To better understand, let's cover some basics. These furnaces are called multi fuel units because they can burn wood, bituminous (soft) and anthracite (hard) coals. Truth is, since they are designed for multi fuels, they aren't set up for anthracite to get the best results. They simply need a minor modification and a somewhat specific shake and load routine.These three different fuels have their own combustion requirements. Wood and bituminous are similar in that they both need a fair amount of secondary combustion air thru their burn cycle. Secondary combustion air is air that comes in over the fuel bed to burn gases as they are baked out of the fuel. Anthracite has only a small percentage of these volatile gases. They are baked out shortly after loading, making secondary air not quite so important thru most of the burn cycle. Anthracite likes most of its combustion air from underneath, up thru the grates. This is primary combustion air.
In these particular units the secondary air is provided two ways. The first way is thru the vents on the load door. The other way is not so obvious. There are two plates located at each end of the fuel bed called the front and rear liners. These liners have air passages for primary combustion air (air coming in under the grates) to bypass the fuel bed and come up over the fire. I believe the manufacturer used this design to guarantee some secondary air if the load door vents where closed. Since anthracite requires it's air too come up thru the grates, this design doesn't work very well. Here's why; as anthracite burns, ash begins to accumulate on the grates. As the grates get covered with ash, the primary combustion air gets blocked from going up thru the grates and is then rerouted around the coal bed later in the burn. Its the case of, "path of least resistance". You've most likely seen this happen if you have tried to burn anthracite. It results with loss of heat output or a dead fire before the coal bed uses half of its fuel. Its also likely you are cleaning out the fire box every few days to keep a decent fire going with good heat output.
Don't despair, there is an easy fix. It only requires some fiberglass insulation between the liners and the fire box wall. And no, fiberglass insulation will not burn. Use insulation that is about an inch thick. Cut a strip about 24 inches long and 2 inches wide. Wrap it around the top back side of each liner, secure it with tape for the installation. Pinch the fiberglass insulation between the liner and fire box wall as shown in the pictures. This seals the ash pan area so that primary air has no choice other than up thru the fuel bed. This is the single most important modification needed for burning anthracite.
Next, let's look at the grates. A few things worthy of mention. Firstly, it appears they are symmetrical, but they are not. They do in fact have a top and bottom. The bigger openings in the grates need to face downward. This orientation is needed so ash doesn't become compacted in the grates' openings. Also the grates will sit lower in the frame which improves clearance to help prevent coal jams. I ran mine with the grates upside down for three months. Things went much smoother for me after this discovery.
For more information on the grates upside down..
Grates Upside Down
Secondly, on the bigger units with two inline grates, there can be some slop where the two grates join in the center which prevents good ash evacuation in the back of the fuel bed.
For more information on fixing slop between the inline grate system..
Fixing Play Between Inline Grates
Thirdly, its very easy to break the grate nub that the handle slides onto. I've broken two of them. The remedy is to slide a chunk of square steel stock into the handle to balance the twisting forces against the grate nub. I also cut an end off my ash pan so ash would slide off it easier and it also makes better access to the grates for poking and slicing underneath. Now, lets learn about shake down and load technique that will make your results even better. I've come up with a few tools, most hand made out of stuff I found at the hardware store.
Here is a snap of my coal tending artillery.. From left to right..
You will see how I use these in the video.
1) Coal Pusher
2) Clinker Buster
3) Grate Poker
4) Center Frame Slicer
5) Grate/Frame Slicer
6) Wire Fire Box Brush
7) Coal Bed Leveler
8) Flash Light (on the bottom) Here is a short video on my latest shake and load routine. I call this the "double shake". It incorporates the use of tools between shakings to better evacuate ash from the fuel bed.
I recommend the use of a barometric damper since these units don't have any way to automatically regulate combustion air. This device limits draft strength which results in a smooth consistent heat output between tending. I also feel the use of a manometer is mandatory. This device measures the draft pressure and can help diagnose issues with your appliance. It can also warn you if draft is heading towards failure so you can take steps to prevent it. Most importantly, have working Carbon Monoxide detectors in your home, at least two of them, near bedrooms.
Click on these links to see more information about some of the things you saw in this thread..
For more information about the window I installed in the load door..
Load Door Window Installation
For more information on the secondary air pipes in the fire box..
Secondary Air Distribution System
For more information about the hot water coils..
Hot Water Coil Project
For more information on the negative pressure ash can..
Dust Free Ash Pan Dumping