Coalpail.com Forum

hello everybody I have a quick question on what would get me better efficiency on my coal boiler making dhw. I have a keystoker kaa-2 and I am running in series with my oil burner. the way I making my hot water is using a boiler mate that is taking boiler water from the keystoker and circulating it through the boiler mate to generate my hot water. I also have an instant hot water coil installed on the keystoker that is not being used. I was wondering what would get me better Efficiency and less coal usage? the curent set-up with the boiler mate or to hook up the hot water coil. right now I have a family of 5 using the dhw and ai buring around 15# a day I have my aquastat set at 120-140. I was hoping to get down to 8-10# a day.

I don't think you will do better than what you are doing right now.. The big advantage your current setup has is that it stores hot water... Coal is slow to respond to a call for heat.. so if you had someone taking a shower, and ran the dishwasher or a load of laundry at the same time,,, you would probably drop the 140* water to about 110-120* and have to wait for the coal fire to catch up and heat the water up to an effective level for heat transfer to the coil in the boiler.

With the stored water,, you have a buffer, allowing the use of stored hot water while the boiler is increasing the coal fire to make up for the water use.

AND... to save an extra 5# of coal a day,, times 30 days a month, equals 150 # of coal.. only a few dollars , even at bagged coal prices, only about $20... you can save much more money in your monthly budget by carefully planning your errands, and carpooling for errands and commuting to work... I just spent $50, YES $50 to put half a tank of gasoline in my junk minivan !!. It costs me $20 in diesel just to mow the yard...

Anyway sorry for the 'rant'.. I think you are doing VERY WELL on coal use to make hot water for your family..

Greg L

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I agree with Greg, if you have five people using hot water and using 15 pounds a day.... life is good!

Perhaps you could save some coal though, if you shut it off during the week, used paper plates, and fired up the boiler on Saturday morning. You could wash the silverware, do the laundry and everyone take a weekly bath.

Well if we are going to be silly Freddy - let me play too!

You could be more efficient if you charged 180-200 degrees of stored energy into a well insulated 1000 gallon propane tank with your boiler. Heat it from the top down and draw energy (hot water to exchange into DHW water) from the bottom up!

In building this energy store, you could run your boiler at full tilt - at max indecency - and then shut it down for the week - until you needed to repeat the cycle. The down side being the extra thermal cycles and cold starts on your coal boiler will decrease appliance life - but if fuel saving is you goal - there ya go -

Now add some solar energy collection into your new thermal energy storage tank with roof panels and maybe you can park the boiler for a longer period - reduce its start stop cycles - and burn NO coal

I agree with Sting, except for one major difference.. my suggestion, or Freddies suggestion doesn't require 1975GT to spend any money to save money.. But Sting's plan, while a viable idea, would cost hundreds, actually probably thousand ++ to setup, plumb and lear to make work correctly..

I actually like the idea of paper plates, and once a week showers.. makes the kids appreciate what they have now.. and what it costs to live well..

I grew up counting pennies and nickels, had to, my parents kept taking in foster kids.. my temporary brothers and sisters... we had too many mouths to feed and laundry, and hot water.... I remember standing in line so I wouldn't loose my place for the bathroom.. , almost had to water the houseplants some mornings !!

Greg L

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Your right AGAIN Greg

But that wasn't a parameter of the question: What will give me better Efficiency? "i was hoping to get down to 8-10# a day."

Ask me a question like that and expect and answer Run the boiler at full tilt rather than limp it along at idle fire - best bang per pound of fuel - store the excess energy for a rainy day rather than scrub it off in a heat dump. Or use solar for summer DHW production and save more coal.

I am guilty again of forgetting fuel is still cheep for my friends from the East! And I am thinking too long term!

Oh I agree, Sting.. but I do question an insulated hot water storage tank,, it would have to be a vent to atmosphere and gravity feed, or a separate pumping system from the house supply water,, otherwise how would you get the hot water through the house system without having cold supply water diluting the hot water??

And another question: what is the heat loss of a water tank?? you have to store a lot of hot water,, at just below boiling, so the delta-T* will be high to the ambient. The actual amount of heat going up a chimney from an idling coal stoker is very low.. even my AA260 [pretty big idling fire] has flue temps in the low 100's when idling.. I'd bet the flue temps from the Kaa2 are pretty low..

The efficiency of the coal boiler,, I'm not real sure it is higher when the stoker is cranking out the max... Unlike wood, that needs to burn really hot to burn completely,, a coal fire burns completely and at nearly the same efficiency with a small fire or a huge one.. The greater efficiency would be from a higher delta T* between the firebox temps and the water temp. ???? I think this is right..

Anyway,, this discussion went from serious, to having fun, back to semi-serious..

For the extra 5# of coal burned per day,, if not bagged at $300/ton, but rather bulk at roughly $150/ton, then the difference is only about $10.. A Dunkin Donuts donut and a fancy coffee.

Greg L

hey thanks for all the help and I like the joking around maybe I will hold back on the wifes precriptions meds for extra coal money. I am curious about what sting has said about running the coal boiler at full tilt or just let it idle along. right now it just idles along all day until nite time when we take showers during the maint fire my flue temp is about 100-110 degrees on a stoking fire the stack temp will hit 300 degrees. I havent changed anything with the stoker feed but did adjust my aquastat down to 120-140 from 160-180 and the othe change was I pulled a bunch of pins from my timmer now it runs 30 seconds every 10 minutes downd from 1 minute 30 seconds every 10 minutes. would I use less if I ramped up my fire quicker or what. I was going to give keystoker a call and see what they say for optium performance. you would think they would have tested these boilers to see what the max they can get out of them.

I would say that a call to keystoker is a good idea.. but it sounds like you have it set pretty near perfect.. how much fire is there on the grate when you get home?? Before any hot water is used?? If you have only abut an inch of fire, the full width of the grate and no unburnt coal on the sides of the grate [this is where the fire starts to go out, against the side walls of the grate], then I think you can't 'wean' the fire anymore than you have.. With only ~100-110* flue temps, it sounds like you have a pretty small idle fire..

Whatevery you do, don't withhold prescription drugs from your wife!! You never know the consequenses !!

Greg L

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i only have about an inch of fire going across my grate but the only thing I noticed sinced I shrunk the maint fire down is the increase of stoker time. it seems to take a while for the fire to ramp up because it takes a while to get the coal to the air holes in the grate. right now my fire is about 2 inches off the stoker about an inch of fire and about 8 inches of ash. I was wondering if I move the maint fire closer to the air holes it shoud ramp up faster and in theroy it should use less coal. I always asked the question and never got a clear answer. is it better to stoke longer at a low fire or the stoke shoter with a bigger fire?

A bigger fire will ramp up quicker,, but no matter what, a bigger fire will burn more coal.. If you have too much lag with the stoker's fire,, you may want to manually stoke up the fire about 20 minutes before the high use of water starts.. I'm not sure with your stoker design if it is an easy thing or difficult to jsut get the stoker to push an extra inch or so of coal onto the grate.. With the LL stoker stoves,, you can manually opperate the coal pusher, and this is the only hands-on experience I have with bed-type stokers.

Greg L

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ther is no manual stoker feed on my keystoker but I would be nothing wire a button on the boiler or even one up staires. just push the button to feed the coal and then have dinner then be ready for showers. it may work . in your opion how long do you think the boiler should stoke for to come up to temp. right now the boiler hangs around 150 all day when the boiler mate calles for heat it can drop down to about 130 and then stoke for about 45-60 minutesto get back to temp but then after the boiler mate stopes teh call for heat the boiler will shoot up to 180-200 and that is wasted heat. any suggestions gregg

1975gt750 wrote:hey thanks for all the help and I like the joking around maybe I will hold back on the wifes precriptions meds for extra coal money. I am curious about what sting has said about running the coal boiler at full tilt or just let it idle along. right now it just idles along all day until nite time when we take showers during the maint fire my flue temp is about 100-110 degrees on a stoking fire the stack temp will hit 300 degrees. I havent changed anything with the stoker feed but did adjust my aquastat down to 120-140 from 160-180 and the othe change was I pulled a bunch of pins from my timmer now it runs 30 seconds every 10 minutes downd from 1 minute 30 seconds every 10 minutes. would I use less if I ramped up my fire quicker or what. I was going to give keystoker a call and see what they say for optium performance. you would think they would have tested these boilers to see what the max they can get out of them.

Again I will stand in anguish to driving a boiler especially at idle fire below 140 on the vessel temperature. I would suggest you look very carefully at what may (or may not - every machine is different) be condensing and building on fire chamber walls - HX tubes and insides of smoke pipe.

Now to the (my opinion) about running a boiler at full tilt vs idle fire --- idle fires are a waste of fuel period. UNLESS you can tweek that idle fire so low that the outside of the vessel is ambient room temp. (because its insulated that well) and you are carrying 140 degree water inside the vessel to keep products of combustion from condensing on all the paths of exit. The fire that ramps up to full burn is also a waste of fuel - its simply heating the contraption to get to best possible exchange temperatures.

Burning at capacity is what the machine was designed to do - everything should be tuned to that goal.

Now what do we do with all that energy - we use it or we store it and use it later when we are back on idle fire - (so we don't have to build a fire box again) or we shut down for the week and live off the storage.

1000 gallons of well insulated tank stored energy can supply a moderate household DHW needs for many days - its all about demand from there and how you charge and draw off that stored energy. That stored energy under pressure in the 1000 gal INSULATED tank is no differant than the energy stored in that much smaller appliance vessel under idle fire - but yes it does require a significantly larger expansion tank to host a system like this. A 50 gallon electric water heater is economical expansion tank when modified slightly. But energy exchanged from storage is no different than energy created at the moment and exchanged from the appliance. It all a matter of control.

Once you have storage - you will wonder how you burned coal in the summer - but when you back in the "season" you most likely will valve the storage loop off the system and run as always. To make that algorithm pay - you need to consider the solar option to recharge the stored energy tank as often as there are sunny days - keeping in mind when that falls behind - and undersizing solar grids is not a bad thing - you may need to fire the boiler and recharge ocasionally.

But thats just my crazy systems - your mileage may vary - You may not have the "heart" to tend such a system - and why should I blame you can get jump in the truck and go get 50 pounds out of the ditch when ever you need it!

ok serious to joking - its all fun! Many say I am off my meds most days

just thought I could lower my 4006b aquastat to dump the exrta heat into the hotwater tank because that is my dump zone.
and that boiler mate is well insulated and would keep in the heat rather than going up the chimney
just a thought

Sting,, remember, there is nothing to condense from a coal fire,, there is just some fly ash. and heat.. I have run my boilers as low as 120*, and a brush will wipe off the fly ash.

Now, an LP, NG, Pellet, or cornburner or wood burner,, they create water in the combustion process.. a whole 'nuther story.

Greg L