Slow1 said:
Backwoods Savage said:
Okay, it conducts heat faster. Question, if two stoves have the same btu's in the firebox, will a steel stove produce more btu's than the soapstone stove? If so, where exactly would that heat go from the soapstone stove? Certainly not up the chimney with the low flue temperatures we get. Simply put, I do not think you will get more btu's from steel or cast or soapstone. I think you will get the same amount of btu's. Otherwise where would the heat go? It has to go somewhere and I think it was Todd stated the heat would go toward the cooler room air. Makes sense to me.
Perhaps the answer is in the rate at which these BTUs can be released to the room. With a steel stove perhaps they could be more rapidly released to the room than with an otherwise identical stone stove - if this were to be true then I would expect that the fuel load would be more rapidly consumed in the steel stove if all other factors (flue temp and velocity of gases up said flue) were held constant. Total energy released from two (theoretical) identical loads in the two hypothetical stoves would be the same, but one would finish first, the other would have a longer burn time.
EDIT to add -
IF the same two hypothetical stoves were to burn these identical loads at the same rate (adjust air or whatever) so that the fire burns for the same length of time and again the flue temp and gas velocity is identical, then we accept the statement that steel conducts the heat faster than the stone. I would expect the steel stove to begin releasing the heat to the room sooner than the stone (i.e. warm up faster) and perhaps reach a higher peak temperature (depending on the burn profile) than the stone. The stone version of the stove I would expect to heat up slower and not peak as high but then release the energy for a longer period of time after the fire has died out. Again - the total amount of energy released to the room I would expect to be the same.
The amount of the heat that a stove actually transfers to a room depends on a number of factors:
1.
Combustion efficiency.
How well the stove converts the wood to carbon dioxide and water, minimizing the production of other substances. Hotter and dryer is better.
2.
Heat transfer efficiency (thermal efficiency).
How much of the firebox heat goes up the chimney into the atmosphere (stack loss) depends on the firing strategy and the thermal mass of the heater. Metal stoves and fireplace inserts with firebrick lining are designed to be clean burning but still have poor thermal efficiency because they lack a thermal mass that functions as a heat exchanger. Soapstone slabs in sides and tops of some models do not qualify as "thermal mass" heaters. They fall short on mass.
Combustion efficiency multiplied by the heat transfer efficiency, is the
overall efficiency, but this term still does not fully characterize the true efficiency of a heater. An IDEAL wood heater has high combustion efficiency and "moderate" (not "high" as with an all metal stove) heat transfer efficiency. Soapstone, or other masonry, is sometimes added to an otherwise all metal stove to "moderate" the heat transfer efficiency.
3.
Linearity of output.
For clean combustion, wood requires a brisk, hot fire which results in short burn times. If the heater has no storage capacity, as in metal and metal/soapstone combos, the fire must be damped, otherwise all the heat is transferred into the room during the burn time not to mention over firing the stove or losing the heat up the chimney. Thus, the room becomes overheated while the fire is burning and under heated after the fire has died down. An overheated room loses more heat to the environment because of the higher temperature differential between the room air and the outdoor air.
4.
Partial charge efficiency.
Most metal and metal/soapstone stoves do not handle small fuel charges efficiently because high temperatures are needed to obtain non-smoldering combustion. In the milder days of the heating season when only a partial charge is required, burning smaller fuel charges is the idea but some stoves, simply put, are not designed to do this.
In short, soapstone paneled metal framed stoves act like a mini-heat bank but do not have the mass of a thermal mass heater. They warm up slower, bank some heat and cool down slower than their all metal cousins. Neither fire box nor stove can take the full bore full air supply to burn a full fuel load without dampening.
This help?
Aye,
Marty