EBW200 or 300 with storage?

[robcblair]

I am new to this woodburning stuff and I am trying to decide whether to suggest a 200 or a 300 boiler. Rough heat loss is around 200K but lots of unknowns. Figuring on doing 1500+ gallons storage with either size. Concerned about length of burn times along with storage. Would the 300 burn too fast and have to be feeding more often? Would the 200 work well with extra storage to cover the really cold days? Four (4) different buildings, all with supplemental heat of some kind.

Thanks,

Rob Blair

 

[Singed Eyebrows]

Hi Rob; You want the burn times in a gasser with storage to be as short as possible. Your tanks will store the heat. The longer the wood stays in the chamber the more chance the combustion products have to eat on the boiler plates. I have heard others on this forum say that most of the gas release & burning is done in the first hour with a proper setup & then the coals will heat for awhile yet. I hope my Atmos will burn a full load of wood in about an hour(at least down to coals). Sorry I can't answer your specific Econoburn questions, Randy

 

[stee6043]

Hi Rob; You want the burn times in a gasser with storage to be as short as possible. Your tanks will store the heat. The longer the wood stays in the chamber the more chance the combustion products have to eat on the boiler plates. I have heard others on this forum say that most of the gas release & burning is done in the first hour with a proper setup & then the coals will heat for awhile yet. I hope my Atmos will burn a full load of wood in about an hour(at least down to coals). Sorry I can't answer your specific Econoburn questions, Randy

I'm not sure this explanation of a gasifier is particularly accurate. Your burns will be shorter with storage because you will have no idling, which is a good thing. But the length and quality of the burn depend on many things including wood moisture, draft levels, air settings, etc. and so on. A typical "good" burn for me usually lasts 4 hours with quality wood and good draft. My peak output usually occurs in the second and third hours of the burn...the first hour is spent mostly getting my cold refractories back up to temp.

And the comment about gasses "eating on the boiler plate" the longer wood is in the chamber is...well....I don't think that's true. But I could be wrong...

 

[Nofossil]

Storage is not typically used as you describe - to provide additional heat during periods of peak demand. Instead, it's typically used to provide heat when the wood boiler is not operating.

200kBTU/hr is an extremely high heat load. I hope for your sake that's the peak load rather than the average.

Ideally, you pick a boiler that is just a bit bigger than your peak demand. Any extra output is dumped to storage, Once storage is up to temp, the boiler is allowed to burn out. You then heat from storage until storage is nearly depleted, then repeat the cycle.

If your boiler is sized for peak load, then it's output is more than twice your average load. That means that on an average day it would only need to burn for less than 12 hours - in my case, the average daily burn is 7 hours.

 

[Birdman]

Nofossil. Will you comment on the part of the comment from the beginning of this post post?


"The longer the wood stays in the chamber the more chance the combustion products have to eat on the boiler plates."

 

[Singed Eyebrows]

As Stee says burn times depend on quite a number of things. My Atmos requires very dry wood 12 to 20 percent max & a draft that is capable of supporting 70 percent of boiler output on electric power failure. I will not need to cook off much moisture as others might. I guess others may disagree on getting the wood burn't out as soon as possible, the engineering treatise on You Tube doesn't. I too am interested in Nofossil's opinion on burning the wood as hot & fast as possible to minimize corrosion. I am assuming the Econoburn & Stee's EKO need to be run mostly like my Atmos & maybe this is incorrect on my part. Randy

 

[Piker]

Pit,
If your heat load is really 200,000 btu at design temps, then a 200,000 Btu boiler will not have any excess energy left over to store into the tanks... at design temps. The less excess Btu's you have to put into the tanks, the longer per day you will have to run the boiler to charge the tanks. This is great for efficiency, but it might make it difficult to actually get the storage up to temp in a practical time frame. For the most part, I think it's best to run your calculations based on no more than an 8 hour burn on the boiler to charge the tanks on the coldest day. This equates to about 2 loads of wood through the boiler.

Always remember that solid fuel appliances do not have static output. There are many many factors that affect output... too many to list, though someone mentioned a few above. I know that Econoburn boiler Btu ratings on the residential models are average output ratings based on a decent sized percentage of the burn curve and centered over the hottest part of the burn. The maximum output is actually significantly higher than what is published. This is of course under lab conditions, and will vary from one burn cycle to another depending on all the variables that we didn't mention before.

If you have any questions, you are more than welcome to call me and pick my brain for thoughts and ideas.

cheers

 

[Piker]

As Stee says burn times depend on quite a number of things. My Atmos requires very dry wood 12 to 20 percent max & a draft that is capable of supporting 70 percent of boiler output on electric power failure. I will not need to cook off much moisture as others might. I guess others may disagree on getting the wood burn't out as soon as possible, the engineering treatise on You Tube doesn't. I too am interested in Nofossil's opinion on burning the wood as hot & fast as possible to minimize corrosion. I am assuming the Econoburn & Stee's EKO need to be run mostly like my Atmos & maybe this is incorrect on my part. Randy

Hot and fast does a couple of things. 1) it reduces the amount of particulate matter (creosote) that exits the boiler through the heat exchanger by burning it before it gets there. This is critical on a unit like the Atmos which I believe has draft induction as opposed to forced draft. Daft induction units tend to plug up the draft inducer fan with creosote if left to idle too much, while forced draft units don't have this issue. You still have to be careful what you burn and how you burn it when you run a forced draft unit without storage, but they are a little more forgiving. Not saying one is better than the other here, just pointing out the differences. 2) it also reduces the potential for condensate to form in the boiler. By keeping the boiler in gasification you maintain temps throughout the combustion chamber and heat exchanger that will reduce the possibility that water droplets can form, mix with the acidic ash and soot, and cause corrosion.

I think that a well built boiler without storage should last 20 to 25 years if properly operated and maintained. If you run with storage, I would think you could add a few years to that figure.

 

[Gooserider]

What I've seen suggested as a sizing rule of thumb is to pick a unit one or two notches above your peak demand...

The current Manual J on our house gives a "design day" demand of about 88KBTU/hr - the next larger size for most companies is around a 100KBTU/hr unit, however several suggested that I would be better off going to the next size up, 120-140KBTU/hr... That way even on design day, I still have some reserve heating power if I need it, and will still be able to charge my storage fairly quickly.

The other suggestion is to size the storage such that you could theoretically take the storage from "minimum useable" to "maximum operating" temperatures on one full load of wood, assuming nothing else is drawing on the boiler output, and that nothing else is trying to heat the storage... By having this much "BTU acceptance" capacity, you minimize the chances of overheating, or forcing the boiler to shut down before it has fully burned the load of wood...

Gooserider

 

[Nofossil]

Nofossil. Will you comment on the part of the comment from the beginning of this post post?


"The longer the wood stays in the chamber the more chance the combustion products have to eat on the boiler plates."

I haven't seen this particular issue. However, prolonged idling does result in decreased efficiency and increased creosote. In some cases, the lower stack temps during idle can lead to condensation, which could cause corrosion problems.

I believe the biggest contributor to corrosion is water inlet temperatures that are too low. Most boilers have some sort of inlet temperature protection too keep the incoming water about 140. I suspect that if you have marginal water inlet temps that idling could result in corrosive condensation in the boiler.

 

[Singed Eyebrows]

There has been an issue here with my stating the longer wood stays in the chamber the more chance it has to "eat" on the plates. In rereading this it looks like I was hungry at the time. The wood itself does not eat the plates as I thought everyone understood, it is the acids produced as Piker explained. I should have been more accurate as wood that has the moisture driven out of it can certainly sit in the boiler without much damage. My approach with my Atmos will be be to keep the boiler temps up as Nofossil says & I'm going to get the wood/moisture out as soon as possible because I'm pretty sure burning wood is not good for the health of my boiler, Randy

 

[Gooserider]

There has been an issue here with my stating the longer wood stays in the chamber the more chance it has to "eat" on the plates. In rereading this it looks like I was hungry at the time. The wood itself does not eat the plates as I thought everyone understood, it is the acids produced as Piker explained. I should have been more accurate as wood that has the moisture driven out of it can certainly sit in the boiler without much damage. My approach with my Atmos will be be to keep the boiler temps up as Nofossil says & I'm going to get the wood/moisture out as soon as possible because I'm pretty sure burning wood is not good for the health of my boiler, Randy

My take on it is that as long as the boiler temperature is kept high enough to prevent condensation, then burning wood in the boiler isn't particularly damaging to it, regardless of how long it takes - arguably since metals seem to generally oxidize and break down faster with higher temperatures, one would optimally want to burn at as low a temperature as was consistent with avoiding condensation, and keeping the secondary combustion going so that the smoke byproducts are consumed... At any rate, it seems to me that the reccomended normal boiler temperatures don't lead to significant damage issues...

Now obviously if one burns a boiler at all, it will last a shorter time than if it was kept unused in it's sealed factory packaging, %-P but defining "normal useage wear" is a bit trickier... Me I figure 20-30 years is a reasonable life expectancy. Who knows, by then we may all be heating our homes with our handy dandy "pocket size nuke-reactor pack" and won't have to worry about this wood stuff in any case...

Gooserider

 

[Como]

I am in a similar situation but with twice the peak load.

If you are looking new then there seems to be only one of each left?

I am looking at a Garn, I could justify the biggest one, but it is twice the cost of the 2,000 (why?). SO I will get a 2,000 and am hoping I will be able to leave space to add another IF I need it.

We do get massive temperature fluctuations, at all times of the year, I am considering that for the few days we are at maximum demand, then either I shut down part of the building, or we supplement with an existing wood stove and our back up, yet to be decided. Or we are just a bit colder.

 

[Singed Eyebrows]

Every time you burn wood in your boiler you degrade the plates, more or less. To say that the wear is almost non existant or that somehow your boiler is not affected by this is incorrect in my opinion. It's there, it just takes awhile to show up. My Atmos has a 10 year life if operated properly. I was told & I believe I read a carbon steel Woodgun has a 10 year life. Each of these can exceed this under the right conditions. Even though you keep the boiler temps up you will still degrade the plates, it just takes longer. I don't attempt to make my points with funny faces & I feel the ridicule is beneath what is otherwise a classy poster. My original reply was to try to help a fellow Hearth member & I stand by what I said. Next! Randy

 

[Piker]

There is a difference between degrading the steel due to corrosion caused by condensation, and degrading the steel due to heat, thought the two can be closely related. One of the biggest issues regarding gassifier life is what you do with the heat produced by the gasification torch. If there is little or no refractory material of some sort to absorb and evenly disperse the heat of the flame into the surrounding steel and water jacket, the steel is going to burn out quickly, and there goes your investment in a relatively short period of time. This is of particular note when talking about the doors on a gassifier, especially the bottom one. There is also the issue of the quality of the refractory itself. Not all refractory material is created equal, and while your boiler may last "X" amount of years, your refractory may last only a couple years if it's the cheap stuff. I believe nofossil has expiremanted with some different materials for channeling the heat in his combustion chamber... many of the materials he tried turned to dust in a very short period of time.

cheers

 

[Gooserider]

Every time you burn wood in your boiler you degrade the plates, more or less. To say that the wear is almost non existant or that somehow your boiler is not affected by this is incorrect in my opinion. It's there, it just takes awhile to show up. My Atmos has a 10 year life if operated properly. I was told & I believe I read a carbon steel Woodgun has a 10 year life. Each of these can exceed this under the right conditions. Even though you keep the boiler temps up you will still degrade the plates, it just takes longer. I don't attempt to make my points with funny faces & I feel the ridicule is beneath what is otherwise a classy poster. My original reply was to try to help a fellow Hearth member & I stand by what I said. Next! Randy

That could be said about oil and gas boilers just as easily, or fireplaces, and so forth - if you burn ANYTHING in a vessel, you presumably shorten it's life; by how much is a more complex question. I never said anything different. My opinion is that attempting to keep the temperatures of the metal as low as practical without going below the condensation temperatures, and consistent with maintaining secondary combustion will maximize the boiler life. There are also definite design factors to consider, as Piker mentions. (Among other examples see some of the threads on the recent Central Boiler failures due to exposing the steel to high temps in the gasification burner area - this appears to be a heat failure issue, not a condensation problem.)

Now I am not throwing stones at the Atmos, or the Carbon Steel Wood Guns, but I have gotten a distinct impression from what I've seen of the units, and their respective websites, that both are constructed as "economy" model boilers (especially the Atmos "G" models as opposed to the "GS" models) WG claims their stainless models have a 25+ year life expectancy, as in their oldest stainless models have been operational for that long... (This despite the way that the WG operating instructions encourage idling, which the other makers say has a bad effect on boiler life) Some of the other carbon steel boiler companies have been talking life expectancies in the 20-25 year range, when operated properly. Thus I wonder if the issue you seem to be suggesting with the Atmos is more due to the brand of boiler than it is the fact that it burns wood...

Another question that may also be relevant is what the "failure mode" is that causes these boilers to be replaced? Is it a failure of the boiler vessel or heat exchanger tubes? Or is it a question of other parts failing that are not worth repairing? Or is it just a general need to update, similar to the urge to turn in reasonably functional cars on newer models?

If it is a failure of the boiler vessel, then yes your question about steel degradation is an important one, since it has a direct impact on the boiler lifespan.

If the critical failure is in a different area, then steel degradation is somewhat of a non-issue since the boiler vessel outlasted the rest of the unit - just as putting a one million mile grade engine in your car won't increase it's life if the frame rots out at 500Kmiles...

This is a topic I haven't really seen addressed that much - perhaps some of our industry pro's can chime in and tell us what it is that is most likely to be doing in our boilers?

Gooserider

 

[Singed Eyebrows]

Hopefully I'm not too far off Robs post with this reply. The Atmos does not have a firetube exchanger & this was somewhat of a dissapointment. This has a simple exhaust gas passage in the boiler back with plates welded to a water jacket. Whether this can achieve 81 to 87 percent efficiency as advertised, I don't know. I would be very surprised to see a failure in this area. In the Woodgun the failures I read about & Patrick explained to me were in the primary chamber. I believe it was Fred61 that talked about patching up his Eschland/Woodgun & I cant imagine that he ground off the welds & pulled the firetube exchanger. The plates in the old carbon steel Woodguns were capable of being eaten up I believe by acids in a very short time. Piker's post was very interesting as usual, I was not aware of the wear & tear that the torch flame could produce. Woodgun is under the impression that their boilers failed because of gasket leaks. The carbon steel Woodgun must go into idle with airtite doors & power intake etc, or it will fail from acid attack to the primary chamber plates. I was concerned that Rob was going to attempt to run an Econoburn like a OWB & that is why I posted as I did. I'm far from being the expert that I feel Piker & Nofossil are, I'd like to think I have a little common sense though & I felt that if water was prevented from combining to form an acid, then you would no longer have an acid. If I have corrosion trouble with my Atmos I have a flame sprayer that I can put a chromium etc coating on it. It would be nice if expensive gassers had something like this. The expensive Lamda boilers fight corrosion with hot plates & these should take care of much of the acid attack & torch flame all in one shot. Randy