Help choosing between efficient wood boiler and wood gasification

What brand is the tc-500?

I would stongly encourage you to look into more than 130 gallons of storage. I had a Tarm with no storage and had trouble maintaining clean burns. I would fill the firebox all the time and have smouldering messes, especially in periods of low heat demand, like fall and spring. In a small house you are compounding the problem because you will need many small fires timed to closely meet your heat demand. If you don't light many small fires, you will end up with smoke and creosote. Add the pain in the butt factor of frequent boiler tending and you have just deceased the Wife Acceptance Factor to almost zero. A storage tank fitted somewhere in your small basement would enable you to fire and forget your boiler and pull heat out as needed.

Does Thermal Control have a website?

I almost went with a TC500 before I read about the Tarms (and like units). The Tarm I bought cost almost $7000, the 500 if I remember correctly was about $2100, so there is a HUGE difference in price. Had oil prices been lower, I may have went with a TC500, figuring it would have taken too long to pay for a Tarm at $2/gallon oil...but as the price of oil has shot up, almost anything you buy will pay for itself in a very short time period, so I thought about the long-term implication of wood handling and wood processing, and that tipped the scales toward gasification for me. I figured, conservatively that the Tarm will use 1/2 the wood; maybe less, and over the next 20 years that is what tipped me in favor of the Tarm. Payback for my unit is estimated to be 18 months or less at $4 oil..so the initial cost was not really a concern.

I think the TC500 looks like a real solid, low-end unit. I know folks who are very happy with them, and they last a long time and you can still get parts for the older ones. If money is a real concern, I would think you would be happy with the minimal investment one of these units require. On the other hand, if you can make the investment in a high-end unit, and think about the implication of having less wood to handle, less smoke, less creosote etc, you could probably be very happy with a gasification boiler too - once you get over the sticker shock.

..."if the system can burn longer and slower "...

Trying to burn long and slow with a water-jacketed wood fire is an almost unavoidable recipe for really poor efficiency at using the heat value in the wood, and lots of creosote buildup in the boiler and chimney. 15 years ago I rented a house with one of the really, really early non-gasifier Tarms and it was an unmitigated creosote disaster when I tried to use it in anything other than serious cold weather. Most places have only a modest amount of really cold weather, and you burn a lot of the oil in the in-between seasons, so a wood unit that only works well in the coldest weather won't really take you out of the oil dependency. For a long time that old Tarm had me convinced that wood and water should never be mixed in heating systems, until I witnessed a gasifier first-hand and heard how happy people are with them.

If you have a small space and don't want to get into the complexities and costs of a gasifier and storage, what about an efficient high-thermal mass woodstove like one of the soapstone Hearthstones? Leave your existing oil system in place (maybe use a power vent if you have only one chimney flue) and just set up the woodstove?

I agree with pybyr comments. The 130 gal water jacket is peanuts insofar as allowing efficient (no smoke, creosote) wood burns. Oil and gas boilers can use small water volumes because they burn full out, on and off, for short periods. You also want to burn full out with wood, but you can't have short on-off cycles and full out burn with wood. That's why the larger water storage to take the heat from a ful out, complete wood burn.

We heat 1500 sq ft house with a free-standing, wood stove in the living room. I also heat my shop with a Tarm and a 1000 gal LP storage tank. I don't run the Tarm at all during the off-season.

my father inlaw is running the small seton boiler with no storage and his burn times are 11 to 12 hours on dry pine with a 1500 square foot house. i dont know if that type of boiler wood work for you.

Let me take a stab at this:

ALL wood boilers, gasification or not, burn more cleanly and efficiently at full throttle. Prolonged idling is a bad thing and will cause the creosote issues described above.

There are three ways to avoid or reduce this problem:

1) Use a boiler that's small enough so that it can burn flat out more of the time.

2) Build lots of smaller fires, and let the boiler go out when heat isn't needed.

3) Use storage so the boiler can burn flat out for longer. Let the boiler go out between fires.

Using strategies 1 and 2, I ran my gasifier without storage for a year and had satisfactory results. Gasifiers do not require storage. IMHO, the claims of vastly improved gasifier efficiency with storage are a bit overblown.

However, an idling gasifier is not a gasifier. It has no better efficiency when idling than any other boiler. Non-gasifiers aren't typically very efficient anyway, so the loss of efficiency at idle is nowhere near as dramatic as it is with a gasifier. This creates the misconception that gasifiers require storage. Let me use an example:

My brother had a conventional boiler. He took pains to run it as cleanly as possible. Always at full throttle with dry wood until there were only ashes left -never idled at all. His combustion efficiency was around 50 to 55%. I'll use that as the peak efficiency for a conventional boiler. I don't know the efficiency of an idling boiler, but lets assume that it's around 35%.

He replaced the conventional boiler with a gasifier, which has a combustion efficiency of about 90% (actually more in his case - it's a condensing gasifier).

Idling with his conventional boiler would reduce his efficiency from 55% to 35%. You'd notice it, but it's not dramatic.

Idling with the gasifier would reduce his efficiency from 90% to 35%. That's a huge loss. The gasifier isn't worse than the conventional boiler, it just has more to lose.

If you want clean burn and efficiency, you need to build fires when you need heat and let them go out when you don't. This is true whether the boiler is a gasifier or not.

Storage can dramatically increase the time between fires and improve your comfort by reducing temperature swings in the house. If you want to keep the fire going all season, you don't need storage, but you will have increased wood consumption and creosote. In that case, be careful to buy the smallest possible unit so that it can run hot more of the time.

My brother saw a 40% reduction in wood consumption going from an optimally operated conventional boiler to a gasifier. In a situation where the boiler idles a lot, the reduction would not be as much.

I just viewed the Thermo Control web site and the prices are certainly attractive! I'm starting to think that with the $$ I could save on one of these versus the cost of an EKO, Tarm, etc. could be put toward a storage system that I probably could not afford with the latter mentioned boilers pricing. With enough storage wouldn't the Thermo's efficiency be improved and wood consumption/smoke production decreased drastically? I have access to a fair amount of wood for the cost of labor and equipment, so almost free. Taking all costs into consideration it seems to me that the $$ I would save up front on the Thermo would take several years to offset the upfront cost of a Tarm, EKO, etc.?? As an example...let's say the Thermo is $3500 less in upfront costs. I can have delivered barkless oak for $165/cord. Now let's assume the Thermo will use 8 cords/yr. and the other gassers would be half that....that's $660/yr more cost with the Thermo, my break even point is 5.3 years from now. This would be my worst case scenario as I'm sure I won't be paying for wood delivery with the possible exception of the first year....am I missing something here?

Does the Thermo Control actually have a secondary combustion chamber?? Is it a gasifier or just an improved version of a standard wood burner?...just when I thought I had my choice narrowed down I'm back to the drawing board!

From a purely financial viewpoint, gasifiers may not show a quick payback compared to a conventional boiler unless the cost of wood is high in your area. There are a couple of other considerations, though:

1) The near zero smoke and odor is worth something, particularly if you have neighbors nearby.

2) Much as I enjoy cutting hauling, stacking, and handling firewood, I'm not sure that I'd enjoy 8 cords twice as much as I enjoy 4 cords

3) The difference in firewood storage space requirements is worth something as well. All boilers work better with dry wood. Burning less makes it more practical to store wood long enough to let it dry. In some cases, it might allow you to buy green wood for a gasifier and store it an extra year vs. having to buy dry wood for a conventional boiler.

4) Last but not least, the bragging rights are priceless.

nofossil...some good points. My situation is I have no neighbors....I truly would ike to spend less time cutting, etc. but I'm not so busy in my life that it would be a major concern...well at least not until football season! Storage of wood is not a problem as I have space in my barn for this. I would like the bragging rights but actually most of my friends think I'm nuts for going to wood, but I'll bet they will change their tune when they start paying for oil/gas this coming winter!

I'm really torn on this issue.....not a problem physically to cut large amounts of wood at this point in my life and really could use the upfront $$ savings right now. But, thinking ahead I'll bet 15 years or so down the road I may regret not going with something more efficient to cut down on the physical labor end of using wood. On the other hand maybe by then I can use my 401k $$ to buy a really efficient system(and who knows what technical advances will be made by then!) and keep myself more physically fit in the meantime??

Decisions.....decisions

I guess my main question in my mind is would I be better off with a gasser and no storage for the better part of the next 3 years or something like the Thermo with adequate storage immedialty. I really want the true gasser with storage but just can't swing it $$ wise right now.

No one can answer that for you, but it's a reasonable way to look at it. I chose to start with the gasifier and add storage later, but prices for gasifiers were much lower then.

I think the urgency of storage depends on your situation- both the heat load of your house (and its ability to retain heat as time goes by) and what your schedule allows in terms of how often you are willing or able to load the firebox in various situations. If you can run modest sized rather hot burns relatively often (like if you work at or near home or can come home at lunch in cold weather, or if your house will hold the warmth well all day or overnight while you're not tending the fire) then storage seems like it's more about convenience than necessity. If you've got a big-old house like mine that has a thirst for BTUs, and a schedule (like mine) where I can't always plan my timing and whereabouts to tend a fire, and where I really want to transition as much as possible away from oil and to wood, then storage has some big advantages in both convenience and efficiency.

A really financially-savvy acquaintance of mine once observed that it almost always costs less in the long run to get what you really want or think will be best, rather than making do and upgrading later (hidden costs of change-overs, spending $ on things that you then dispose of at a loss, and the fact that what you really wanted only goes up in cost in the mean time). I've seen few situations where he was wrong.

ALL wood boilers, gasification or not, burn more cleanly and efficiently at full throttle. Prolonged idling is a bad thing and will cause the creosote issues described above.

There are three ways to avoid or reduce this problem:

***

2) Build lots of smaller fires, and let the boiler go out when heat isn’t needed.

***

Click to expand...

I'm not sure this fully applies, especially in summer with warmer outside temps and higher humidity. The down periods risk humidity induced corrosion in the system. The firebox is coated with a layer of creosote, and other areas at least have traces of creosote, which is acidic. Water + acid = corrosion. This would not be a problem to the same extent in the winter with lower temps and lower humidity.

Read some earlier threads about TC:
https://www.hearth.com/econtent/index.php/forums/viewthread/18770/

Those are all valid points - the key is that you are making an informed decision!

The TC is not likely to rot out - from corrosion. I think you can count on a 20 + year life span. You are also correct as to the large water capacity and the radiators partially making up for the lack of storage. If it were mine, I would install a 4-way mix valve on the largest and most often used zone - which also adds some "storage" effect.

If everyone took as much time and thought as you did, we'd have more responsible decisions being made. If you can live with the compromises that the TC systems had (and ALL systems have compromises), then surely go for it!

As to the threads here on the TC - many of them have expressly asked stuff like "does the secondary burn really work like the gasifiers" and "is it over 70$ efficient"....that is where education comes in. It is a solid boiler, but it does use 1970's or earlier technology and a buyer should know that. Proper installation, operation, chimney, etc. will go a long way toward mitigating the potential problems......and simple stuff like not using it in the shoulder seasons.

We can also assume that since you are in central maine - that some smoke output will not end up being a big problem (neighbors, etc.).

Grapeview,

I posted in the earlier Thermo Contol threads but thought I would add my 2 cents for you to contemplate upon. 8-/

The first year I had my TC500 I tried to do it without storage and I had a mess. If I ran the boiler flat out with a full load I would have a blow-off because even with a dump zone there wasn't enough water to absorb all the BTU the 500 was putting out. If I throttled it back I got creosote aplenty. It was a lose-lose scenario. I couldn't burn half loads cause I was still a working stiff then and needed 12 hour burns. I don't care what they tell you, you ain't gonna get long burns without creosote! (at least in the boiler model) After I added the 550 gallons it worked like a charm!!

As I stated in the earlier thread I am going to resurrect my TC500 BUT I am gonna use it as a hot air furnace instead of a boiler. I have a center hall colonial so I will plenum it to a grate at the bottom of the stairs. I was thinking this may be the best method for you too. Buy the TC model that is forced hot air and you will be able to get longer burns with no or limited creosote.

I know this is the "Boiler Forum" so I will add that after a few years you can get a gasification boiler and you will better appreciate the less wood you will use.

Good luck,
Gary

grapeview said:

Gary,

How big was your dump zone compared to the rest of the heating area? I forget what you said you used for water storage; was it an oil tank in the basement? Should we be ordering a smaller boiler for our approx. 1500 square ft. of heating space? This is an old cape and we have an unheated upstairs area that could be used as a dump zone (we could throw one or more radiators up there). All in all, this represents a $5,000.00 investment vs. a 10K +++ investment (possibly closer to $12,000) for the gasification unit.



Thanks for your input.

Click to expand...

I want to say right off the bat.....I am no expert on wood boilers....there are plenty of guys here who are better qualified to answer your questions of sizing your boiler and dump zone and storage.

That said, all I can do is tell you what worked for me. I have a 24x36 basement under the main house and had my TC500 with two 275 gallon oil tanks for storage. I did not tap into my oil boiler but instead used the 2 oil tanks as huge radiators. My basement was seldom under 90 degrees. This kept the floors on the first floor warm and I left the cellar door open and the heat would rise all the way to the second floor. I stacked my 8 cord around the oil tanks full of hot water and had kiln dried wood by January.

If you don't use the upstairs area I wouldn't use that as a dump zone because you will be wasting the heat. Maybe use some fin type baseboard in your basement on the walls. Just an idea. Ask the experts for sizing.

I still think that since you have such a small basement you may be better off to just use a plain wood stove for now. That is why I suggested the hot air model by Thermo Control (or any reputable manufacturer). You should be able to purchase one and install it for under $2500 unless you need a new chimney. In a couple years, after you have become an expert , you can sell it and get a boiler.

Good luck,
Gary

Have you considered a Greenwood boiler?

One of the main reasons that I got one is because it has long burn times and does not require water storage. The firebox is surrounded by 4" of refractory cement that allows it to reach gasification temperatures.