Wood Doctor Boiler (converter)

There's a Wood Doctor dealer a few miles up the road from me, Fredman. The other day I noticed a weird-looking new unit sitting with all the stock Docs. My guess is that's it. I'll check it out next time I get by there and file a report.

I've got a Wood Doctor dealer near me also. A couple years ago he removed a big Central Boiler and installed the new style Wood Doctor for his own home/shop. They've been out long enough to have some "real world" operating results available.

ive seen wood doctor on the net and have no dealers in my area but they have had the converter out for a couple of years now. id like to see one in person and see how they work.

I have a dealer near me as well. I called several times and finally got to talk to the guy and he said I didn't want the converter, way too expensive. Talked me right out of it.

Eric

My husband and I almost bought a Wood Doctor outdoor wood boiler and then when we started asking around, we decided not to purchase one (it was used; only 2 years old and like new and we could have gotten it for half the price of a new one). We were very excited at first because we thought that we had come across this fantastic deal and then we started asking ppl about them and found out that they require a lot of maintenance (not regular maintenance, but often need the box welded...this is a huge problem with them)...we called plumbers and every single one of them said that the Wood Doctor's are major headaches for the ppl who own them...we spoke to 6 different plumbers who ALL said the same thing. At first we didn't want to believe one or two impressions but after a full concensus of plumbers and speaking to current owners (2), we decided that they were more of a headache than we would like! I'm sure that not everyone has had major problems, but it seems that most WD owners do...hope this helps...

I too am interested in the Converter. It says on their website they're good for up to 7,000 sq ft. All I'm interested in is an OWB that doesn't drink down wood.... looks to be a down draft gasifier. Similar arrangement to a Tarm, although the water jacket in the WD looks to be pretty extensive from their crude cutaway.



http://www.wooddoctorfurnace.com/converter.html

That's interesting. I wonder why it sucks the air out of the stack instead of blowing it into the firebox. That's a pretty elaborate air-to-water heat exchanger. I wonder how you keep it clean. It's also a lot of potential weld failure points, at least from what the diagram suggests.

I would like to see refractory in the firebox to hold heat and protect steel....That is the knock I've heard on this unit...lack of sufficient firebrick....and the price of course....

Eric Johnson said:

That's interesting. I wonder why it sucks the air out of the stack instead of blowing it into the firebox. That's a pretty elaborate air-to-water heat exchanger. I wonder how you keep it clean. It's also a lot of potential weld failure points, at least from what the diagram suggests.

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After looking at a bunch of the European boilers, I noticed that the Kaukora Econature and the Viessmann Vitolig 200 both have induced draft near the stack rather than forced draft just before the firebox so it must be a fairly common setup, and maybe an efficient one. It seems everywhere you look now someone is coming up with a new design and calling it a gasifier so I'm sure that other people's designs get parasitically copied into some 'new and improved model' of another company's previous design.

the Garn is basically a induced draft pulling the air from the door into the fire chamber or they call it the nozzle and out the long exhaust tubes. the herlt boiler from Germany has a similar design with induced draft.

I think the new Euro's are pulling (rather than pushing) through the door because it allows them to have servomotor driven shutters for both primary and secondary air. You would otherwise have to use variable speed fans which, though certainly do-able, is more difficult to set up and control. The purpose seems to be closed loop control to an oxygen sensor for ultra clean burn at low firing rates.

That's interesting. Pretty rough operating environment for that blower, I would think.

Actually, the only boiler I've ever seen that on is a Wood Doctor. I'm not aware of any European-style gasifiers that pull exhaust out the chimney.

The Viessman Vitolig 200 has it- just looking last night actually (www.viessman.de). As does KOB, ETA, Herlt, etc. The blower is in the exhaust stream driven by a sealed shaft from a motor which is mounted wholly outside of the boiler. As long as the seals are good, it will remain robust.

Of course the environment, though hot, is likely not as bad as you might think given that flue gas temps are under very close control via the oxygen sensor and temperature feedback to control of both air inlets. I wonder if they see nearly the flue temp rise on startup that you EKO and Tarm guys are noting.

EDIT: Just reread your post, Eric. The blower is pulling through the boiler (where the EKO pushes), but still pushing up the chimney. The point of pressure change is still within the boiler itself, just at the start of the smoke pipe rather than the door.

I was wondering where the different boilers had the blowers. I'm actually surprised someone would want the blower pushing into the firebox. Seems like a great way to make a big mess. Like when you open the door and forget to shut the blower off first. With the blower after the firebox you could open the door while the blower is running. The motor wouldn't be in the hot gasses but the blades of the fan still would be which might be trouble.

Blowing air into the firebox is the main reason I'm holding back on the idea of buying an EKO.

Induced draft is the name of the game here. The Garn uses induced draft to pull combustion gases out of the chamber then they are replaced/mixed with fresh air. One problem I see with trying to control to different airstreams with one blower on the suction side is that the only way to control flow is with baffles. Somebody on this thread mentioned the the fancy European gasifiers use servos to control in sync with optimum combustion on downdraft models. I think this would be the ultimate setup.

Big benefit of ID is that there is a vacuum in the chambers so smoke is pulled away through the exhaust. Works real well when cleaning ashes. The way I understand the primary/secondary mixture or tuning is like setting a cutting torch to achieve optimum flame for cutting- nice and blue. You are adjusting two different gases at two different pressures to achieve perfect mix.

So do you think that a blue flame is optimum for gasifiers, or are you just talking about gas welding? I usually get orange or bright yellow, but the other night after loading the stove up for the night, I was getting a blue flame. My guess is that wouldn't be the best time to observe optimum burn, however, and all the promotional literature and videos show yellow or orange flame.

I was always told that a blue flame is a neutral flame. It is not O2 starved. My boiler can emit a blue flame into the secondary chamber but it is sometimes hard to see into the back of the chamber.

EricV said:

I have a dealer near me as well. I called several times and finally got to talk to the guy and he said I didn't want the converter, way too expensive. Talked me right out of it.

Eric

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Thats funny stuff there!

Well I decided to buy one while their promotional sale was on this past July/07.

Out of the box, its not for someone that just wants to add wood and forget it, some shortcomings have to be fixed.
- All doors and their hinges are equipped with grade 0 bolts or less and the nuts grap the door hinge and so on...
- controls are two aquastats, hi-limit and controler, and has no idea when its out of wood, hence will run stack blower forever until
someone turns off main power, very primitive for $8,500 plus cools your 1,000 litres inside the unit.
- Does not reach the advertised 2,000 degrees due to a couple of factors, the unit is not combusting fully or reaching clean burning, but system is all of
1,000 litres (1000/3.78=265 us gal). My main indicator is as I have to sweep my exchangers frequently as the buildup acts as a thermal barrier.
Plus the house uses about 85k btu/hr at -9C or 15 degrees outside and unit runs at about 148k btu/hr hence lots of cycling - not good.

Must say it wants to be loaded and worked, and our second building did not get connected to the loop, which would have solved some of
the incomplete combustion problem - no secondary air IS the main problem!
It takes 4 - 6 minutes aprox. to achieve almost smokeless operation

Fixes needed:
Doors and hinges are not going to last period
More CFM so a system of secondary air could be installed and not take away from the cfm going through the firebox and down to final combuster.
Creasote runs down over the inside bottom of the loading door causing air leaks
Primary air should be preheated some what
Controler could use a greater delta T in its operation of when to start firing (as is now 158 - 178)
Firebox is too wide at the bottom or not enough taper, leaving some charcoal behind but more blower it might be perfect.
Loss of 36 gallons(US) a month via evaporation - too much!
Too many doors more complicated than necessary.

It is really easy on wood for such a big unit(4 x 8 foot print) and it likes small wood no larger than 4" round(small is better lol)
It also prefers about 1/2 to 2/3 of a load over a full load??? maybe due to the short firing cycles.
With water storage that is matched to its firebox capacity ie. one load heats the entire water capacity,
it would be an amazing boiler, but other manufactures have more refinements for the same price.

Bottom line, I like it but the junkie doors and no secondary air, I would not buy it again, HERLT or Garn only
are the two so far.

PS the Sequoyah E3400 is very similar to the wooddoctor converter, but CAN NOT Clean the EXCHANGERS if
something goes bad, improperly sized, or cycles are to short etc... your screwed! (the world is not the manufacture's lab.)

NICE SITE!

thx
doug

Welcome to the Boiler Room, Doug. Very nice analysis and I'm sure, food for thought and further discussion. I hope you'll stick around and contribute to the discourse around here.

Eric Johnson said:

That's interesting. Pretty rough operating environment for that blower, I would think.

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It is the best place for the fan, from a standpoint of achieving and controlling combustion. Essentially mimicking a chimney draft.

But, as you noted, it's a rough operating environment. So, the debate is between the best place for control of the fire, versus the best place for reliability (and, resultingly, cost - making flue fan reliable costs a lot).

I don't think there's a "right" answer to that one, because it really is a balancing act. Either works, and either has advantages and disadvantages.

Joe

Actually I use a Sequoyah E3400 and besides the fact that the heat transfer areas are self cleaning and I have never had to clean them, it is very accessable through a cleanout door on the back that was installed for exactly the reasons that were stated.

WD convertor update

After doing a little video of the secondary combustion passage, noticed a cracked vertical brick(that makes up the slots leaving the firebox).
Closer look, all of them are toast! Replacement SBI bricks end up taller by 3", forcing to add an entire new level of brick to the firebox.
SBI brick i put in, on the UPC label states fired up-to 2000 degrees F, should be no worries now. 1 brick $5.49 each!! and are feather light.

Wooddoctor really needs to update this converter or shelf the thing and in the process save people's hard earned money and Time on repairs doing what should have been
done at the factory!

With the new brick(Much better) I will report on if it will crank more BTU's/hr. presently ≈ 161kBTU/hr and my wood is outside temp as it enters the unit(frozen).

After all the mods it will be a good unit, next project is to dial in the correct air/fuel ratio as the blower is only 110 cfm on a good day

I'm seriously considering a programmable temp controler with J or K type probes and the controler will control a variable speed blower motor. Giving me control with air flow
based on my desired temp setting. Out of the box it screams for more air.
Any thoughts are most welcome.

thx

Fredman said:

Garn or EKO is what I am going to get when the time is right.

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A little bit of advise is to see ALL of the manufactures then narrow it.

Hence you may want to look at a Herlt - probably the very best gasification boiler made, definately their controls are on anther level.

Are they available in USA?? they are sold out of Calgary, Alberta.

thx