Coalpail.com Forum

I have a setback thermostat on my Harman Mag stoker, at night I have it set to 66 deg and 72 deg during the day. In the morning it takes a while to get back those 6 deg's. Think its more efficient to maintain 72 deg 24/7 or let it drop to 66 deg at night?
Stay warm, Jimmy

ya know I always wonder that myself. I've come to the point where I just leave mine alone. It's set at 72 all the time 24/7. last year I'd set it back during the day a few degrees but coal's a slow learner and it takes awhile to get back up to temp.. So for me I leave it alone.

I agree with Wenchris, it seems to take awhile for the coal to catch up, so I leave mine alone or even turn it up because of the cooler temps at night. I don't have a thermostat for the stove so I have to experiment a bit with the settings and I'm learning all the time.
I don't know if its more effecient to leave the temp alone but I do know it's alot more comfortable.

I'd agree with just leaving the thermostat at set point. I've used this recently in another thread to make a different point but to me it's like pulling up to stop light in your car and turning it off. I don't hink your saving anything and if you are it's probably not much...

Figure 10 degree night, night is 9 hours long, the walls have a combined R value of roughly R-6 (R-19 insulation plus 14% windows with an R value of 2 or so). 1500 sqft of wall space (roughly 60x33x8).

72 setpoint: 72-10 / 6 = 10.33 BTU/sqft/hr * 9 hrs * 1500 spft = 139455 BTU
66 setpoint: 66-10 / 6 = 9.33 * 9 * 1500 = 125955 BTU

Difference of 13500 BTU, or roughly 10%. And that is probably pretty conservative given that it doesn't take into account if you have only single pane windows, a second story to the house or a larger floorplan or one with longer or taller walls, a drafty house, or the ceiling/roof and floor/basement heat losses or if you have more window space percenage than I used. It also doesn't account for uneven heat distribution in the house, partcularly the case if you depend on radiant or natural convection currents to spread the heat in the house instead of ducts and forced air. The acutal BTU savings will likely be somewhat more when all the rest is taken into account.

If it takes more BTU than that to make up the difference in the morning then it isn't worth it. In the case outlined above, that's roughly 10 minutes of additional full feedrate on time on a 85% efficient 90,000 BTU/hr stoker depending on the actual BTU difference overnight. However the actual BTU difference one would observe is probably somewhat higher, perhaps as high as 3 or more times, leading to 30 or more minutes of additional full feedrate on time. Additional meaning in addition to the on time that would be needed each hour to satisfy the normal heatlosses at 72 degrees during the morning.

With only a 6 degree setback it may not be worth it. It can be worth it though with larger setbacks (say 8 or more degrees lower than daytime) or longer setback time spans (if you can do night and during the day if your house is empty, for instance). Also, the colder it is at night the more benefit you'll get from using a setback.

I had to read that twice. But it sure looks like leave it alone to me.

We have a setback digital thermostat on our stoker, but lately, I have been just putting it on HOLD at a certain temp, keeps it pretty close to set temp within 1-2 degrees. usually overshoots a bit, but makes it nice and warm. If we leave for extended periods like overnight, I will set it back 4-5 degrees or more, just to keep the chill off and not burn as much.

Coaledsweat, that got a laugh, I had to read it twice as well.

Paul, with the coal-trol, with say a 8-10* differential would the controller call for full feed untill the higher set point is satisfied, or is the increase in feed adjustable??

I'm thinking [dangerous, I know] that if you had a desire for 72* at 7AM, but could set the controller to start ramping up the feed at 6AM [from 64*] and increase the feed at a slower rate, would this not decrease the extra coal needed to reach the higher set point??

It is a bit technical at first glance, and second, but the light is starting to glimmer on the third read.....

thanks, Greg L

.

It is a bit technical at first glance, and second, but the light is starting to glimmer on the third read.....

Greg, I hope it's not a train

Gonna leave it at 72 deg 24/7 and see how it does. Thanx
Stay warm, Jimmy

pvolcko wrote: ... SNIP
In the case outlined above, that's roughly 10 minutes of additional full feedrate on time on a 85% efficient 90,000 BTU/hr stoker SNIP ...

Is the 85% number the measured combustion efficiency of the stoker or just a guess?

Yanche

I actually run my coal-trol the opposite, 75 at night and 72 during the day. That way the stove gets to rest when it is warmer out and then work the night shift.

Yanche: It is a guess. Most manufacturers claim between 80-85% efficiency I believe.

LsFarm: The kind of adjustment you describe is not available as a user option on the Coal-Trol Digital. However, there should be no need to do what you suggest since the Coal-Trol will ramp to the needed feed rates. If one can get to the new setpoint by running at a given feedrate for 20 minutes instead of running at a little lower feedrate for 40 minutes the same amount of fuel will end up being used, you are just taking longer to get to the desired new temperature.

Coaledsweat: For your case, with only a 6 degree difference, you may be right.

The only thing I do is to turn down the thermostats on two of the three zones and let those parts of the house cool a bit overnight, No need to heat the family room to 70* when I'm in bed at the other end of the house.
I have no way of measuring any gain or loss from this, it just seems to make sense.

Greg L

.