I have a Franks Piping Boiler in my basement that I bought with very little use twenty years ago. It supplies water through a secondary circuit to my radiant floor through tempering valves. The boiler water is maintained at 180 f. In general it has performed well but sometimes smokes heavily and creosotes my interior lined masonry chimney. The smoke in this rural area bothers only me and I clean my chimney at least three times a year, probably should do more. I would like to do better. I believe that the smoke and creosoting is due to the fact that the intake damper door, controlled by an aquastat and Honeywell controller is either all the way open or totally closed. Roaring fire > 180f > closed. I have just become aware of a Samson controller which I think (never seen one but on a screen) has a more progressive action similar to a bimetallic stove damper. Can someone confirm this? Would the adaptation of this damper controller help my situation. Thanks for any advice on this.
Modify a Franks Piping Boiler
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I can't say much about your controller question but I guarantee your creosote is coming from the fire being choked down by the damper. That's what we call "idle mode" or idling. It's just as you described roaring fire then damper closer and snuffs it too a smolder. Smoke is the result. Smoke condenses on interior boiler walls and chimney...creosote.
Warno, thanks for the reply, I know that the abrupt close of the damper door causes creosote. I have been outside the house to see the foul smelling smoke roll out of my chimney. I have considered scrapping this boiler, but perhaps I can improve it's function. Why was this on/off damper design used when this unit was built. Why not a gradual on/off Samson? This is a wet base old fashioned boiler I know it will never burn as clean as a gasification type.
No direct experience by I believe by adding correctly sized storage you will be able to run that boiler wide open and do batch burns. @peakbagger has done this with a burnham boiler with good results. Only downside is you have to have space for ~400-800 gallons worth of storage tank(s) and some added complexity.
Would the air damper control just slow the open/close or would the idea be to hold the damper only partially open to slow the burn?
they probably used it because it's simplicity. Simple mechanics, simple controls. Even if it was a gradual closing of the damper it would still idle and smoke at full close. Now if it choked it down but still maintained a slow burn, not smolder, then you'd probably be ok. But even a slow burn is making heat so the control system might be tricky.
That's my thought, a slowed burn that is still clean is going to add significant heat and with out storage how are you going to manage that in low demand situations.
I don't anything about the design of this particular boiler, but if it has a firebox surrounded by water I suspect there will be no such thing as a slow clean burn anyway.
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Yup that is my install. I inspect the chimney every year and run a brush out of guilt every 5 years or so. I have the same damper setup, its either full on or full off. My configuration is a bottom grate feeding into triangular refractory pit where the wood goes and then water jacketed fire box with baffle plates about a foot above the refractory pit. Above the baffles are a lower tube sheet with 16 or 20 tubes that then empty into an upper ash chamber before it vents out the side. It has half burnt off turbulators down the tubes. Its an ASME coded boiler and was built beefy. It was coal/wood rated for 85,000 btu/hr input. I have 500 gallons of unpressurized storage.
My wood boiler is in series with an oil boiler. If the storage is over 140F , the oil boiler burner is locked out but the circulator and zone controls are working using water from storage. I have 550 gallons of pressurized storage good for 185 degs max. Therefore I can store about (185-140)*8#s/gallon*500 gallons = 180,000 btus which is the equivalent of 2 gallons of #2 fuel oil fied at 87% efficiency. The boiler itself probably has 80 gallons of storage plus 1000 pounds of mass so when its heated up, it releases heat slowly to the basement and up through the main floor. I get around 24 hours between firings, double that during the cold windy weather of the last two weeks. I am short on radiators so wen its really cold 140 F water really doesnt cut it so I tend to fire it more often by shorter runs.
The boiler is in series with an oil boiler, if the storage is below 140 degrees the oil boiler takes over like the wood boiler isnt there. Once the storage is over 140 F the oil burner is locked out with fail close relay. I then start the wood boiler up. there is circ pump that pumps water from the top of the boiler to the bottom, the pump is off until a thermoswitch mounted hald way up the water jacket gets to 140 degrees. The pipe that discharges out of the boiler goes to three way motorized valve that fails in one position. Normally the water circulates to the top of the oil boiler and to the bottom of the wood boiler. If there is demand from the zones it pulls the hot water one way or otherwise it goes back to the wood boiler. One the temps up a bit I flip a switch and the three way valve switched to the coil in the storage. It will keep heating the storage until a thermoswitch hits a high setpoint and then the three way valve switch back to recirculating. If there is no heating demand the damper shuts and my dump zone rapidly comes on.
This means I have about three to four hours to bring the storage up to temp. With a bottom grate, I can really put the wood to it and it burns fairly clean as it has all the air it needs and the refractory pit really concentrates the heat. I feed it about every 20 to 30 minutes with maple and birch because that is what I have, I have on rare occasions got my hands on oak and it definitely burns longer. Once the storage get up around 175, I start to taper off a bit on the wood. If I time it right the fire goes out just about 185 storage temp. I then flip the a switch and the controls and piping switches to pull heat out of the storage and manually close the air damper. I also can put it in an in between mode which I accidentally wired up that allows me to heat the house off the extra heat in the wood boiler. The bummer is I need to wake up and switch it out of this accidental mode or eventually the oil boiler turns on. I normally just switch it over heating off of storage after the fire is out. I then have hot boiler that circulates around and around and some of the heat leaks past the zone checks and zone pumps putting heat into the zones. Between that and the hot mass of the boiler, on a cold night it take four of five hours before there is heating demand. I have a hot water heater zone that runs to a superinsulated "hot water maker" that I charge up to about 170 degrees, I use a flat plate solar hot water system to preheat the incoming water to the hot water maker so it lasts quite awhile usually 24 hours before I need to heat it up again and I plan my major hot water use around the wood boiler. Once the boiler temp goes under 140 the circ pump shuts off. The boiler usually stays quite warm to the next night when I fire it again. The only real hassle is I have to relight a fire every night as there are no coals with bottom grate. Its doesnt take much, I either use birch bark or news paper under the grate from the ash pit and then put a couple of squares of card board and kindlng on top of the grate. Light the newspapers and since the boiler is warm it has plenty of draft and its roaring in about 10 minutes.
My controls are all hard wired with relay logic and everything is setup that if the power is off to the wood boiler, the oil boiler works like any other oil boiler and if I am not home and the storage temps drop below 140 the oil boiler skips the storage and heats the house normally. If I wanted to go PLC I could put some higher level logic with timers and make things even more automated but this works for me. I could really clean up the piping and put in some hydraulic separators but hard to spend money on a house that burns 2.5 to 4 cords a year. I use an electric mini split for shoulder seasons run off "free" net metered solar power but before the mini split I might have used 4 to 5 cords.
It all comes down to how quickly can you get the heat out of the wood boiler and into the storage. I have 1" piping coming and going to the coil and the three way valve is a large port valve. If I am really pushing the boiler hard and stuffing it full of large dry maple logs, I can over run the capacity to pull heat out of the boiler fast enough, its borderline and I have modine type heater that I can turn on to dump heat or if I dont notice the damper shuts and the dump zone kicks on. I expect I might be able to push a bit more water through the loop as I just installed what I had for a circulator pump. I expect if someone had a larger capacity boiler they may need to get two coils into a larger tank.
My neighbor tried to heat his house with a wood boiler without storage, after numerous chimney fires despite near monthly cleaning, a cracked flue, a melted liner he finally gave up and went with an OWB with a 30 foot stack and huge wood pile. He was skunking out the neighborhood with a short stack and just had to keep extending it until it was tolerable.
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