Wood boiler efficincy

JackFre

The old rule of thumb for burning wood is that if you burned it for only the 30 coldest days of the winter you would save 50% of your heating bill. The advantage of putting this out to the wood burner is that they frequently try to run them every day and they just lug along, making soot, creosote, CO, smoke etc. Ultimately this lugging/inefficient operation creates equipment reliability issues too.

Build a fire, let it burn hot and you can do pretty well.

Steve Ebels_3

Wood boiler effiency

Lot's of you guys in the cities have probably never seen one of these but they are very common and getting more common every day out here in the country. I serve as the clerk for our township and as such I get input and/or feedback from local folks regarding a lot of different issues. One of the complaints that I have heard several times is the amount of smoke emmision from Outdoor Wood Boilers (OWB). I have been searching for some organization or standards setting body that might have some research on these products and I finally found someone who does.
He's from the Michigan DEQ air standards division and in a recent phone conversation with him he told me that he had one tested in a lab just a month ago. (they are all pretty generic in terms of operation and construction) I had guessed that these things would maybe hit 40% efficiency but the lab results indicated the top number being 34% with the average hitting less than 30%. That's with a clean unit operated under lab conditions with properly seasoned wood. The lab, which was in Madison Wisconsin estimated that under normally encountered field conditions, efficiency would run from 20 to 30% max.
The particulate matter, and Carbon Monoxide emmisions were literaly off the chart of any type of normal combustion.

Why am I posting this info? Just so that people who have one or are contemplating purchasing one of these (OWB's) are aware that,

A: they pollute like crazy

B: If you have neighbors closer than 1/4 mile they will hate you

C: If you have to buy your wood you'll probably never get a return on your investment before the OWB kicks the bucket.

Standards are being written as we speak that are going to drastically effect the manufacturers of these things. Draw your own conclusions to that

E: The only wood burning units they anticipate meeting the new standards are gasification type units

Just food for thought.

hr

Only the downwinders

will complain Although at some point we are all down wind, just as we are all downstream from water pollution.

I agree more and more folks are shopping wood burners.

I believe the standards, at least from the EPA side of the fence, are already set. Not yet accepted or enforced state by state. Much less town by town.

A lot like building and mechanical codes WHO will enforce them, and how! Under what budget?

I have also talked with players in the industry. One lab that has tested many brands over the years claims that 40% plus or minus is the average.

BUT, the catch is how well they are burned! I suspect rarely are they burned to lab conditions, in the field (pun intended)

Not only does wood species, quality, moisture content, etc play into it but how well the fire is tended to keep it burning hot and efficient.

I doubt that any brand, of any type, including gasification, can be fueled, lit, and walked away from for the day and expect a clean efficient burn all day.

You need to maintain a fire bed, poke it, adjust it. Just like a camp fire.

My experience with a few gasification units over last heating season is they are only efficient and clean burning when they are in the gasification mode.

They are as finicky if not more so, than a plain old OWB when it comes to keeping them in their "sweet spot" You really need dry wood, at least a year drying. Many Euros sell moisture meters with the stove, for this reason.

They need to have a return water temperature hot enough to keep them from creasoting up. This leaves you with a fairly tight operating range, maybe 150- 180 considering the use of pex tubing and it's high temperature limit. Plenty of connection meltdowns every year as the fires "get away" from newbies

I suspect the tiny fuel boxes are for a reason, in that it forces the operator to better maintain and fuel them. A far cry from large American brands that will accept a small car inside

Burning wood is an operator intensive task, far from gas or electric energy useage. At least at the homeowners end of the equasion.

I believe a handful of the OWB manufactures have started a small association, or task force, to determine how they will deal with these strict, but important in my opinion, emission requirements. I'm watching closely also.

hot rod

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David_5

Boiler size

The ones I have seen have very large btu capacities even on the smallest sizes. This means they will be likely oversized even on design days, never mind spring or fall. I put a wood coal boiler in my house 15 years ago. The capacity is 80k output. That is still large because my oil boiler can do the job with 95K output. 0 degrees is a design day for me. A wood boiler should probaby be sized to be a max ouput at 20 degrees and the oil making up the difference. This way for alot of the year the boiler would be burning full bore, the way they should. In my house I quickly found out burning wood was more trouble than it was worth. I switched to coal and found it to be easier to control, better output, easier to store, and cheaper.

David

Lloyd Nichols

Various regards wood boilers

In the interest of sharing info about this subject I thought I might reply to the above postings. What else is there to do on a rainy Saturday night anyway??

Yes, more and more people are shopping for wood boilers to try to keep their cost of heating homes and businesses under control. If fossil fuel prices stay at current levels it is a good bet that interest in wood heat will continue to grow, as long as it is done in a responsible, earth friendly way. In regards to emissions from wood heaters, there are EPA regs. that apply to freestanding wood stoves. Many people think that these regs. also apply to wood boilers and furnaces. However, wood boilers are specifically exempted from these regs., as are a number of other types of wood burners. There are currently no emissions regulations that apply to these units like for wood stoves. Unfortunately, in a few cases some states and county regulations require that wood boilers meet the EPA emissions regs. which specifically do not apply!!! It is a serious problem for people in those locations who want to install a wood boiler. Even if there was a zero emissions boiler available it can not legally be sold where the local regs. require the (non-existent) EPA approval. No amount of money can buy an EPA approval for a wood boiler. It's a bit of a dilemma for those of us in the business. Just today I had to tell someone in Tacoma, WA that we can't legally sell them a wood gasification boiler without risking fines and jail time!

As regards OWBs, there is an ASTM Task Group (I'm a member) working on development of a test protocol to be used to test the emissions and efficiencies of Outdoor Wood Hydronic Heaters (OWHHs). (Most of the outdoor water stoves are not boilers, thus the reason for renaming to OWHHs by the ASTM Task Group.) The test results that Steve referred to above are from the first of many tests that are to be run to determine exactly how these units should be tested to give representative, repeatable results. The reasons why this is being done are because of the many reasons already stated above by Steve and Hot Rod.

Now, in defence of the wood gasification boilers which we sell, use of dry wood and a heat storage system matched to the boiler results in a very easy to use wood heat system that gives high efficiency and very low emissions without poking and adjusting. They are not finicky. Yes, there is more personal involvement but the rewards are well worth it for some people. Many of our customers only load wood into their boiles once or twice a day. Not for everyone maybe, but, as the pain of $400 to $800 per month bills for heating oil and propane gets more severe some people will look for a good alternative. I think Jack has it right. I would just add heat storage as the way to get increased efficiency and utilization of wood energy.

David mentioned above that he swithched to coal. We are seeing interest grow in our wood pellet and corn fired boilers. They offer automatic firing and can typically go a few days between fuelings. They can also be installed with fully automatic fueling from a bulk storage bin or silo. We have one company heating a 46,000 sq. ft. manufacturing building with wood pellets. This stuff is not only lots of fun but it is important if we are going to get serious about the coming petroleum fuels availablity problem. We can make a difference. We just need to do it. The "Eco-Economy" is here to stay. 'Leastwise that's the way I see it.

Lloyd