Sizing Run Small Stove Maxed Out or Large Stove Idling???

Looking at getting my first whole home coal heater. Currently I have a old parlor stove heating my garage. Debating between a 96,000BTU unit and a 130,000BTU unit. Both hand fired. Thinking about the DS Machines new Circulator #4 or Circulator 96,000BTU. Is it better to get the smaller and run it maxed most of the time or get the larger stove and idle it for a majority of the time? Also would their be a difference of coal consumption for the same heat output between the two units? Want to be able to heat my house easily but do not want to hurt my stove or waste coal. Is going to big a bad thing? Any advice would be greatly appreciated. Thanks.
RSCK

rsck wrote:Looking at getting my first whole home coal heater. Currently I have a old parlor stove heating my garage. Debating between a 96,000BTU unit and a 130,000BTU unit. Both hand fired. Thinking about the DS Machines new Circulator #4 or Circulator 96,000BTU. Is it better to get the smaller and run it maxed most of the time or get the larger stove and idle it for a majority of the time? Also would their be a difference of coal consumption for the same heat output between the two units? Want to be able to heat my house easily but do not want to hurt my stove or waste coal. Is going to big a bad thing? Any advice would be greatly appreciated. Thanks.
RSCK

The first thing I think you should look at is how many BTUs do you currently require to heat your house comfortably. If the area you are looking to heat only requires 80,000 BTUs then the smaller unit will work with BTUs to spare so why put out the additional money for the larger stove. However, if the you need 95,000 BTUs on a normal day you may want to spend the additional money just for the piece of mind it will bring. Running a coal stove at max 24/7 shouldn't hurt it but it is very easy to slip into an over fire situation and cause damage to the stove. That's the risk of going with the smaller stove during a cold snap. I'm not familiar with the DS stoves but generally, running a stove at idle is a good thing. It maintains your heat but using little coal in the process. I would bet that the smaller unit running full out would equal the BTUs of the bigger one at idle and use the same amount of coal. That makes your choice 6 of one, half a dozen of the other. If that were the case I'd say, go with the larger one unless cost is an issue. Just my thoughts, Lisa

Hi rsck and welcome to the forum. Here are a few calculations that you will find interesting. I hope this helps you to be able to decide.

Re: BTU output question

PostBy: DOUG On: Fri Feb 19, 2010 9:37 pm
Here is a neat formula to use for obtaining a good idea of the BTU burning capability of a hand fired coal stove. Use the grate area, not the size of the firebox, fire pot, or fire brick.

GRATE AREA SQ.FT. x .65, THE PERCENTAGE OF EFFICIENCY x 8, THE POUNDS OF ANTHRACITE PER SQ.FT. x 12,500, THE AVERAGE BTU's PER POUND OF ANTHRACITE.

Here is a calculation for you that will interest you. I showed this to Larry Trainer, the designer and manufacture of the Coal Stove Chubby, and he was amazed that it was so close to the actual laboratory test results. I got it from a book Solid-Fuel Furnaces and Boilers, by John W. Bartok, copyright 1982.

Grate Area (sq.ft.) X percentage of combustion efficiency X pounds per sq.ft. on grate X BTU output of fuel

The large Chubby has a grate area about 12" round. To get the sq.ft. of grate area, we take 12/2= 6, 6X6=36, 36X3.14=113.04 Sq.in, 113.04/12=9.42, 9.42/12=.785 sq.ft.

The percentage of combustion efficiency for most coal stoves is 65%, unless stated otherwise, 50% most wood stoves unless stated otherwise, the Chubby states between 85% to 90%.

The pounds of fuel per sq.ft. of grate per hour are: Anthracite Pea 5, Anthracite Nut 8, Hard Wood 20.

The Average heat output of fuel is: 12,500 BTU's for Anthracite and 6,500 BTU's for Wood.

Now that we have some definitions, lets do some calculations.

The large Chubby in the wide open damper, most heat up the chimney: .785 X .65 X 8 X 12,500 = 51,025 Btu's
The Large Chubby in the half open damper, .785 X .85 X 8 X 12,500 = 66,725 Btu's
The Large Chubby with the Damper mostly closed, .785 X .9 X 8 X 12,500 = 70,650 Btu's

So, Larry's figures are correct. This is a really neat formula that can be calculated for any stove. There are other numbers for different fuel types to run these calculations. The only thing is when trying to calculate other stoves, we can't assume just by closing the manual damper that the efficiency will go up. The efficiency ratings have been started to get published more by manufactures, especially now that the government tax credits for wood stoves have been instituted.

Okay, to answer the size question of the Jr. Chubby, it is 28" high with the legs, 14" round, 16" round on cast iron top, 23" to the top of the rear flue. I'm guessing that the weight is about 100Lbs. At least that is what it feels like to me.

Now let's run some numbers on the Jr. Chubby. The Jr. Chubby has a grate area around 8" round. That is .3489 sq.ft.

The Jr. Chubby in the wide open damper, most heat up the chimney: .3489 X .65 X 8 X 12,500 = 22,648.5 Btu's
The Jr. Chubby in the half open damper: .3489 X .85 X 8 X 12,500 = 29,656.5 Btu's
The Jr. Chubby with the Damper mostly closed: .3489 X .9 X 8 X 12,500 = 31,401 Btu's

There are other formulas to calculate the heat output of stoves too. Here is another one.

Re: Stove BTU output based on temp and surface area?

A chart from "The Wooburner's Encyclopedia,1976" says: The amount of heat emitted per square foot is dependent on the temperature of the radiating body.

Temperature of Surface Fairenhiet -------------- Total Energy Transferred BTU's per hour per foot

80* ------------------------------------------------------ 15 BTU's / Sq.Ft.
100* ------------------------------------------------------ 51 BTU's / Sq.Ft.
150* ------------------------------------------------------ 168 BTU's / Sq.Ft.
200* ------------------------------------------------------ 315 BTU's / Sq.Ft.
400* ------------------------------------------------------ 1230 BTU's / Sq.Ft.
600* ------------------------------------------------------ 2850 BTU's / Sq.Ft.
800* ------------------------------------------------------ 5430 BTU's / Sq.Ft.
1200* ----------------------------------------------------- 9370 BTU's / Sq.Ft.

This formula will get us close and usually assumes 50% to 65% efficiency stoves though. Here is an example for the Jr. Chubby:

The Circumference of a 14" round pipe is 43.98" X the height of the stove body, minus the legs, is 23" X the area of the 16" round cast iron top 201.06", then multiply the total in sq.ft. by the outside temperature of the stove.

So, 43.98 X 23 = 1011.54 + 201.06 = 1212.6"/12/12= 8.42 sq.ft. X let's say 600 degrees F 2850 BTU's = 23,999.37 Btu's

That's pretty close. Neat, huh?

Hi DOUG, can you tell us why the Chubby stove has a percentage of combustion efficiency so high 85 to 90% ? Have you some numbers about the Glenwood Base B. efficiency? Thanks for the info you gave on your last post. It is very instructive.
Salutations, nortcan

The choice is in this case not between small and big but big or bigger...
Check the heat loss of the garage with a caculator...
Then check how big a heater, BTU wise, you have now...
The difference between the stoves is 30% or so...
If the heat load is very close to the 96,000 BTU then you need to go larger...
If you want to keep the building at a normal temp on an abnormally cold night.
I have the Basement #4...
It holds 175 lbs of coal with the hopper loaded...
Do get the hopper, I will never buy a hand fed without one...
Heating 1900 sq ft to 74* no wall insulation, on The Cape...
High heat load when the wind and cold combine...
The stove runs about 450* during a normal winter night...
The stove is running at about 70% of its rated output...
Have yet to need the last 30% but it was a warm winter here...
At this setting getting 12 hour burns are no problem...
For a garage I would go with the bigger stove...
How big is this garage, how high are the ceilings, how well insulated is it and how often will the doors be opened...
I can drop the stove to 180* in the early spring and late fall and not overheat the house...
Early fall and late spring is a bit trickier...
I let the stove ash up and cut the coal bed by half...
I use Pea coal during this time for better low temp control...
I am building a firebox reducer so I can burn the Pea coal without playing the ashup game...

Hi nortcan, I'm not sure why the Chubby is so efficient. Here is a write up from a book called "Coal Comfort" by Peter Hotton, this is what it says. As for the Glenwood Base Burner, I haven't seen an official write up yet.

Hi RSCK,
I have the 130k circulator, let me just say that DS Machine rocks. Also like cape coaler said make sure you get the model with the hopper it makes everything easier. This was my first time with a hopper and I will never have a stove with out one again. Are you going to be putting the stove in your garage or in a basement. tell us a little about your house size, insulation, type of temps common for your area ect. Personally I would get the large one unless you have a small home. the coal consumption I would assume would be the same except at idle on your warmer days, stoves with larger btus outputs just have larger fireboxs thats all. The amount of coal burning is what gives your btus (my previous statements on coal consumption is for ds machine stoves I am sure people have smaller stoves that may heat better, and larger ones that do not heat as well.) However and I'm just pulling #'s here if you only need 5kbtu and the large stove can only go down to 8kbtu at idle on a warm day then yes you would use a little more coal. I always liked having the capabilities to put out more if needed though. Just my two cents hope this helps
Have a great day, Eric

DOUG wrote:Hi nortcan, I'm not sure why the Chubby is so efficient. Here is a write up from a book called "Coal Comfort" by Peter Hotton, this is what it says.

DSCF2288.JPG

As for the Glenwood Base Burner, I haven't seen an official write up yet.

If you all are interested I will be happy to do a write up on the Glenwood with dimensions, drawings, photos, etc. I didn't want to bore people to death with my enthusiasm for the Base Burner, however; I have posted about it all over the place and it might be good if all the stuff was in a single thread so any one who wanted to could find it and ask questions. I think it would be neat if more people found out about how extraordinary these stoves are. Just let me know.

Oh, by the way; to answer the question here. First, you have to answer the question. In what capacity will I use my stove? If you are going to use it for a principal or sole source of heat then you need one with extra capacity. In my years of fooling with stoves I have found it to be easier to cut back a large stove than it is to push a smaller stove to provide more heat than it is really designed for. It is possible to push a smaller stove to a high capacity for short periods of time, but; it is very bad for it and could possible lead to overheating, damage to the stove or worse a house fire.

wsherrick wrote:If you all are interested I will be happy to do a write up on the Glenwood with dimensions, drawings, photos, etc. I didn't want to bore people to death with my enthusiasm for the Base Burner, however; I have posted about it all over the place and it might be good if all the stuff was in a single thread so any one who wanted to could find it and ask questions. I think it would be neat if more people found out about how extraordinary these stoves are. Just let me know.

Would like very much to read your revue of your stove, especially with pictures of the damper arrangement to accomplish base burning, plus firebox and grates.

Yes, I second that. Please put a thread together for the Glenwood Base Burner. Thanks.

My house size is approx 2500 square feet, 1250 each level. Garage is approx 700 square feet. Current wood furnace is rated 120,000 btu. Do not really idle it much. Burn around 3.5 - 4 cord of hard wood. Just heating my home. Plus coal for the garage. Have forced air ducts plus returns all through my house even the garage. Was thinking if putting coal stove in garage. Right now I have ducts shut off to garage. House is well insulated. Nothing to have several weeks of -20F - -30F at a time. Very rare to have to many days in a row of -40F or -50F. Couple days during the winter only. Sometimes we get weeks of just below freezing. Garage is used as a work shop. Only open garage door to get snow blower out. So not open very often. Only open long enough to get blower out.

IMHO you would be best off with the larger one. There are ways to make a big stove run efficently at low output but there is no way to get max efficency out of a stove while getting max heat.

Bruce

rsck, Where do you get your anthracite in New Brunswick?

Tamecrow wrote:rsck, Where do you get your anthracite in New Brunswick?

Hi Tamecrow
I get my coal from either Houlton Maine or Easton Maine. Approx 100 miles away. Their is no anthracite currently harvested in Canada at this time? You burn Bituminous coal there in NS? If you burn Anthracite coal where do you get it? Even the travel included still cheaper than wood, oil, or electric.