Need Help Understanding 'Baffles' in a Coal Stove

In a coal stove / insert, does a baffle increase burning efficiency?
does it increase efficiency in extracting the heat from the fire to be radiated/convection out into the room?

I am shopping a for coal insert, but am having difficulty in comparing the different coal inserts available. I have shopped firewood inserts and pellet inserts; firewood inserts use baffles and as I understand it enables the units to burn more completely than of older designs; pellet inserts use baffles and as I understand it enables them to extract more heat from the fire before the exhaust leaves the unit.

Some of the coal inserts/stoves are hopper fed, which seem to lack baffles completely, presumably to make room for the delivery of coal from the hopper. So in the case of hopper fed coal stove/insert, is the consumer sacrificing the benefit of a baffle for the convenience of the hopper?

Welcome to the FORUM my friend. If you're concerned with efficiency, in my opinion, an insert is NOT the road to travel. Can you fit any kind of free-standing stove on your hearth area?--Some pix of that area would be real helpful.

First, avoid an insert if you possibly can. Installation with proper regard for maintenance becomes harder and because it is buried in a fireplace you have to rely on fans to move the heat.

The purpose of the usual baffle you see is twofold. It reflects heat back into the fire and then helps to direct flue gasses closer to heat exchange surfaces instead of going straight toward the stove exit. Wood is composed of half gas which is released quickly on heating. The stove is overwhelmed and if air is restricted it smokes which is unburned carbon. Adding a baffle with a perforated pipe on its front edge supplying hot air goes a long way toward burning the smoke.

Anthracite coal does not burn that way. It is capable of long slow air restricted burns without smoke. The gas in coal is only about 5 percent instead of 50 percent. Because it can be controlled and doesn't go crazy like wood, a baffle is less important, though still desirable. The advantage of a hopper and thermostat are well worth sacrificing a baffle. Faster easier tending, and more uniform heat output.

franco b wrote: The advantage of a hopper and thermostat are well worth sacrificing a baffle. Faster easier tending, and more uniform heat output.

I don't believe that you are sacrificing anything with a stove like my 50-93 as the hopper acts as a baffle when installed. With no hopper in my stove the heat rises straight up & out the back with no restriction other then an MPD if installed. With the hopper in place & filled with a load of coal which is sitting right on top of the burning bed of coal the heat is forced to travel around the hopper & out through a much smaller space between the hopper & the outlet hole.

> avoid an insert if you possibly can
Understoond; we purchased a mid-1970s house with brick fireplace in the center of the house; the way the house is constructed it is partially supported by the structure that the fireplace is built into. The fireplace is unused, and an insert would fill that void. A stove would be preferable and more efficient as I understand, but take up valuable space. In a future life, I will build a house without a fireplace and install a stove instead.

> Can you fit any kind of free-standing stove on your hearth area?
The hearth is elevated from the floor and shallow ~ 16" from the edge to the opening of the fireplace. Setting a stove on a pad on the floor in front of the fireplace would put right in the middle of the room and in the way of the foot traffic from both ends of the house.

> The gas in coal is only about 5 percent instead of 50 percent.
> Because it can be controlled and doesn't go crazy like wood, a baffle is less important, though still desirable.
Thank you, that explains what I have been seeing.

> The advantage of a hopper and thermostat are well worth sacrificing a baffle.
The Keystoker HF70 and HF90 has a description of "The stove is equipped with an automatic thermostat to regulate the air flow used for combustion, set by your touch, then controlled by stove temperature to provide a steady source of even heat for maximum comfort." Is this what you are referring to when you say 'hopper and thermostat'?

I have seen stoves that had mechanically controlled hoppers, but one of the inserts was gravity fed, the Hitzer 503. How does this compare to a 'hopper and thermostat' combination?

> Faster easier tending, and more uniform heat output.
Is a hopper style technically less efficient then?
I certainly see in the hopper style the less fuss in maintaining the fire.
Can you explain your explanation of 'more uniform heat output' for hopper fed coal?
Why would a hopper of coal be more uniform?

Thanks everyone!

The hopper keeps the coal bed topped up to full height. Without a hopper the bed will burn down over night, smaller fire in the morning can be more difficult to resurrect when you add fresh coal. Fire burns down/temperatures drop. Full bed of coals/temperature is consistent.

Hopper & thermostat on a hand feed is referring to the bi-metal thermostat that controls the rear draft door. Set it with the knob to a certain position & the spring will open & close the draft door to maintain that setting/temp.

That Keystoker70/90 is a bit different. They use a Honeywell wall mount thermometer to control the draft door. Not sure how that works or if it still functions if you lose power.

Lots of questions which is good.

The preferred way to install a free standing stove into a fireplace is to go into the chimney above the mantle rather than through the damper. If you lack the room or it would be too awkward then you have no choice other than the insert. I can understand that. Some stoves like a Crane 440 or a Franco Belge could probably fit on that 16 inch hearth. Would need some floor protection in front. Might not be big enough for your needs.

Yes, by thermostat I meant the bi-metal controlled damper to control combustion air.

With stokers the coal is fed from an external hopper to the fire by mechanical means. With a hand fired stove the hopper is internal and gravity fed. Coal will only be fed when the burning coal under it collapses to ash or primarily when the ash is cleared when the stove is shaken down.

When loading coal in a stove with no hopper the coal is cold and heat output will drop until that coal absorbs a lot of heat and ignites. Recovery time can be much longer than feeding hot coal from a hopper. The hot coal from a hopper will already have some of the gasses burnt out of it and the rest will almost immediately start giving off its gas which hopefully will burn. If there is also a thermostat it will have opened somewhat to compensate for the lower heat output at the end of a burn when the coal bed contains more ash. This helps to burn the gas and lowers any chance of puff back from accumulation of unburned gas . The completely manual stove needs a little more nursing and usually about 15 minutes as opposed to one minute to shake down and re-fill the hopper. The thermostat setting remains unchanged unless you want more or less heat output from the stove. the hopper stove should be more efficient in terms of burn efficiency. Fred made a good point in pointing out that the hopper in his stove also acts as a baffle. The 503 lacks a thermostat which means manually adjusting the air when re-loading and then setting again for a long burn after burning off gasses.

> When loading coal in a stove with no hopper the coal is cold and heat output will drop until that coal absorbs a lot of heat and ignites.
> Recovery time can be much longer than feeding hot coal from a hopper.

Is this because you would be feeding the new coal onto the top of the pile, that it has time to warm up before reaching the bottom where the fire is at?

Along this line: In a front loading unit, once the coal fire is started, wouldn't you load it up so that it has a pile similar in regards to how a hopper is feeding? Granted without a hopper the pile would not be as high. I ask because all of the pictures of a front loading coal stoves always show a level bed of coal.

The coal in a gravity feed hopper is inside the stove directly over the burning coal bed so it is at stove temp not room temp or outside temp like the coal that you would manually load.

The hopper is continually feeding the coal bed so it never lowers unless the hopper runs dry. When you manually load you need to build the bed back up but you have to be careful that you don't smother the fire, especially when it's weak after a shakedown. You'll likely need to spread several thin layers across the entire bed before you are done unless you regularly add coal throughout the day & night. There is no beating a gravity feed hopper for convenience & the ability to sleep through the night & be toasty warm in the morning.

Earlier on, JohnB mentioned something about a MPD? What is an MPD?

>With no hopper in my stove the heat rises straight up & out the back with no restriction other then an MPD if installed.

Aside from that, not that I have made a decision on what manufacturer and model to purchase yet, but to simplify my question: between the Hitzer 503 (gravity fed hopper), and the 983 (manual front loading), is the burn time significantly different?
I get that the hopper fed provides consistent heat, and that given regular attention requires less time to continue the burn than manual loading.
If a hopper fed is consistent heat, then a manual front loading has a heat output cycle somewhat like burning wood (but over a longer smoother curve)?

How often does a 503 needed to be tended in a day? once / twice / three?
How often does a 983 needed to be tended in a day? once / twice / three?

Disclaimer: I've never used a hopper..

But just wanted to clear up a couple things about a "front loading" appliance.

gardener wrote: I ask because all of the pictures of a front loading coal stoves always show a level bed of coal.

A front loader can be mounded up in the center just as high as a hopper fed would have. I often do this.

JohnB wrote:You'll likely need to spread several thin layers across the entire bed before you are done unless you regularly add coal throughout the day & night.

I've loaded over 70 pounds at one time and regularly add 50 or more at one time on top of only a few inches of burning coal, completely covering the burning coal left after shake down by 7+ inches, no burning coal is left exposed. I load at 24 hour intervals and don't touch in between.

gardener wrote:Earlier on, JohnB mentioned something about a MPD? What is an MPD?

Stands for "Manual Pipe Damper" which is installed in the flue pipe. It's a butterfly valve that is rotated manually to restrict the flue gases exiting the stove. They limit, to an extent, the strength of the negative pressure in the stove cavity which has many desirable effects.

gardener wrote:If a hopper fed is consistent heat, then a manual front loading has a heat output cycle somewhat like burning wood (but over a longer smoother curve)?

Not really.. The burn cycle of a front loader can give off a steady heat output thru the entire burn cycle with a properly adjusted bi-metallic thermostat or the use of a barometric damper. The only time heat output falls is after loading until the fresh load ignites, which is usually less than 30 minutes.

I'm sure hoppers have desirable attributes.
This is not any attempt to persuade otherwise.

I've owned a Hitzer 503 for 6 years and love it. I bought it to off set heating cost when heating oil went through the roof. I was hoping it would at best decrease my cost by half but it works so well that I rarely have to run my furnace at all. My house is an 1860s model two story farm house approx 2300 sq. feet. True for most efficient heating you do need to run the blower fans when temps drop into 30s or lower but soon you get use to the blower noise. When I've lost power I have to crank the stove temp hire but it still gets the job done. The hopper is the way to go. It increases burn times and makes tending much easier. I tend my stove once every 24hrs. when temps are in the 30s or higher and every 12hrs when colder. The stove temp is controlled with the primary air setting on the ash pan door. There is no thermostat. You soon learn through trial and error how much to open the vents at any given outside temp to get your indoor temp where you want it. A stove thermometer is a must to facilitate this. The 983 has no hopper but a bigger fire box. The bigger fire box allows for larger logs if and when you burn wood and the stove is rated for higher BTU output. I still feel the hopper on the 503 makes this unit more desirable but you will have to assess your needs to decide.
Gian4

Lightning wrote: I've loaded over 70 pounds at one time and regularly add 50 or more at one time on top of only a few inches of burning coal, completely covering the burning coal left after shake down by 7+ inches, no burning coal is left exposed. I load at 24 hour intervals and don't touch in between.

Good luck with that approach in a 50-93! If you didn't kill the fire completely the coal gas bang shortly after that rear flap closed would shake the entire house. Do you have an over fire air intake?

JohnB wrote:

Lightning wrote: I've loaded over 70 pounds at one time and regularly add 50 or more at one time on top of only a few inches of burning coal, completely covering the burning coal left after shake down by 7+ inches, no burning coal is left exposed. I load at 24 hour intervals and don't touch in between.

Good luck with that approach in a 50-93! If you didn't kill the fire completely the coal gas bang shortly after that rear flap closed would shake the entire house. Do you have an over fire air intake?

There are ways to prevent puff back. Its a matter of keeping the volatile gases diluted until the fire works its way up thru the fresh coal to ignite them. Just keep the load door cracked a quarter inch until they ignite.

I did install my own secondary air distribution pipes, but the cracking of the load door works too.

I'm not refuting the use of a hopper, just saying its not so bad not to have one.

There is a big difference between the modified coal furnace that Lightning refers to & the coal stoves/inserts that the OP has asked about ! No sense in confusing the issue further .