Reducing Thermostat When Not Home

I have a Keystoker Koker furnace that was installed by the home's previous owner in 2014. This is my second heating season with it and I have made some adjustments to make the house more comfortable. One improvement was replacing the original Honeywell thermostat with a new digital one. Here is my question - Is it cost effective to turn the thermostat down during the day when we are not home for more than 8 hours? I typically turn it down 4 degrees in the morning when we leave for work. When we come home and turn it back up, it has to burn a decent amount of coal to heat the house back-up. I feel as if there is a breakeven point where the amount of coal you "save" during the day is the same amount that you burn to reheat in the evening. I'm wondering if a different temperature reduction is better or by its nature, the furnace doesn't really need to be turned down and the reheating is wasting more coal than is being saved. Any insight would be appreciated. Thanks.

A period of lower heat demand will always save fuel. A stoker though does not go out, but enters a period of low efficiency combustion to hold the fire. That difference from an oil or gas fire probably makes set back of a stoker less effective than something that shuts down completely.

By keeping track of degree days and pounds burned with set back and without you could settle the matter.

As long as you don't mind waiting for the house to warm up when you return, go for it. Setbacks normally save fuel, but not everyone is willing to deal with the temperature swings.

A programmable thermostat would be a nice upgrade if you want the house to be warm when you wake up/return.

only go a couple degrees down and up and have it come back up at least an hour before you come home. I just leave mine on a set temperature. maybe drop it 1-2 degrees when we are not home, but like you said, takes so long for it to come back up to temp.

I don't think it makes sense on a daily basis. If you were going to be gone for a week, ok. But when you set your thermostat back to say 65 degrees, everything in your house including the house structure gets to be 65. It takes a long time and lots of BTU's to bring all that back up to temperature.

I run a Koker also. My experience is that a change of 2 degs is the most you want to do. Coal is much slower to react than a propane/gas furnace. At this point I simply set it and enjoy the heat when I'm home and the warmth house when I arrive.
-Len

I've played this scenario through and agree with coalkirk and CoaLen. One runs a boiler to air system and the other a furnace/stove. Once things cool down like CK said it takes a while to warm them back up with hot air. I use to change the thermostat on my oil furnace when we worked and I could really feel the heat being sucked up by the cooler house. Now I leave it set because the Vigilant keeps one room nice and warm with radiant heat while the thermostat in the next room gets fooled by about 3 degrees. When it's cold like it is now the house stays evenly warm with the furnace picking up the slack the little radiant stove can't provide.

Thanks for the feedback everyone. The reason I started to think about all of this is programmable thermostats for my heat pumps (they are obviously better equipped for the mild Fall and Spring months). Some of these manuals suggest 8, 10, or even higher degree thermostat reductions when not at home in order to save money. Of course, to get the house back up to temp., that aux heat kicks on and you are burning kWh like nothing. So what are you really saving unless you get fancy and disable the aux heat? When I did a little more research online, most installers/service techs recommend no more than a 4 or 5 degree reduction for heat pumps. Of course there are variables for every house, including comfort, insulation, alternate heat sources, etc. Just by observation, when I turn my thermostat on my stoker down 4 degrees during the day, I typically burn the same amount of coal as when I am home on the weekend and don't adjust it and weather conditions are pretty similar. I'm sure there are more accurate and complicated ways to measure all of this, but for now I'm going to go with the 2 degree drop during the workday. Let's see how that plays out the next few weeks. I'll be sure to post an update. If anyone else has any experience experimenting with this, let us know.

I think some of the comments have clouded the issue here. The original questions related to the potential for savings from setbacks. All else equal, when your house is maintained at a lower temperature it gives off heat at a lower rate than it would at a higher temperature. To get the house back to the same internal energy, you only have to replace what has been lost. Sure, if you walk into a cold house it will feel cold, and the heat will have to run for a while to warm everything up again. But the amount of heat it will take to do that is less than the amount it would have taken to maintain the higher temp (because the house has lost less than it would have at the higher temp). With a programmable thermostat you can use whatever setback you like, and through experience can learn about how much recovery time is likely to be needed. Without a programmable thermostat the setback limit is determined by your willingness to sit in a cold house for a while. Either way, you save on fuel with the setback (obviously assuming you avoid the electric aux heat), and a bigger setback gives bigger savings.

Mike

I agree, Mike, that lowering the differential between inside temp. and outside temp. lessens that heat transfer and you should be saving money as the day goes on. The key is trying to figure out that breakeven point when you have to reheat everything and the input of energy that it requires. Of course complicating the matter is how "tight" the house is, types of insulation, square footage, layout, and the list goes on. Then again, comfort might outweigh any of this in the end

There isn't a "break-even point" - during the setback the cumulative heat loss is lower than it would have been if the original temperature had been maintained. Recovery from the setback requires an extended run, but the total fuel use is systematically lower.

Mike

WNY wrote: ↑

Wed. Jan. 30, 2019 8:58 pm

only go a couple degrees down and up and have it come back up at least an hour before you come home. I just leave mine on a set temperature. maybe drop it 1-2 degrees when we are not home, but like you said, takes so long for it to come back up to temp.

Agreed maybe 3 degrees tops.

Since I have a coal troll, I tried the set-back feature at night and through the day with my LL - AK110. But like WNY commented, I figured out quickly it didn't save much coal (If any) and just caused overshoot on warm up. For me, I couldn't tell if there was any measurable savings and figured it was much better to just leave it at one constant set temp. When really cold, a 2-3 degree drop in setpoint compared to the inside/outside differential is a relative low percentage in savings even if there's no over shoot on warmup. But for me, I figured the over shoot was eating up the savings, so I just left it alone and stayed more comfortable....

Yeah I'm not so sure about some of the logic used in this argument. Save a little here and run like hell to catch up. When the thermal mass that is our homes cools down it takes a long time and lots of fuel to bring it back up. Just because your thermostat says its happy that doesn't mean the mass of the structure has returned to its previous temperature. Just that the air around the thermostat has. One of the many reasons I burn coal is so I don't have to worry about operating like someone watching the level gauge on their fuel oil tank constantly. If you are burning oil then yes the set backs make more sense as it's an intermittent fire. But with a coal fire burning constantly, not so much. We are already so far ahead of the fuel savings curve that it just doesn't make sense to me to try and squeeze out another couple bucks and give up the constant even warmth that coal provides us. I guess I'm factoring comfort level into the equation more than some. Bottom line is do what you are comfortable with but unless I'm leaving town, in which case I'd let the coal boiler go out and plug in the oil boiler , I'm staying the course.

coalkirk wrote: ↑

Sat. Feb. 02, 2019 7:34 am

We are already so far ahead of the fuel savings curve that it just doesn't make sense to me to try and squeeze out another couple bucks and give up the constant even warmth that coal provides us. I guess I'm factoring comfort level into the equation more than some.

That statement pretty much says it all!