Wood Boiler BTU's Compared to Coal Boiler BTU's

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Post Sun. Feb. 21, 2010 2:58 am

Bought my house 4 months ago. Way to big for me and my girl. ( What can I say, we like room to breath) my old rental house, good sized cape cod,2000Sq. ft. gas bill 275 a month budget billing (nw pa.) new house still nw pa, smaller cape cod with 39 x 39 addition built on the back of it, 2700 sq ft. addition is bigger than the house. First bill $38.00, partial bill from buying the place ( still warm weather) and most everything shut down to minimum. Second bill was an estimate, only thing to estimate on was $38.00 previous bill. Expected shoot myself in the head gas bill. Started researching coal, expected 500-600 gas bills. Finally got bill, $596, it was for up to Feb.8 and the adjustment for Jan., about 320 per month. Cheapest coal I have found here is around 235 a ton. I do not own a truck. So more for delivery or a rental. Had to start thinking again. Like what I read about coal except for the short pre fab chimney life expectancy. Do not know if I should go with coal, Have a wood burner in the basement. There is a water jacket that goes from one side over the top to the other side, tied into the gas baseboard hot water heat. I would venture a guess at about 40 gallon capacity or near there. Huge fire box. Never had the chance to fire it up. Unknown to me there was an ice dam on the section of house that joined the old cape cod (bad for ice dams, chimney through the knee wall) to the new addition, Giant ice boulder dropped and took out a horizontal section of chimney. Will remedy or keep that under control from now on. So I read that pre fab cimneys do not last with coal (acidity problem) but, I also read that wood fires are not hot enough to support hot water baseboard heat. If I would go with the wood burner I would cut vents in the bedroom floor for heat and also in the entryway to the side of the house. Both are above the area where the woodburner is. The bedroom being directly above the woodburner. Well, I've never used either before so any info will be useful, what do you all think?

franco b
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Post Mon. Feb. 22, 2010 3:24 pm

Wood can provide as much heat as any other fuel as long as there is enough room in the firebox to hold enough wood. The trouble with wood is that when heated it releases a large amount of gasses which account for half the heat value of the wood, the charcoal that is left provides the other half. It is difficult to provide enough heat absorbing surface to absorb the heat of that rapidly burning gas without driving up the stack temperature and losing the heat up the chimney. When an attempt is made to burn slower by restricting the air to the fire it smokes and creates creosote. Some modern stoves have addressed this problem and improvement has been made to a degree. The best way to burn wood is to give enough air to burn fairly clean and feed it every couple of hours.

Hard coal on the other hand is 80 percent carbon so the gas problem is far less. Limiting the air does not cause smoke but does increase carbon monoxide in the flue gas which since it can burn if enough air is supplied is wasted potential heat. Long burn times can be expected. Usually tend every 12 hours. Though coal has about twice the heat per pound it will produce 10 to 15 percent ash as opposed to woods 2 percent. Coal stoves are more efficient owing to their lower stack temperature.

If your installation were mine I would fire it up with wood and try it out. First however I would advise you to have someone with expertise look over the installation for proper safety controls. A steam explosion can be very very violent. If it works well and is well made perhaps it could be retrofitted to coal.

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Rob R.
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Post Mon. Feb. 22, 2010 4:25 pm

A wood boiler can provide plenty of heat for hot water baseboard, but the problem is creosote formation and burn times. If you burn it hot to avoid creosote formation, the burn times are short. If you throttle it down to get long burn times, it will load up with creosote. If your firewood is properly seasoned, the creosote is easier to manage but still a problem.

I have a good-size wood/coal combination hand-fed boiler. I burned a few face cords of DRY firewood in it, and quickly decided I would save the remaining firewood for starting coal fires. Even with dry firewood, when nothing was calling for heat the smoke was terrible.

If you do decide to burn wood, I would not cut vents in the floor above the boiler. In the event any wood smoke rolls out the door of the boiler, your girl is not going to be impressed with the smoke coming up through the vents.

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Post Tue. Feb. 23, 2010 8:12 pm

I know I will get hell for saying this but..... it is probably going to be cheaper for you to stick with natural gas. Right now even though gas prices have gone up it is still cheaper for you to use natural gas at 235/ton for coal. If you use the fuel calculator and put in $9.50 per thousand cubic feet which is about what you should be paying and the 235 for coal you will come out on top with gas.

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Post Tue. Mar. 30, 2010 1:41 pm

A thousand cubic feet of gas equals a Therm, correct?
Do you think $9.50 a Therm is high?
In Wisconsin NG is about $1.27 a Therm.

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Post Tue. Mar. 30, 2010 3:26 pm

1000 cubic feet of gas would equal 1 decatherm or 10 therms, so 100 cubic feet = 1 therm.
The $9.50 seems like that would be the price for 1 decatherm.

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Post Wed. May. 26, 2010 2:04 am

Alright now you are starting to confuse me, Therm what, Yeah I know, I'm A freakin idiot. Not so much the cost savings, but want to buy all or most of the fuel ahead of time and have the power outage backup available. Have my generator in place, so no big deal on running the circulator for the water. Also worried about N.G. going through the roof again. If natural gas remains an option, no problem with me, though extra heat on mild nights would be nice.

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coal berner
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Post Wed. May. 26, 2010 9:14 am

NG gas would have to be 1.00 a therm to = 1 ton of coal at 230.00 a ton .
NG gas would have to be 1.05 per therm to = 1 ton of coal at 240.00 a ton . 100.000 BTU / Per Therm At 85% Efficiency
Coal 13.100 BTU per lb at 75% efficiency

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Richard S.
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Post Wed. May. 26, 2010 2:11 pm

You can do a reverse a calculation with the fuel comparison calculator.

Under the cost per unit column put the amount you expect to pay per ton for coal, do the same for natural gas. If you hit submit at this point all the way to the right it will give you a comparison based on costs per million BTU.

Once you have entered the values in the first section you can get estimates based on your current bill. From the drop down menu select natural gas and again be sure you are using the right unit type. The dollar amount can be anything, for example if you used $595 worth of gas you can use that. When you hit submit it will calculate what it will cost for the other fuels for the same heat.

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