catalytics. I am also happy to see that you are making the stoves here now. Mitigates the NIH factor.

Or does it? This study disagrees with your assessment of European technology: http://www.mass.gov/Eoeea/docs/doer/renewables/biomass/DOER%20Biomass%20Emissions%20&%20Safety%20Regulations.pdf It describes EU boilers as having "far better emissions performance" than U.S. counterparts, largely because EU standards "are almost an order of magnitude tougher" than the strictest US std (Massachusetts.) The reports says EU manufacturers would expect no problem meeting the EPA's hydronic phase 2 requirements if they had a reason to do so. In fact, if air quality bureaucrats could be wistful about stoves not sold here, you'd read it here.

As for my stove, Stratford's Eco-Boiler design is about three years old. Its design innovation is a crossflow integral water jacket that extracts 70 percent of the stove's heat as hydronic. I see that your best performing stove does 60 percent. The Eco-boiler is 72.2 percent efficient. EU compliant. 757 degree flue gas temp (the key to clean burning.) www.eco-boiler.com.

Hi Toddm, sorry I don't remember our conversation, but your are correct, in 2005 I was importing indoor wood boilers from Belgium. They were tested at OMNI and ... EPA exempt ... at that time, and still today they would be in the grey zone of EPA certification yes or no.

Since 2008 we develloped our in house combustion concept that makes it possbile to meet US EPA requirements for partical emmisions today but also in the near future when emmsions standards will become more stringend.

In August of this year our model B100 was tested at Intertek. Emmsion results were excellent but the unit could not be certified to the EPA Hydronic Heater program because it could not be opereated at a Cat II burn rate. So, it is clear that the US EPA hydronic Heater program "regulations" or test protocol is put togetter to clean up the real outdoor woodboilers issue. This is also the reason why for instance you don't find Tarm boilers or Froling boilers on the list. They all burn very clean but they all can not be operated at a Cat II burn rate or lower. A CatII burn rate is a burn rate at 25% of the max burn rate. The European standards have a 30% cut off burn rate at the low end.

Our current models are made here in Massachusetts (Burlington/Billerica MA). Feel free to stop by if you are local.

Without reading all of the study you are refering to, I quicky looked over it, and it looks like most of the residential untis are gasification wood boilers with forced draft. Our concept has a natural draft, staged combustion with catalytic afterburn.
Not directly an apples to apples comparison.

For what cocerns your stove, the Straford, I do agree that a higer temperature is better, but this is to be understood as combustion temperatures, not stack temperature.
A stack temperature of 757 degree is basically wasting most of your energy up the stack.
Look at some of the gasification boiler, and also our models, they all have stack temperature at high burn, of around 350F and 220F at low burn. This low temperature is because of the heat exchanger design that extract most of the heat out of the flue gasses and gives you the high overall efficiency. Keep in mind that combustion efficiency and overall efficiency are not the same.
Just a simple calculation, assume you firebox temperature is around 1500F, and believe me it will be not much hotter if at all it is, then with a 750F stack temperature you are roughtly at 50% overall efficiency.
So, lets put it this way, we can NOT compare (apples to apples) the European standards to the US standards.

The European standards are focused on CO2/CO and to a lesser degree on partical emmsions. The US EPA is focused on partical emmsions.
Low partical emmisions means low ppm CO, but low ppm's on CO does not mean low partical emmisions.
And this is the basic reason why, besides the European gasification woodboilers, you don't find any European wood boilers on the American market, let alone that they would be able to pass US EPA standards.

Do you have any input on the BTU requirments of a passive house?

"Without reading all of the study you are refering to, I quicky looked over it, and it looks like most of the residential untis are gasification wood boilers with forced draft. Our concept has a natural draft, staged combustion with catalytic afterburn. Not directly an apples to apples comparison."

You are right, of course. The European stoves are superior technology.

"So, lets put it this way, we can NOT compare (apples to apples) the European standards to the US standards."

So if the tests are an impediment, fix the tests. Or as the study concludes, "Europe has demonstrated that clean burning devices can be produced. The question is how more efficient devices can be moved into the U.S. marketplace."

I repeat, start importing European indoor boilers and stop hiding behind phantom EPA "regulations." http://www.epa.gov/burnwise/pdfs/FAQs10-22-08VT.pdf "EPA’s Phase 2 Voluntary Partnership
Program: Hydronic Heaters" BTW, I don't find you on EPA's list of Phase 2 "White Tag" stoves either.

I am no expert on PassiveHaus design, but I suspect that 30k btu/hr is oversized without substantial storage. I know for a fact that a buffer tank of 50 gallons to 100 gallons is not substantial storage. European retailers will tell you to err on the side of undersizing indoor boilers. At your rated output, 100 gallons of room temperature water would be boiling inside three hours. At my stove's rated output of 40k btu/hr, my 300 gallons of storage plus 50000 pounds of hydronic slab wouldn't reach critical points until I refueled it twice. As you know, a hot burn is an efficient, clean one -- a strong argument against using EPA's high- and low-output tests, designed for outdoor boilers, on stoves meant to be used in an entirely different manner.

Hi Toddm, not that I disagree with all of your arguments, we do have some common ground.

I also "tried" importing European models: Belgium, UK, Italy, Germany, ... .

There are some fundamental issues:
- I do have wekders / fabricators employed and I don't want to lay them off just because. I'm a strong believer in manufacturing "stuff" right here.
- When you are importing you are not in control. You can be without a product within a couple of months if business relation goes south.
- To import you need voulume, and volume is not there and will not be there for the next 5 years in my opinion. So this gives my company time to build this.
- Also the Euro exchange rate is way to high. For instance Wodtke Mono, what is a unit that can be certified to EPA requirements, sells for $4,500 to 5,000 Euro in Germany, that is $5,850 to $6,500 without import related costs. This is roughly 25/30% more then a similar unit in our line of wood boilers. Forget offering products at $3,000 if you import. We need to manufactur them in the US to get the price down.

I share your opinion on storage, but also here cost will be an issue.

Where are you located?

I commend you for slogging on. I think we can agree that the disregard for indoor boilers on this side of the Atlantic, in favor of the outdoor kind, pollutes the air, wastes wood and poisons the climate for what is, in my part of the world in so central Pa, an abundant source of renewable energy.

It is doubly frustrating to see a mass market and commodity pricing in Europe and hear disinformation here about the capability and safety of these stoves.

It can be done on a budget, which was my initial point. My system should cost $6,000 to $7,000 all in, depending on the hydronic slab finish out. And legally, in my local jurisdiction anyway. The EPA's hydronic program doesn't apply twice in my case, first because it's voluntary and second because it's tailored for OWBs and a style of use I consider a crime against nature.

I know I'm a bit late on the draw on this one! But, I've been looking for the same and there is no product available like this in North America that I can find...

I would like to install the eco-boiler in the small (750sq ft up, 750sq ft down) passive solar home I'm designing, as its on 10 acres of land in wood lot country! Definitely want to go infloor hydronic radiant heat, as I plan to go with a stained concrete floor anyway for thermal mass.

Get in touch Todd, I'd be interested in hearing how you've made out with that setup! Kudos to you for thinking outside the box,

Kenny

Sorry for the delay. I have been full time construction since labor day. http://www.flickr.com/photos/58061641@N06/
The pix aren't up to date. I am roughed in and dried in and wrestling now with how to put electric in walls of solid AAC block. I think I have a way to make surface raceways look presentable. There is no reason my house should be conventional in any respect. Ha.

No stove yet. I have to weld up a surround that will make it look like I set it in a fireplace. The surround will move most of the radiant heat upstairs at the same time hydronic is heating the slab. I may be heating dhw this year. But the winter of 2011-12 will be the shakedown.

To answer the questions in your PM, Kenny, you'll have to run the numbers, based on your house design and climate, to see if an Ecoboiler is sufficient. It is important to recognize that these stoves are considered auxiliary heat even in Europe. For safety purposes, an indoor boiler should be undersized. For convenience, it shouldn't be used to the point that you wish you were stoking an OWB once a day instead.

The heat storage math for your slab is cubic feet times 150 pounds time 0.2 (the specific heat of concrete vs. water at 1.0) times change in temperature. The experts say you shouldn't heat the slab past 85 degrees because of comfort and expansion issues, so I am looking at 100k btu to add 10 degrees to mine -- after meeting contemporaneous heat loss. Figure the Ecoboiler will put 25k btu/hr into water for six hours burning dry hardwood flat out. I am also heating water storage for DHW and on-demand radiant heat upstairs. I might reload it once on a gray cold winter evening. But if it uses more than 2 or 3 cords a winter, there is a heat pump in my future.

I am happy to report that the highest point of my roof pokes out of the canopy enough to make solar hot water practical. I'll undersize solar (and heat pump) as well, and add a second storage tank if necessary. The goal is to have choices in a high-mass house that needs tweaks rather than blasts. The pros here consider my approach to be too organic, although multifuel doesn't seem to faze Europeans. But, hey, it might be. So far the wife sticks up her hand in mid explanation and tells me, 'you keel over, I'm selling.'

Nice photos. Nice project.

http://www.hhcelcon.co.uk/home This might help, it has been 30 years since I used AAC and I can not get it where I am or I would be using it for my current project. But from memory it was easy to rout for cables and boxes.

Viesmann are bringing in their smaller boilers, there are others breaking into the US market. Have a look at hearth.com.

But I would query radiant in floor a passivhaus sounds overkill for a very limited load.

I think I would go with solar and electric back up and a small stove for top up heating. 1500 ft at less than 10 btu sq ft. 3 or 4KW of electric has to be the cheapest bearing in mind realistically you are never going to use it but it keeps the powers that be happy. Your real need is for DHW and Solar can get your storage to very high temperatures and provide heat to a couple of small radiators.

ok, this may be a dumb question but with the discussion of importing, EPA ratings, etc., does that mean that if I'm in the US & I want an indoor gasification boiler, I can't get one?

http://www.hearth.com/econtent/index.php/forums/viewthread/72728/#846937

Look and weep.

5,000 Euros, so sort of same in Dollars, I am assuming tax and shipping would be a wash.

What you can and can nor do where you are depends on local regs.

I don't know how things have changed, but about 20years ago my brother bought a house in northern Minnesota with an interior wood burning boiler. He had a VERY hard time getting a mortgage and fire insurance. It had much more to do with UL than EPA.

Bruce

The answer is in insulation, windows and storage. Radiant floors are the lowest temperature emitter available and the slab is essentially free. Domestic hot water being the peak load a combination storage DHW/solar/propane or electric water heater is the answer.

With the proper design, including heat loads and controls a low temperature system is possible.

As for indoor wood boilers, it is a filthy business and only made tolerable if the boiler room opens to the exterior and air-tight to the living space.

The reason for the insurance issue is the general lack of knowledge about the proper installation, maintenance and operation of wood burning appliances in general and boilers more specifically.

I would disagree with in floor radiant , far too slow to respond. You have a very well insulated building, optomised for solar gain, sun comes up and there is your energy but you can not quickly turn radiant floor down. Or up.

Wood, well how much would you use? Half a cord a year, not much wood not much mess.

If you want to use wood but cleaner then pellets, a bag is 300,000 btus's and would last a very long time in this situation.

Can not find it now, but on an Austrian Manufacturers site I came across a stove for Passiv Haus, so small it looked like it burnt tooth picks.

I am not aware of any problems with wood boilers, a badly installed gas or propane boiler would worry me more, wood does not explode.