Stove Efficiency Vs. Size Question

 
User avatar
lsayre
Member
Posts: 21781
Joined: Wed. Nov. 23, 2005 9:17 pm
Location: Ohio
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Lehigh Anthracite Pea
Other Heating: Resistance Boiler (13.5 KW), ComfortMax 75

Post by lsayre » Tue. Jan. 11, 2011 5:42 pm

Which is considered more efficient? A larger stove throttled back and running at a lower surface and stack temperature, or a smaller stove running with a higher surface and stack temperature, if both are putting the same relative number of BTU's into the house?


 
User avatar
Coalfire
Member
Posts: 1029
Joined: Mon. Nov. 23, 2009 8:28 pm
Location: Denver, PA
Hand Fed Coal Stove: DS Machine 96K btu Circulator
Coal Size/Type: Nut

Post by Coalfire » Tue. Jan. 11, 2011 5:48 pm

Bigger is better hands down. You can throttle them back. If still to much heat run pea coal. I belive if you crank a small stove to much you will not radiate the heat as fast. Just not enough surface area to do it effectivly, Like wise if you have a big stove and have to max it out you would also run into efficiency issues. So I guess the best bet is to know your house and buy an appropiate size. Cause on the flip side a larger stove still has to consume a certain amount of coal to idle.

 
franco b
Site Moderator
Posts: 11416
Joined: Wed. Nov. 05, 2008 5:11 pm
Location: Kent CT
Hand Fed Coal Stove: V ermont Castings 2310, Franco Belge 262
Baseburners & Antiques: Glenwood Modern Oak 114
Coal Size/Type: nut and pea

Post by franco b » Tue. Jan. 11, 2011 5:58 pm

I think the smaller stove will run more efficiently because it will have a hotter fire. I also think it is dependent on the particular stoves involved.

 
User avatar
lsayre
Member
Posts: 21781
Joined: Wed. Nov. 23, 2005 9:17 pm
Location: Ohio
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Lehigh Anthracite Pea
Other Heating: Resistance Boiler (13.5 KW), ComfortMax 75

Post by lsayre » Tue. Jan. 11, 2011 6:03 pm

Coalfire wrote:Bigger is better hands down. You can throttle them back. If still to much heat run pea coal. I belive if you crank a small stove to much you will not radiate the heat as fast. Just not enough surface area to do it effectivly, Like wise if you have a big stove and have to max it out you would also run into efficiency issues. So I guess the best bet is to know your house and buy an appropiate size. Cause on the flip side a larger stove still has to consume a certain amount of coal to idle.
I agree with the above, but better (and safer) may not equate directly to higher efficiency. Have any studies been done to measure the efficiency of a small and high temp. coal fire vs. a large and moderate temp coal fire?

 
User avatar
Cap
Member
Posts: 1603
Joined: Fri. Dec. 02, 2005 10:36 pm
Location: Lehigh Twp, PA
Hand Fed Coal Stove: Harman SF 250, domestic hot water loop, heat accumulator
Coal Size/Type: Nut and Stove
Other Heating: Heat Pumps

Post by Cap » Tue. Jan. 11, 2011 6:19 pm

If I burn at a simmer, my stack temps will be equal to or sometimes lower than the fanned hot air into my living area. If I burn hard, my stack temps will be higher than the warm air being pushed with the stove fan. This indicates to me that I will see better efficiency with my particular unit BUT this may NOT be true with all stoves. I know my stove has the benefit of an additional heat exchanger. I have a rather large hand fired unit.

 
User avatar
PC 12-47E
Member
Posts: 772
Joined: Tue. Nov. 25, 2008 11:45 am
Location: Mid Coast, Maine
Hand Fed Coal Stove: Estate Heatrola, Jotul 507

Post by PC 12-47E » Tue. Jan. 11, 2011 6:21 pm

Over the last three winters I have heated with large stoves (year one 120,000 BTU), (year two 105,000 BTU), and this year with 2 small stoves each rated at 45,000 BTU's. We are heating the same 3,000 SQ/FT drafty old house. Heating with the two small Jotul 507's in place of a single large stove our anthracite coal consumption is up by 50--100 lbs a week. :o Also this winter is not as cold....at the moment we are burning 450-500# a week. Also we do not have the same hi heat output as with the larger stoves......
All stoves vented in the same 8"x8" 37' tall chimney. Barometric damper set @ -.05 to-.06 WC.
Your coal mileage may vary. ;)

Year one, Harman SF-250 120,000 btu.

year two, Gibraltar DDI 105,000 btu.

year three, twin Jotul 507's 45,000 BTU each = 90,000 btu

PC 12

 
User avatar
lsayre
Member
Posts: 21781
Joined: Wed. Nov. 23, 2005 9:17 pm
Location: Ohio
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Lehigh Anthracite Pea
Other Heating: Resistance Boiler (13.5 KW), ComfortMax 75

Post by lsayre » Tue. Jan. 11, 2011 6:23 pm

Great info there! I'm chalking that up in the bigger is also more efficient category.


 
User avatar
VigIIPeaBurner
Member
Posts: 2579
Joined: Fri. Jan. 11, 2008 10:49 am
Location: Pequest River Valley, Warren Co NJ
Hot Air Coal Stoker Furnace: Keystoker Koker(down)
Hand Fed Coal Stove: Vermont Casting Vigilant II 2310
Other Heating: #2 Oil Furnace

Post by VigIIPeaBurner » Tue. Jan. 11, 2011 8:01 pm

IMHO, this question isn't one that can be accurately answered with anecdotal stove experiences. If 2 stoves, radiant or convection, are capable of consuming the same amount of identical coal hooked to cloned chimney/weather conditions, the one with more surface area exposed to the room will be more efficient. Last year member Doug posted a chart listing surface area vs. BTU radiation. If both stoves are consuming the same coal at identical rates, the one with larger surface area and lower exhaust temperature is the most efficient. It could be the smaller sized stove if that stove's design allows the exhaust to contact the exposed surfaces for a longer time period especially if that stove has a large surface area exposed to the room. Larger surface area on a smaller stove is accomplished by adding finned surfaces or casting in fillets and trim convolutions to the stove's exposed surfaces.

It's just not an straight forward question to answer. Some radiant design stoves are more efficient than convection stoves. The opposite can be true. Assessing the facts and specifications under identical conditions, it's all in the stove design and how the heat gets out of the combustion gasses and into the room/air given .

 
User avatar
oliver power
Member
Posts: 2970
Joined: Sun. Apr. 16, 2006 9:28 am
Location: Near Dansville, NY
Stoker Coal Boiler: KEYSTOKER Kaa-2
Hand Fed Coal Stove: Hitzer 50-93 & 30-95, Vigilant (pre-2310), D.S. 1600 Circulator, Hitzer 254

Post by oliver power » Tue. Jan. 11, 2011 8:17 pm

I can tell you this; When I was running both, HITZER 50-93 & 30-95, they would each take a five gallon pail of coal every 12 hours. Yet, the 50-93 felt like it was putting out double the heat. The 30-95 would idle a little lower/better. I think it might be due to being a little less efficient, letting more heat go up the chimney. Having a single grate, the air is more concentrated. I never did measure the 30-95 stack temp, as it is in a shop. The 30-95 would also pick up from an idle quicker. It's a little firecracker of a stove. Where as the 50-93 is a work horse. If you want some serious heating BTU's, the 50-93 will perform. Both great stoves. If I had to choose one of the two, it'd be which ever one came closest to my heating needs. In my case, it'd be the 50-93 for the house, and 30-95 for shop. That's why I have the two different model stoves.

 
User avatar
Chuck_Steak
Member
Posts: 386
Joined: Wed. Jan. 06, 2010 9:03 pm
Location: New Hampster
Coal Size/Type: mostly nut, sometimes stove, Santa brand

Post by Chuck_Steak » Tue. Jan. 11, 2011 8:47 pm

franco b wrote:I think the smaller stove will run more efficiently because it will have a hotter fire. I also think it is dependent on the particular stoves involved.
As I believe has been mentioned, you can't use efficency in determing if the stove will do the job.

If you had a stove the size of a loaf of bread, running at 99.5% efficiency, would it heat your
house as well as a Mark II at 85%??
Doubtful.
Proper sizing is more important.
Not for getting every penny's worth of heat out of a piece of coal,
but for staying warm..

Dan

 
User avatar
lsayre
Member
Posts: 21781
Joined: Wed. Nov. 23, 2005 9:17 pm
Location: Ohio
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Lehigh Anthracite Pea
Other Heating: Resistance Boiler (13.5 KW), ComfortMax 75

Post by lsayre » Tue. Jan. 11, 2011 9:15 pm

A point well taken Dan!!!

 
rberq
Member
Posts: 6445
Joined: Mon. Apr. 16, 2007 9:34 pm
Location: Central Maine
Hand Fed Coal Stove: DS Machine 1300 with hopper
Coal Size/Type: Blaschak Anthracite Nut
Other Heating: Oil hot water radiators (fuel oil); propane

Post by rberq » Tue. Jan. 11, 2011 9:28 pm

VigIIPeaBurner wrote:Larger surface area on a smaller stove is accomplished by adding finned surfaces or casting in fillets and trim convolutions to the stove's exposed surfaces.
On my Harman Mk I, I have thought it would be helpful to weld a number of heavy vertical fins to the sides to increase radiant surface area and convection. I would probably try it, but the wife already considers the stove barely presentable on the beauty vs. ugliness scale. ;)

 
User avatar
Poconoeagle
Member
Posts: 6397
Joined: Sat. Nov. 08, 2008 7:26 pm
Location: Tobyhanna PA

Post by Poconoeagle » Wed. Jan. 12, 2011 11:23 am

From my brief time burning both the kodiak and the 507, IN Separate chimney's, I can say the 507 consumes 1/2 the coal the alaska does and puts out usable heat almost equal. the different drafts I believe is the reason for the different burn rate as well as the size of the units and the way the heat is scrubbed off of each.

so far this is an unusual winter as far as fridgid cold.... so far... ;)

 
User avatar
lsayre
Member
Posts: 21781
Joined: Wed. Nov. 23, 2005 9:17 pm
Location: Ohio
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Lehigh Anthracite Pea
Other Heating: Resistance Boiler (13.5 KW), ComfortMax 75

Post by lsayre » Wed. Jan. 12, 2011 12:00 pm

With due consideration for proper sizing (thanks Dan), if a house requires up to 75,000 BTU's of reliable output per hour on the several absolutely coldest days of the year, and you have two essentially identical stoves, with the sole exception being firebox size and that one is rated at 96,000 BTU's (input) and the other is rated at 130,000 BTU's (input), which would be the right choice to make for this case regarding efficiency (measured as annualized consumption)?

 
User avatar
Coalfire
Member
Posts: 1029
Joined: Mon. Nov. 23, 2009 8:28 pm
Location: Denver, PA
Hand Fed Coal Stove: DS Machine 96K btu Circulator
Coal Size/Type: Nut

Post by Coalfire » Wed. Jan. 12, 2011 12:55 pm

lsayre wrote:With due consideration for proper sizing (thanks Dan), if a house requires up to 75,000 BTU's of reliable output per hour on the several absolutely coldest days of the year, and you have two essentially identical stoves, with the sole exception being firebox size and that one is rated at 96,000 BTU's (input) and the other is rated at 130,000 BTU's (input), which would be the right choice to make for this case regarding efficiency (measured as annualized consumption)?
The larger one. It will give you a longer burn time. if you actually need to put out 75K at 13000btu per pound that is 5.76lbs per hour or 138lbs per day. The larger stove will give you a longer burn time. In theroy the smaller stove could do it. Keep in mind I think these BTU's are relative. for 130,000 BTU you would need to shovel 240lbs of coal a day, I don't know if that is possible.


Post Reply

Return to “Hand Fired Coal Stoves & Furnaces Using Anthracite”