need more heat

That is as fast as it burns, meaning volume goes away, about 3-4 bags at 50# each per day. I might be able to get it to burn air adding a blower to the air intake. I am trying it piled up pretty high today and seeing what happens. Still in the 130's as of now. We will see. If it isn't up by 9 or so I will add fan and see if I can burn it faster. Again all input is appreciated. I will stick a high end thermometer and check the flue gas temp.

Time to take bets! I'm putting my money on coaledsweat's fan-forced draft idea. My brother has an outdoor boiler, and the chimney is not tall enough to create much draft on its own, which would explain why you can put "only" 150-200 pounds of coal per day through such a big unit. Like I said, compared to my stove you have eight times or more the cubic volume of burning coal but you are able to vaporize only 3 to 4 times the quantity per day. And I'm not even pushing mine!

Also, what size coal are you burning? I have read that stove coal (larger chunks) will burn hotter and faster than nut coal, because the air can pass through quicker. But I don't know if you need a bed deeper than 10 inches to burn the larger size.

Beg, borrow or steal a leaf blower. Fire it up and put it to your draft intake. You will know in 10 or 15 minutes if your on to it. If things start turning a light orange........ back off.

Do you think mixing coal and wood would work.

I have an outdoor wood burner and I was thinking of getting some Nut or Stove and throwing it on top of the wood to longer burn times. Headed town tomorrow to look at a new coal boiler. Maybe a summer project for me.

One of my brothers got some bituminous coal and added it to the wood fire. Family dinner was interrupted by an explosion that blew the door off the stove and filled the house with yucky smoke. So perhaps it's not a good idea to mix coal in with wood in a unit that's not designed to burn it.

(Note on the proper comportment of wives: I heard this story from the man himself, years later. His wife never told on him.)

rberq wrote:Time to take bets! I'm putting my money on coaledsweat's fan-forced draft idea. My brother has an outdoor boiler, and the chimney is not tall enough to create much draft on its own, which would explain why you can put "only" 150-200 pounds of coal per day through such a big unit. Like I said, compared to my stove you have eight times or more the cubic volume of burning coal but you are able to vaporize only 3 to 4 times the quantity per day. And I'm not even pushing mine!

Also, what size coal are you burning? I have read that stove coal (larger chunks) will burn hotter and faster than nut coal, because the air can pass through quicker. But I don't know if you need a bed deeper than 10 inches to burn the larger size.

I am burning stove coal. I added a fan to the intake, just a small window fan and I might be burning a little more coal faster, but temperature is still not there. I might try the leaf blower idea tomorrow because i will be at the house to watch it. If i add to much coal it drops the temp drastically for several hours before coming back up to a peak still in the 120's

I don't know if this has been ascertained or not ... What are you trying to heat with this "outdoor forge"?

Here's a thought, but I'm not sure if this is the case as I haven't seen the drawings on this one so I'm not sure how its set up.

The thing that bugs me about these outdoor heaters/furnaces is the huge water volume, I just don't understand the need for that kind of capacity. It also may be the problem here, 200 gallons is huge. If your firebox is considerably shorter than the jacket, the returning cooler water may be going by the fire at the front and rear of the boiler and bring the temperature down on the water you do heat as it blends prior to the outlet.

Does that make sense?

I don't think it will ever burn coal well, mostly due to the design of the unit. From the diagram it doesn't look like it would lend itself well to coal burning. Also, it consumes large amounts of wood, wouldn't it use lots of coal if you get it to work? I think a conventional coal fired boiler in the cellar would function better and save enough on coal costs to pay for itself in short order.

Dallas wrote:I don't know if this has been ascertained or not ... What are you trying to heat with this "outdoor forge"?

I am heating a brick house built in 1862 about 4000 sq ft and we have radiators. The sytem works fine, the circulation is good, I have been using this for 8 years with wood. I am just trying coal to save my back and the prep time of cutting and splitting wood. The first winter I was here I used oil and went through 2800 gallons of fuel oil. I have made some changes to the sytem and gotten rid of some pretty bad air loss problems. I used 20 -25 cord each year since. love the outdoor furnace vs indoor because of the fact of I am not blowing all that air out of my house through the chimney and sucking in huge quantities of air as combustion air. No drafts and the house is much warmer since we stopped having the "fire" in the house. I am convinced that the only problem is that I am not able to burn enough coal to get enough BTU's for that amount of water. The coal fire burns steady and creates a wonderful hot bed of coals, but it is just not going away fast enough. I need to burn mor like 400# a day? What is the calculation for BTU per gallon of fuel oil?

Fuel oil is approximately 140,000 BTU per gallon. A good boiler will deliver maybe 85% to the house (don't quote me on that, I'm no pro). So 119,000 BTU per gallon. So 2800 gallons in a year is 333 million BTU.

Anthracite coal number I have read are 22 MBTU to 25 MBTU per ton. Call it 22 to be conservative, and 70% efficiency in your setup, so 15 or 16 MBTU delivered per ton burned.

25 cords of GOOD wood (i.e. dense wood) might be 62,000 pounds, 8000 BTU per pound gives maybe 500 million BTU, but adjust that by the same 70% efficiency and you have 350 MBTU per year delivered from your 25 cords.

So far, so good, because the above oil vs. wood numbers crossfoot pretty well -- 333 MBTU from oil, 350 MBTU from wood. Also your fuel oil use was comparably in the same ratio as mine for my smaller same-vintage house, which is another good cross-check.

So now for the payoff. We'll say you need 350 MBTU per year, and coal will deliver 16 MBTU per ton, so you need to burn 22 tons of coal over the course of your heating season. So divide 44,000 pounds by the number of days in the heating season, and that is the AVERAGE pounds per day you have to burn. Multiply that by perhaps 1.5 because you will need more heat on colder days, so your system should be sized for that. So if your heating season is 150 days, the calculation is 44,000 pounds divided by 150 days, times 1.5 for the colder days, and TA DA you will have to burn 440 pounds per day on a cold day, much less on warm days.

WHEW!

Number 2 oil is 138,000 BTUs per gallon and would equate to about 10 lbs. of anthracite coal. That would be about 14 tons of coal for the same heat, I would add two or 3 tons as the efficiency is lower on the coal boiler. That is about $9,000 for oil and 18 tons would cost about $4500 worst case. These numbers appear to match well with the cordwood numbers used that you have given us.

If you were burning 20 gallons of #2 a day, you will need to burn about 230# of coal a day for the coal to match its output. This is about 50+ # less than what you are burning. You need to force a draft, the coal is going to need a lot of air to feed 250# a day.

Another thing would be your oil unit is inside and does not have the losses to the cold that your outdoor unit has. That may add another 30# or so of consumption per day, I just don't know.

You've had the fire going well long enough so we know that works, now it has to go to work for you. The strawboss may be the blower. I don't know what you have for a stack, most of these outside things only have a foot or two. Twenty feet of stovepipe might liven it up too. Without it, you basically have no draft and anthracite needs it or it will be lazy.

Don't forget the efficiency of the outdoor boiler. I would bet its less than 60%.

cArNaGe wrote:Don't forget the efficiency of the outdoor boiler. I would bet its less than 60%.

One article I read said 43% avg efficiency on an outdoor wood boiler http://www.oag.state.ny.us/press/2005/a ... 202005.pdf

At lower efficiencies, maybe a lot more than 440 pounds per day. You will need your own railroad siding.