In the interest of full disclosure, the author is a Director of Maine Energy Systems, in Bethel, Maine.
As one of the leading developers of the residential biomass heating industry in the United States, we’ve learned a lot of lessons along the way. As the owner and operator of a pellet-fired residential boiler system, I’ve learned a lot of lessons along the way as well. Following are a few of the lessons we’ve learned.
As I’ve reported in earlier blogs, my large, old farm-style house in Bethel, Maine, was heated experimentally last winter with a four-section pellet-fred boiler. The Janfire-fired system is rated at 23 kilowatts, about 51,000BTU/hour. The system heated the house to our satisfaction pretty well last winter with the exception of a few “design days” when outside temperatures dropped below zero. On those days, we were faced with a house at, or below, 60 degrees F, or burning a bit of oil to support the pellet boiler.
During this past Christmas seasons, my 86 year old mother joined us for two weeks. Our standards for suitable heating (67F, or so) didn’t work for her, so we needed to try to keep the house at 70F at a minimum. The little boiler fired at capacity much of the season to meet the demand and was generally successful. However, on days when single digit to sub-zero temperatures struck, there was no way. The boiler is just too small to fill that demand largely due to heating time lost to the ashscraping cycle of the top-fed burner. To meet the need, I set the oil boiler to fire when water temperatures dropped to 160F. All worked well; the boiler fired occasionally, generally following an ashscrape cycle when water temps would drop below the target level. My mother was warm and little supplemental oil was burned. During the past heating season, I used a total of 40 gallons of supplemental oil.
It is my assumption that a small boiler of the same capacity of an underfed burner design that did not require lost time to ashscraping would meet my demand without support from the oil boiler. It would be fun to test the assumption.
Because I’ve been able to use an extended ashscrape cycle due to the improvements in pellet quality, I haven’t been cleaning my boiler as often as I did last year. That’s been a mistake. In this particular Bosch/Janfire system there is ample opportunity in the cast iron boiler for ash to reduce boiler efficiency. I’ve returned to a two week cleaning cycle for this boiler to keep efficiency up and pellet consumption down.
In the interest of full disclosure, Dutch Dresser is the Managing Director of Maine Energy Systems which sells both the Bosch/Janfire system referenced here and the more advanced AutoPellet systems made under license from OkoFEN of Niederkappel, Austria.
In the interest of full disclosure, Dutch Dresser is a principal of Maine Energy Systems in Bethel, Maine. Maine Energy Systems distributes the Janfire NH burner discussed in this post.
As those who’ve read my posts will know, I’ve enjoyed my MESys 4000 system this past winter, and I have experienced no significant issues with the Janfire NH burner that fires the Bosch cast iron boiler. Nonetheless, others have experienced different issues with their systems, so all burners in the field have been receiving a system reconfiguration this spring to eliminate known weaknesses. I had my burner done last week, one of the last to receive this reconfiguration.
Peter, the Bosch tech, removed the burner from my house, took it to our MESys facility, and performed the necessary reconfiguration. This included a full inspection, the replacement of two temperature sensors, one in the drop shaft and one in the burner bowl, and the installation of new processor software.
Once the burner work was complete, Peter gave my boiler a thorough cleaning, including the flue vent. While cleaning the boiler, Peter discovered that the refractory insulation in my boiler door was cracked, so he replaced it. He also ensured that there was plenty of insulation above the burner aperture. This reduces heat to the drop shaft temperature sensor. It is that sensor that would detect any burn back issues, so keeping it cool prevents any false positive readings.
Any reluctance I’d felt earlier to having the burner modified, I soon lost. Peter did a great job. The burner continues to operate beautifully for me, and seems to spend even more of its time in either “keep alive” or “waiting” mode now that it just heating domestic hot water. I’m anticipating somewhat lengthened cleaning cycles this summer.
I continue to find the transition from oil to renewable, locally produced fuel for heating my home a satisfying experience.
Dutch Dresser
Summer has arrived in Maine at long last. Temperatures have risen into the 80’s and all is well, but the pellet boilers need to be “summerized.”
As temperature differences between my basement and the outside air have converged, I’ve begun living with a continuous “low chimney flow” condition and the associated red indicator light on my Janfire NH burner. I have cleaned the breach of the boiler and the flue pipe, and I always keep the boiler free of excess ash. I have the boiler on an independent chimney, which, as our technician puts it, “would suck your hat off.” The chimney rises well above the house. (June 1, Alas, the “low chimney flow” error was a legitimate problem, my baffles had fallen over the burner bowl. Realignment of the baffles resolved the low chimney flow condition. The baffles tend to “gain weight” as combustion by-products adhere to them; they are scheduled for redesign by Bosch.)
To confirm that the light was indicating an actual overheat condition at the drop shaft sensor, I checked the
As the summer demand for heat changes to domestic hot water, only, systems with very little heat loss in the piping might need to have their minimum boiler temperatures reduced to avoid unnecessarily high boiler temps. In my own case, about 60′ of 1 1/4″ copper tubing leading to and from my oil system “wastes” heat into the basement elminating any such need. In the winter, I appreciate that extra heat in the basement; now, I’m likely to put insulation around the pipes to keep it out of the basement.
Dutch Dresser
Dutch is a Director of Maine Energy Systems in Bethel, Maine.
I enjoy learning about my new boiler, so I check on it often. At work, I can hear a MESys 6000 all day as it heats a substantial part of our office/warehouse building. Because of that exposure, I’ve come to know by sound when things are different than they should be.
A couple of weeks ago, my boiler didn’t sound right, but I ignored it. A day later, it failed with a “flameguard overheat error.” When I opened it, I found that I hadn’t put the baffles in properly when I cleaned the boiler and the baffles had fallen over the burner. I took out the ash, replaced the baffles and was back in business shortly.
This morning, I heard the oil boiler come on, which shouldn’t happen, even with my purposefully undersized boiler, until outdoor temperatures are well sub-zero, and this morning’s temperature was approximately 10F. I went to look at the boiler and it was “working,” but it didn’t sound right. I looked through the inspection port and, sure enough, a baffle was standing edgewise next to the burner. Again, I hadn’t done well replacing the baffles after cleaning.
I opened the boiler, took out a few shovels full of ash and carefully put the baffles back in place. I find the balance of the baffles a delicate one, particularly as the baffles become a bit heavier due to combustion product deposit build up.
During the next cleaning I’ll remove some of that build-up on the baffles to see if it makes it easier for me to get them properly installed. I’ll also attend to the shortening of the baffles that has been recommended for the four-section boiler; both of those steps should help make the possibility of misaligning the baffles after cleaning less likely.
Dutch Dresser
Until you begin to understand all the variables associated with ash cleaning intervals in a pellet fired boiler system, the question, “how often do you have to remove the ashes?” seems simple enough.
I decided to test my MESys 4000 boiler to point of failure by not removing ash until a “Problem! Low chimney draft” error indicated it was shut down due to the problems of ash build-up. Through a couple of test cycles, it became clear that around .8 tons (1600 pounds) of the pellets I’m using would create enough ash to fill the boiler enough to shut it down. By test, we know that those pellets contain 1% inorganic ash; so, my system can handle 16 pounds of ash before a cleaning out is required.
My boiler is purposefully undersized for my house, yet it has managed to carry the house’s heat and domestic hot water demands even into this week’s sub-zero weather. This morning at -12F in my backyard, boiler water temperature was at 177F when I checked it at 6:00 a.m. To provide this heat for the house, I am burning approximately 100 pounds of pellets per day. That means that I should plan to clean the ashes out of the boiler every two weeks during this weather in which the burner is running at maximum output full time. (I clean it every other Sunday; it takes a half hour.)
The MESys 6000 boilers are using roughly 120 pounds of pellets per day when they are in full fire conditions. They will handle 40 pounds of ash or more between cleanings. That means that regular cleanings for those boilers should be scheduled approximately every 30 days if they’re operating under full fire conditions using pellets that generate 1% ash.
The last qualifier is important. Pellet ash content varies among manufacturers and even among mill runs. Pellets produced and tested to PFI (Pellet Fuels Institute) standards that are labeled “premium” will contain inorganic material to produce 1% ash, or less. It’s not uncommon for pellets to have 0.5% ash, which would double the cleaning intervals.
Some of our boilers are in the Arctic Northwest, and the pellets there are so clean that ashscrape cycles are set to the available maximum setting of a scrape every 144 pounds and, even then, the scraping is unnecessary, and ash content of the pellets is at, or below, 0.3%.
Dutch Dresser
In the interest of disclosure, I am a Director of Maine Energy Systems.
After burning 0.64 tons (1280 pounds) of Energex pellets according to the data made available by the Janfire NH burner on my system, I decided to remove the ash today to begin to get a baseline for proper ash removal intervals on my MESys 4000 system. The burner’s measurement is based on fuel density entered by the user; I entered 42.1 pounds/cubic foot based on weighing of several samples. An error in this setting would yield erroneous consumption figures.
In lab testing, the pellets I’m burning are reported to have 0.75% ash content, therefore, I was expecting approximately 9.6 pounds of ash. I opened the top and bottom doors of the boiler exposing the top of the cast iron core on the top separated from the lower chamber by removable baffles. After removing all the ash from the boiler, I weighed 12.6 pounds of ash, or nearly exactly 1% ash.
The bottom of the core was about half way up the bottom door with ash space below it. I found a small amount of ash on the cast iron and atop the baffles in the top section. I found a pile of clinkers below the burner resting on the inside bottom of the core, and I found talc-like ash in the bottom of the boiler enclosure. The clinkers were most interesting to me as they are the physical evidence of relatively low ash melting temperature (1250C) inherent in the pellets I am burning. We had been told of this attribute by the Swedish testing labs used by the burner manufacturers.
While the clinkers cause no issue for the burner or the system, they did keep some of the fine ash from falling to the storage area on the bottom of the boiler enclosure. Until regionally produced pellets have sufficiently high ash melting temperatures to resist the formation of
clinkers, I will open the top door and remove the clinkers every half ton, or so, to allow for reasonable ash storage in the base of the system. After burning nearly 1300 pounds of pellets, there was ample room in the base of the boiler for lots more ash in this four-section boiler. The ash from more than two tons would have easily fit in the storage bin at the 1% volume, I discovered in this ash removal.
The recommended ash removal interval for the six-section boiler is every three tons of fuel; I’d be perfectly comfortable allowing 2.5 tons of fuel to run through this four-section boiler before removing the ash. However, the whole cleaning process, including opening the boiler, cleaning, and closing the boiler took me only twenty minutes, so I’ll likely empty it more frequently just because it’s easy.
Dutch Dresser