Coal Fire Smoldering Out Due to Poor Draft...?

I've successfully heated my house with wood for several years in my circa 1988 Stratford S1090 hand-fired dual fuel coal/wood stove but have recently been trying chestnut coal with little success. The problem is that the coal fire smolders out after 4-5 hours--- leaving unconsumed coal, regardless of how well it's going when I leave it. I've tried 2 coal suppliers, thicker/thinner wedges of coal, shaking more/less, new grates, and every venting combination possible. I'm left with the belief that this might be due to a poor draft related to an oversized flue.

Specifically, my stove of has a 6” flue collar = a cross-sectional area of 36 square inches. My outside-mounted 30' masonry chimney has a 9 X 13” terracotta liner that comes in at 117 square inches. For an outside chimney, I understand that you are supposed to keep the ratio 3 cross-sectional ratio always going to cause me problems? I should have a manometer to measure draft in a few days but what is the appropriate draft range for such a hand-fired unit?

it's just too warm, wait for it to cool down, especially with an exterior chimney.

Hello lockeal, and welcome to the forum.

The bottom line is that coal needs a lot of air, many times more than wood from my experience.

I went from a 6" chimney last year to an 8" chimney this year, and I added about 5-6' in height. The difference has been that the boiler's combustion blower rarely comes on once the fire is stable. The added draft from the bigger and better chimney is doing the job.

If you are going to do anything to your stove, I'd add a combustion blower. They are less than $100, and really help getting a fire going and if hooked up with either an aquastat [for a boiler] or thermostat for a stove or furnace, the blower can stabilize heat output as well.

I'm sure your chimney will draw much better once the weather cools down. Cooler weather is just a few weeks away!! There is a simple check for draft in your chimney and stove: when you open the loading door, with either a wood or coal fire, do you get a roomfull of smoke and fumes?? or is there just a little smoke getting out then it is pulled up the chimney?? With my earlier too-small chimney I had smoke getting out into the room in huge quantities, now I get only a little smoke when I first open the door.

You said in your post that you had tried a lot of things with your attempts to get coal to burn. I too have struggled at times to keep a fire going or not burning out.

The main thing with coal is air flow, and heat from the coal bed. You need to have as deep a fire [pile of coal] as possible. I can get about a 12 hour burn in my firebox if I heap the coal on to a depth of at least 14-16". My fire burns about an inch an hour. If you don't have more than say 6" of coal on the fire, once it burns down to a thin or shallow fire, it starts needing more fuel, the heat in the pile will drop and the fire will go out. Leaving some unburnt coal behind. The fire needs to feed on itself. A single piece of coal usually won't burn, it needs to have heat from other coal next to it.

It is rare in my boiler to have a fire burn all the way down to just ash. If I'm letting the fire burn out, there is always some coal that would have burnt longer and more completely in a coal bed that is left behind.

Your grates need to be able to let the burnt ash fall through into the ash pan as the fire is burning. Otherwise the ash will clog the grate, block the air flow and smother your fire. If you go out and shake the grates at 3-4 hour intervals, does the fire keep going? Are you trying to get a load of coal to burn all the way to ashes like you would a wood fire??

I hope some of the above is helpfull, I wouldn't reline the chimney unless nothing else works.

Greg L

I'm building the coal bed to the maximum height possible which is about 12-14" and it tends to burn down to about 8" before going out.

The draft has always been a bit erratic with wood and it certainly is tough to get drafting at startup. Opening a door near the stove usually helps and you do have to be careful to open the door a little at first with wood to avoid smoke backdrafting. When not in use, I tape up the barometric damper to avoid the backdraft taht occurs otherwise. My house is probably over-inslulated and thus very tight which is a contributing problem. I don't run any exhausing applicances except for the occassional basement dryer or bathroom fan. I'm just hoping some colder weather will help my draft and the problem will resolve itself.

What kind of "combusion blower" would I need for this stove and where would it install? The stove does have a fan on it already (pic attached)?

I did a search for your stove and can't find any information. Can you post a photo of the stove and the firebox/ash pan/ draft controls?? This will help us help you.

Or maybe scan a page from the owners manual of the exploded view of the parts in the stove. [assuming you have one]

Greg L

It was made by a company in Britain called Aarrow. I don't have an owners manual but Dussingers Stove in Lancaster has parts and claim the stove is one of the best anthracte burners ever built. Apparently Aarrow has over a shipload of anthracite brought to England for testing during the design the stove.

Here's a pic of a SC75 which is a little smaller but identical.

A slightly smaller SC75 sold on ebay recently with some pics at
**Broken Link(s) Removed**
The stove has a slider draft control in the front on the ash door and a small lever draft control on the rear of the stove. I was told only the slider draft control on the ash door should be used for coal so all the air comes from up from below.

With the sliding draft slots in the ash pan door fully open, and no restrictions in the chimney flue [manual damper open] the fire goes out with still 8" or so of coal? There are not any above-the-fire air openings right? Is the loading door gasket good??

I'd check the grates for clogging. Try shaking at about 3-4 hours. Shake 'till you see hot coals fall into the pan. If it draws for 4-5 hours then dies, I think it is ash clogging the grates.

Does the blower on the back of the stove blow air around the stove cabinet and out some heat vents?? A combustion blower would have to be added so that it blows only into the ash pan area and forces air up through the coal bed from the bottom.

The sole source of air to my firebox is the 2" diameter screened opening in my combustion blower. I'm feeding a fire that is about 60-70# of coal. Almost two 5-gallon pails of coal.

When your coal bed is burning, is there anywhere in the firebox where air can get around the coal bed?? All air must go through the coal, none can be 'sneaking' around the coal. Or getting in above the coal. [this works for wood, but not coal]

I can put out my fire by raking a portion of my grate clean of coal and letting the combustion air out and around the coal bed, The fire dies in about an hour for lack of air from underneath.

Does the stove do better during the night with cooler air temps??

Greg L

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Have you tried opening a window in the room where the stove is?? If your house is really tight, you may have to provide an air duct from outside to near the bottom of the stove to provide outside air.

If your house is really tight, the chimney is trying to pull a slight vacuum on the whole house. Open a window and observe the draft, does the smoke vanish up the chimney??

Just more ideas. Greg L

Once the wood I use to light the coal is finished, the coal continues to burn for a few hours by itself and that's it. I do my best to block all air openings so that the air has to come up through the coal which also seemed to extend the burn to a minor degree.

The door isn't 100% airtight along the bottom edge as I had to dig some of it out to get the door to latch, but I'll try digging out what's there and adding new rope gasket tonight...

I do open a door that's about 5 feet from the stove to get the draft started but since it's in my living room---I'm not real keen on leaving it open for an extended time...

The room that the stove is installed in has a 20' high ceiling that is completely open to the rest of the house, but I don't know of any effect, good or bad, that could have on draft.

LsFarm wrote:
The main thing with coal is air flow, and heat from the coal bed. You need to have as deep a fire [pile of coal] as possible. I can get about a 12 hour burn in my firebox if I heap the coal on to a depth of at least 14-16". My fire burns about an inch an hour. If you don't have more than say 6" of coal on the fire, once it burns down to a thin or shallow fire, it starts needing more fuel, the heat in the pile will drop and the fire will go out.

Hmmmm....
It's been awfully warm out the past couple of weeks ( especially today! ). I don't have a combustion blower or anything like that. I never get smoke out the door of the stove.
With this warm weather, I throw a bucket on top of the generous supply that survived the night......this brew makes for a total "red bed/new coal" depth of no greater than 10 inches. I have the draft screw almost all the way in ( it's barely open a quarter turn ). I used to go nuts with how slowly the coal reacts to changes, but now I know the range of what WILL work and what WILL NOT work. So no matter how dark the mound of coal looks, I know if the bed I started with was with "the range", I just button her up and walk away........it'll work out in the end.

Hi Lockeal, any difference with the stove's performance this last weekend with the cooler nights?

I'm thinking that a 3" duct coming up through the floor from the basement or crawlspace, venting the stove to the outdoors will make a huge difference in your stove's performance.

Greg L

I relined around the door to make sure there was a good seal and started it up again with temp at around 40.

I had the stove at about 350-400 for 6 hours, which was definitely the best I've done, but when I shook the grates and added coal it went out sometime within 2-3 hrs. It seemed to be drafting better with quite a bit of the coal burning bright when I shook it and filled it up.

There is a full basement that is vented to the main floor with a door that I can try leaving open...

Any other ideas?

Lock--

Classic problem I had for over two years. I was venting a 6" collar into an 8" square telecotta. My belief, the larger tellecotta wasn't staying warm enough to provide sufficient draft. While it would work okay in very cold temps for 6-8 hours, the fire would sometimes die overnite as the amount of usuable coal decreased. I bit the bullet and installed a 6" round ss liner. This was a great improvement but I still have some drafting problems on warm or humid/wet days.

Just the other day, I was on the roof checking out the top of the flue. With the coal stove burning at 50%, the top cap was only warm, maybe 70 F. 200 F behind the stove on the vent stack. So I had a 130 F drop in a 30' flue. And this was with SS liner!

LS is always on the cutting edge in regards to ideas. Give his ideas a try if you do not want to spend over $500 for the liner. I too have a tight home. I leave a basement window cracked open 1".