Does Stove Temperature Change Efficiency of Coal Burned?

It seems in past posts people feel running a stove a little warmer results in better heat output and more efficient coal consumption. Are people finding this true? If so, will I actually use less coal running the stove a little hotter?

I ask because I may try to draw some cooler air from my basement to the upstairs in hopes of raising the temp down there. Plus I like a warm house and if it's going to save me $$$ then why not? Thanks

I don't know on that one sd--I run mine hot some, hotter some, not so hot during the cuff seasons & still go through 3 TON per season no matter what--I'd get that hot air moving no matter what you choose to do. Like you, I keep the house nice & toasty at least 72*--what's your temp downstairs compared to upstairs?

Yeah they seem to be more efficient at moderate burns than when they're dialed way way down ... but, yeah ... like Fred said.

Back when I was running the Mark III full time, I couldn't be bothered with fine adjustments. I just set it to where we were warm, and that was that. Used to go through a *censored*-ton of coal though. Thankfully this new-to-me stoker is using about 1/3 less coal than the Harman was.

I asked because I want to run insulated duct work with an inline fan to draw up some of the cooler air from my basement utility room where my water heater is in hopes of raising the temp down there. (I have a heat-pump water heater and they are more efficient in a warmer room).

I'm going to try the duct work. It would just be more of an incentive if running stove a little hotter would benefit me.

That's a tough question. Yer sure to get a variety of opinions. It kinda depends on what you want to call a low fire. A low fire to me is when it's in the 50's outside and I'm idling thru the day. Medium fire is normal winter temps and a high fire is when it's below zero.

Also depends if your stove is a little over or under sized for the space your heating.

To me, efficiency seems linear between a low and medium fire. But between a medium and high fire, it seems that efficiency falls a little. At high fire I believe a bigger percentage of heat is inevitably lost up the chimney.

skobydog wrote:It seems in past posts people feel running a stove a little warmer results in better heat output and more efficient coal consumption. Are people finding this true? If so, will I actually use less coal running the stove a little hotter?

I ask because I may try to draw some cooler air from my basement to the upstairs in hopes of raising the temp down there. Plus I like a warm house and if it's going to save me $$$ then why not? Thanks

what you can do is, install a grate or ductwork to push the heat downstairs, using a fan. You'll have to force the air to move somehow because the hot air won't want to go downward by itself, it will want to rise.

everything I've seen shows burning it warmer will use more coal, but also makes the chimney draft better

you'll get the best mileage from coal running it on the edge of just slightly higher than where it would go out, that is usually too low a setting for a cold NEPA winter day sub-freezing.

Lightning wrote: To me, efficiency seems linear between a low and medium fire. But between a medium and high fire, it seems that efficiency falls a little. At high fire I believe a bigger percentage of heat is inevitably lost up the chimney.

I think I may have answered my own question. I increased my air intake a little last night and not surprisingly used a bit coal with more ash. I went from a low/med fire to a medium fire.

I just didn't know if there was a certain temp that favored coal for an efficient burn.

I can't complain though, the house is evenly warmed unlike a wood fire. I'm still dialing things in going from an exceptable temp of 70 degrees to a warmer 72-74.

From my limited experience a hotter fire equals more coal burned, who would have thought?

BTW, the first thing I do when I get home is run to the house thermostat to look at the temperature. I still can't believe the house is within a degree or two from when I left for work earlier that day. Try that with a wood stove

Sure, you'll burn more coal for more heat. But there is a point where heat transfer doesn't keep up with the heat that's produced. That's what I was getting at lol.

The stove is on the first floor and you want the basement warmer...Hmmm let's see. Is there a way to pipe the basement cooler air very close to the air inlet on the coal stove there by making room for the warmer air to be pushed in the replace it? Air has mass and cooler air is heavier i. e. a cool air balloon sinks Give that some thought and come up with a plan.

Lightning wrote:Sure, you'll burn more coal for more heat. But there is a point where heat transfer doesn't keep up with the heat that's produced. That's what I was getting at lol.

I understand. With the stove I have I should be warm with running it a little over "half-speed" for the majority of the winter.

If your objective is to get warm air to the basement, my thought is to push the warm air down there instead of pulling the cool air up to the first floor. Otherwise, warm air may not go down there on its own due to outside air infiltration into the basement.

I do think that if you duct it out--the only difference you'll have is warmer where you're sending it, I don't think it will affect where the stove is temp wise. Nothing ventured, nothing gained:)

Without pretending to be a coal expert though if I can find them I have a couple of texts that mention them, probably a quest for tonight.. The best thermal is usually with the greatest delta T ( difference in temperature). That said there is also combustion efficiency usually measured using net stack temps( stack temp - ambient temp) vs. CO2 content, low stack and highest CO2 is the winner. Together they add up to the total efficiency. I need to find my combustion test kit from the 70's when I was a boiler tech state licensed. No doubt does not answer your question directly but possibly points to the variables involved.

Lightning wrote:If your objective is to get warm air to the basement, my thought is to push the warm air down there instead of pulling the cool air up to the first floor. Otherwise, warm air may not go down there on its own due to outside air infiltration into the basement.

This.

If your house is not really air tight, and not just the basement, but the upper levels also, it probably wouldn't work without forced-air duct work. With air leaks, your house wants to be it's own chimney.

The only way you'll get the lighter warm air to go down into the basement is by, either creating a pressure drop in the basement that is greater the pressure difference between the warm air above and the colder air of the basement, which would likely be impossible to accomplish without some very expensive equipment. Or, a ducted fan system to force warm air down near the basement floor.

As far as running the stove hotter to maximize output, what works for others very likely may not work for you.

However, you could measure your stoves stack temps verses your room temps and try different stove settings. Then put those numbers on a graph. That may show that your setup has an optimum "sweet spot" and what damper settings are needed for it.

That's what I've been doing for my kitchen range for the past couple of weeks. Writing down stove, room, and stack temps and the corresponding manometer readings, at various damper settings to see if there actually is a sweet spot for this stove with this chimney setup to get the most heat in the house for the least heat going up the chimney.

Paul

All good points being made here.

To add, I'd not waste any money on the in-line duct fan...you will be terribly disappointed.
Get a used fan from a furnace tear out/replacement...contractors remove the old furnaces from jobs and they go in the trash...many have blowers w/ lots of life left in them.