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Dump zone plumbing ideas

leonzleonz Member Posts: 329
Since I am home bound for a while I wanted to examine dump zone ideas for my coal stoker boiler.
I have used Dans tried and true pump module with an Internal Air Separator , Airtrol Valve and a steel compression tank and I have one open tapping on the end of the boiler steam chest that is 3/4" NPT and it has a 6 inch pipe nipple and pipe cap in it now.

I have asimple system with 225 foot of 3/4 fin tube baseboard and a honeywell mechanical triple aquastat set with 150 low 170 high and a 10 degree diferential and a honeywell dump zone aquastat in the steam chest that turns the circulator on when the 200 degree high limit is reached with a ten degree differential and as it happens quite often in the warmer parts of the heating season the house over heats a lot and at times their is no heat call and the stoker stops running and the fire goes out after 5 minutes as the stoker is a flat bed stoker that does not hold the fire unless the hold fire timer turns on to keep the fire going. I have a B+G McDonnell & Miller RB122-E low water cut off as the first wired boile rcontrol.

And with a long spell of warm weather the fire goes out and that is another issue.

My thinking is either I use a large salvaged and tested hot water radiator steel piping and very small circulator or a Zurn garage heater hung up in the ceiling or with wall mount hanger.
The boiler vessel is 34 gallons in volume and the heating loop volume is very small being 225 foot of 3/4" copper fin tube baseboard and 20 gallons+-with the 10 gallons in the steel compression tank.

I do not want to use PEX tubing and I have ready access to steel pipe and unions. I just have to decide on whether I can get by with 3/4 black iron pipe, unions and ball valves to make the run to the heater or radiator.

The garage smallest garage heaters are 500+- with tax plus the cost of pipe and a circulator $100.00+- and a change in wiring adding a second run of BX from the new circulator to the single dump zone aquastat and wiring for the garage heater.
I am unsure if I can use the same single 12/3 BX leg for the dump zone circulator and the fan in the garage heater.


I want to keep it as simple as possible and I am thinking the second smaller circulator coming off the 3/4 tapping on the end of the boiler, feeding the radiator and then coming off the radiator returnto the boiler sump may be the best way to do this as the water will be very hot and the radiator will be large enough to shed the heat fairly quickly and return the cooler water to the boiler sump tapping that does not have the drain valve in it.

I would use isolation valves to valve off the circulator in any case to avoid water loss and a mess on the floor.

Thoughts and suggestions are welcome.


  • hot_rodhot_rod Member Posts: 12,894
    This is a common dump zone piping, both for dumping excessive energy and power outage, over-heat protection. Use large diameter fin tube, maybe a bit of upward pitch to encourage thermo siphon. This gives you some convection and radiant transfer. A small blower, even better.

    A small kick space heater could move some BTU, but the fan needs power so it would not work in power outages if that is a concern.

    I suppose you could calculate how many BTUs need to be dumped when your boiler has a belly full of energy and no load. Mainly you want to keep if from flashing to steam? So just dumping enough heat energy too stay below that condition?

    Ideally a dump tank so the energy is saved and can be used later.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • leonzleonz Member Posts: 329
    Hello Bob,

    Thanks for the screen shot. I have looked at the 490 gallon insulated tanks sold by the new horizon folks. It would be a huge heat sink that could be used to pull down the temperature in the steam chest. They run into some money at $1,400.00 plus tax and freight.
    If you have a schematic for a dump zone with a tank I would love to look at it.

  • hot_rodhot_rod Member Posts: 12,894
    Is it a steam boiler or hot water? You mentioned having 200'of BB connected to it.

    Do you want a dump zone that could work without a circulator being powered, in event of power outage? Or do you have a generator or backup power source so circulation is always possible?

    The same thermo-siphon would work if the tank were mounted above the boiler. Plenty of thermo-siphon solar thermal systems used around the world.

    Lots of wood burners use re-purposed LP tanks for buffer and or dump tanks. Find them is all sorts of sizes from 30 to 1000 gallon are common.

    I have a 500 gallon former LP tank connected to my wood fired boiler, previously had a 160 gallon. Used LP tanks go for about a buck a gallon around here.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • leonzleonz Member Posts: 329
    edited May 2019
    Hello and good morning Bob,

    I have hot water heat and 225 foot of 3/4 copper fin tube baseboard and it is the dump zone for the home.

    The system has to have power to work or the fire dies, I plan on changing the electrical feed so that I can use my generator to power it in the event of a power outage in the heating season.

    I have no room for a interior placed LP tank for a dump zone.

    My thought was to use a cast iron radiator parked in the laundry room along one wall where the stoker is located to dump heat.
    I found a place in Auburn, NY that has cast Iron salvaged hot water radiators and if I can find a big enough 3, 4 or 5 tube radiator I can plumb it in with steel pipe and it will be fine.

    I want add heat to the garage someday as all my heating is done with coal and it is very economical to use.

    I guess I should or could take the boiler drain off the top of the module, remove the reducer and add another short nipple and Tee to create the feed loop to the radiator and use a simple zone valve to divert the water to the radiator

    BUT I would be more worried about how well the zone valve would react to the higher temperature water versus using a very small circulator on the wall by the radiator with a check valve on the discharge side of the circulator mounted with shut off flanges to feed the hotter water to the radiator to dump heat.

    I would then reinstall the reducer and boiler drain to have the air vent once more for the pump module; I love that I do not have to crawl around on my knees to bleed the bloody things.

    Back to the dump zone:

    I will have the return come back to the steam chest in the right lower tapping to prevent boiler shock as the cooler water would then become heated evenly as the entire end wall of the boiler is wet with an average temperature of 150-180 degrees depending on heat calls or heat dumping.

    The near boiler piping is copper and I intend to change that to steel pipe.

    If I had good plumbing with 200+ feet of cast iron radiators which also heated the garage I would not need a dump zone but since I do not have them I have to add a dump zone.
  • hot_rodhot_rod Member Posts: 12,894
    I suppose it comes down to how often and how much you need "dump"?

    You could just fire up the circulator with a 210° aqua stat setting and just dump into the house baseboard. True, it will overshoot the temperature setting on the wall thermostat, but you already have the heat emitters, piping, etc in place. Just wire and addition control in series with the control on the circulator, when it sees dump condition temperatures it circulates.

    I'd rather you dump heat to a place you need or want it, the home, garage, etc. Typically not the boiler room :)

    Run the unit as efficiently as possible and avoid dump conditions, of course. I know that is easier said than done, being a solid fuel burner myself.

    Again, you could calculate the capacity of the boiler and determine how much you would ever need to dump. I suspect a 10- 20 minute run to dump from 210, or whatever temperature you decide, down to a safer 180, or ?

    I would not worry about the volume and mass of a single cast radiator, at boiler room temperature, shocking the boiler. It is a very small, quick load. One rule of thumb is 10%. If any load is less than 10% of the boiler output return temperature protection probably not needed. Snowmelt temperatures might be an exception

    The fin tube idea I presented for an additional dump emitter would be lower mass and water content, much better thermal conduction as copper heats up almost instantly. Plus it takes up less space if that is a concern.

    An adjustable electronic aqua stat would let you dial in the on/ off, differential to your needs, I use the Ranco or Johnson Controls brands for unlimited adjustability and digital readout.

    Pretty much all hydronic components have rated operating temperatures of 225°F pumps, zone valves, etc. Caleffi Z-one valves are rated to 240°F operating.

    Is the boiler pressurized? at 12 psi, you could run up to 244°F before flashing to steam, although that is not in my comfort zone. I think residential steam run ups around 215°
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • leonzleonz Member Posts: 329
    Hello Bob,

    When I wander over to Auburn I will check with the salvage people to see if they have any large fin tube that is in good condition too and go from there.

    I have a closed hydronic system with a 15 gallon steel compression tank-10 gallons of water-5 gallons of air ratio and the internal domestic coil is shut of as it leaks and floods the boiler-thank you keystoker (*&^%&*(.

    I am going to make a flow gate in the hopper by purchasing a piece of 2 inch strap steel to slow the flow of coal into the stoker this year and see how well that works along with controlling the stoker feed rate. I should have tried that in 2015 to begin with.

    I think by doing that it will be an easier to do as there is no restriction on coal flow on the flat 3 grate fire grate that is 8 inches wide and 13 inches long if I remember the dimensions correctly as it feeds a 2 inch thick bed of coal to the fire bed as the boiler runs the stoker.
    The three bed wide burner grate has 4 inches of solid grate then 7 inches of fire grate where the combustion air blows up through the bottom of the fire bed and it has 2+ inches of solid grate surface to let the burned coal ash up and than become clinker and then fall off the edge of the grates in to the ash pails.

    The hopper throat opening is 8 inches wide and 4 inches long and at anytime it is feeding 64 cubic inches of rice coal to the stokers pusher plate and the mass of rice or buckwheat coal also keeping the flue gasses in the firebox at the same time.

    I am sure that using a piece of 2 inch strap steel to cut the hopper flow into the throat of the stoker in half will be simpler.

    The way the system is set up the hopper continuously flows 64 cubic inches of coal into the stoker and the pusher plate speed of advance and retraction is regulated by a threaded rod that is adjusted to slow the feed rate or speed it up.

    The pusher plate is what delivers the rice coal to the flat burner grates creating a thick bed of coal that is slowed by a piece of 1" by 8" angle iron bolted to the stoker throat and frame.

    I use Honeywell mechanical controls; the L8124L1011 horizontal triple aquastat in Honeywell conductive paste; an L4006 aquastat or L6006 aquastat for the high limit control in the steam chest tapping without conductive paste.

    I also have a Mcdonnel &Miller RB-122-E direct contact immersion low water cut off sensor in place of the failed single hydrolevel 3250 plus and its dry bulb sensor that is also the triple aquastat bulb.
    Again thank you keystoker for nothing(*&^%$%^&*() as the hydrolevel 3250 plus controls failed on me twice-thank you keystoker again(*&^%^&*()_ .
    It pissed me off even more when I was running the replacement hydrolevel unit on oil and I was standing there watching it run and the computer in the bloody thing turned off the low water cut off function, again thank you keystoker(*&^%$#%^&*(.
    I had Honeywell mechanical controls in my old handfed wood and coal boiler and the old avco lycoming boiler before that and in 33 years they never gave me an issue let alone a wimper of a complaint.

    Onward to the fall heating season and if the strap iron solves the overheating issue by creating more control of the coal flow all the better and I will report back to you here Bob.

  • hot_rodhot_rod Member Posts: 12,894
    Certainly if you can limit the episodes of over-heating, a less elaborate dump system could be utilized. Spend the time, energy, and money on that first.

    100% stop on the the coal feed when the boiler reaches setpoint, close down or restrict air intake, and the output should drop off quickly. The compression tank itself may be enough of a buffer/ dump at that point.

    Wrap some aluminum flashing "fins" around the compression tank, install an inexpensive box fan at one end and you have a homemade, large capacity, already installed, forced convection dump radiator. If the tank is above the boiler it will thermosiphon if you have an in and out line, possible even in a single pipe, as two direction single pipe flow happens, and causes unwanted ghost heat transfer in some systems.

    It could be that simple.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • leonzleonz Member Posts: 329
    I have the B+G airtrol valve under the steel compression tank and It would be possible to extract more heat using a fan and some foil to try it anyway.

    The flat bed stoker has to run 12 minutes of every thirty as a rule to hold the fire since the fire will go out otherwise with less hold fire time.

    I may just remove the baffle in front of the flue breech for a while in the warmer months to see if that helps too.

    More to ponder.

    Thanks Bob

  • hot_rodhot_rod Member Posts: 12,894
    What is the BTU output of that coal beast?

    Sounds like you only have about 12,000 BTU of heat emitter connected? 225 feet of baseboard at 550 btu/ ft? And that load is only present on design days, probably less than 10% of the heating season.

    It may be tough to get the boiler and fin tube together on the same page. This is why buffer tanks are so commonly paired with boilers like yours.

    You compound the problem with a minimum 12 minute run cycle per hour?

    Also adding a dump may increase coal consumption, as the boiler "sees" this as an additional high temperature load.

    Either give it more work to do, or trying find a way to idle, without losing the fire. Most wood boilers idle by choking air, although that leads to inefficient, smokey burn conditions, not ideal but the lesser off two problems. Over-heat and pop relief valve, or smoke up the neighborhood :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • leonzleonz Member Posts: 329
    edited September 2019
    Hello Bob,

    I am coming back to the forum late and I saw your post.
    The boiler is gross rated for 120,000 BTU per hour on coal, oil and natural gas. I do not use kerosene anymore as its too expensive to buy and I am saving more money using coal.

    The domestic hot water coil failed last year and it was only three years old and I am using my small propane fired water heater for making hot water. I the domestic hot water coil was a trombone type domestic hot water coil I know it would have lasted much longer than the wound coil that is in the boiler now.

    I was told by the people I bought this thing from that I did not need a buffer tank but having a large buffer tank would prevent my having outfires and a cold house when it really gets bad up here on my mountain.
    I got a lot of bad advice and a bad very costly install plus the cost of the trouble calls to go along with that.
    The 2 sets of bad hydrolevel controls and junk mainland chinese made gauges caused a lot of problems and the dealer and keystoker were of no help to me whatsoever and I do not recommend the boiler reseller or these boilers or the plumbers I hired to anyone.

    If I had a pot stoker or a traveling grate stoker I would not have the issues with a poor burn or a cold house at times. I would have been able to leave the beautiful Buderus Logana G204 boiler in place and not ripped it out to fit the keystoker coal stoker I bought.

    If I could afford to rip out the baseboard heat and install cast iron radiators I would have plenty of thermal mass and no need for a buffer tank and no more outfires and I would be able to keep the boiler running at 170 degrees high limit even in the warmer months.

    The hold fire runs for 12 minute in total every half hour, 24 minutes every hour if there is no heat call. I can always add more pins to the timer to increase the burn time.

    I have to have a long hold fire time on this keystoker boiler as it is a flat grate stoker and will not hold a fire for very long without a hold fire burning or in a power outage.
    I only need a hold fire when the thermostat is not calling for heat.

    An EFM DF520 pot stoker or the traveling grate stokers made by the Axeman Anderson family or Alternate Heating Systems (axeman Anderson copies minus the open coal feed auger are different in that in the EFM burn pot stokers or the traveling grate stokers they have a very large mass of coal that is burning or idling and they do not require a very long hold fire time to keep the fire lit if there is no heat call and can still have a fire during power outages.

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