Low Load Capabilities of the Coal Gun

While ideally two 2 S130's would be the best solution, there is the initial cost difference to consider. We estimate that you need to burn an average of 1/2 lb to 1 lb of coal an hour in order to sustain a low load fire. That would translate in BTU's to somewhere between 7 and 15 thousand BTU's per hour. However, we have had customers go long periods of time with much less demand.

Thus, your solution, in regards to summer usage, would entirely depend on the amount of demand you have for DHW.

Hi folks, I am new to this forum. I have an AHS S130 burning buck coal going on three years..... I absolutely love it. I heat 5,200 sf of house and garage. My issue is with low demand, and the fire going out. It did it again last night. The temp was around 60 yesterday, and I assume the house didn't call for heat. When I returned home at 11:00 the fuji controller showed an ash temp of 87, and the unit was stone cold. I have to believe that one of the 4 zones in the house or garage had called for heat in the previous 12 hours. My house and garage are very well insulated, but people are talking about running these units all summer for domestic HW. Any ideas as to why the fire would go out. It's a real pain shoveling 400 lbs of coal out of the bottom of the unit!

Have you tried burning the recommended pea coal in the boiler? Since it's larger, it would pack less and allow more natural air to get to the coal in an idle fire.

That said the AHS does not have an idle keep alive timer or a well though out control system for low demand conditions. Your well insulated home makes the problem worst. The heat radiation loss from the boiler is low, because your house is well insulated. This keeps the boiler water temperature up for a lengthly time at idle conditions. Therefore, the aquastat low limit is not reached before the fire goes out. My AHS boiler does not have the thermocouple controller. When it was first offered I thought it was a method for solving the idle fire problem. But, that is not the case, it's just an different method of measuring ash temperature. It's direct probe measurement rather than the infrared radiation method used by A-A.

Possible solutions would be to increase the idle heat loss from the boiler by raising the boiler aquastat setting or making the boiler room open to colder air. Another solution would be a idle timer that periodically turns on the blower, to refresh the fire. In your well insulated house this would also likely have to be linked to a heat dump zone. The ideal solution would be a much more intelligent control system.

Yanche, thanks for your response. I have always used the buck as that was what I was told when I bought the unit. I might try some pea in the early spring, as I just put 8 tons of buck in my bin, and this won't be a problem as it gets colder. I purchased a timer just as you suggested but have yet to install it. My thinking was to hook it up to the biggest zone, and let it dump for 10 minutes every 6 hours. Maybe your idea of hooking it to the blower would be better as it would dump automaticaaly when it needed to.

Here's a picture of the Anthrastat in a AA130. Inside it doesn't get much simpler than this. Appears to be bimetal, a thread for adjustment, and a microswitch.Patent number 2815415 if you have a way to look patents up online?

In this case we would suggest the 260. You shouldn't have an issue with low load. The larger mass of coal should keep the fire going without demand for extended periods. Our S500 sometimes goes over twelve hours without running at all, yet the fire never goes out.

Also, allow me to explain how the ash monitoring system assists in low load situations. When the ash temperature drops and the grate moves, this results in a rearranging of the coal. This movement provides new air routes through the mass, along with new fuel and oxygen. We have found this to be very effective in maintaining low load fires.

Geeeze, buying a whole new boiler, a larger one, especially when the 130 a bit more than needed, seems to be an extreme remedy for the occasional outfire. I think going to pea coal would solve the problem for the most part. My buddy that installed a Coal Gun 130 two weeks ago is burning pea and had no outfires so far. It has been very warm this last week. His only demand has been DHW.
He is thinking of installing a fan limit switch (see photo) in the stove pipe to sense an outfire and shut the boiler down. At least if he has an outfire he won't have a tub full of unburned coal.

If the combination of the three loads requires an S260, then that is what I would go with. It seems the conversation has left out the fact that, according to the TS, he needs a 260 to actually meet his need, but is worried about the times when the demand drops. In that case, the 130 would be find for Steamup's low load, which is actually not low for the S130. However, when heat was needed in all three areas, the S130 wouldn't be sufficient. Considering all these factors, with the information given, the 260 seems to be the logical choice.

Thanks for all of the input. Based on all of the information I have recieved, I have decided to take a slightly more complicated route. I am planing to install the smaller 130 size boiler to optimize efficiency.

I am also planning to install a 500 gallon storage tank with heat exchanger in the basement of my house. Heating this tank of water on a weekend in the summer will provide me with a heat source for my domestic hot water all week long. I hope to fire the boiler only on one day of the week during the summer.

The second use of the tank will be in the winter. I will heat the tank to maximum before going out to the workshop. The tank then can "flywheel" the house while heat is diverted to the workshop. The 130 should be sufficient for the workshop on all of but the coldest of days.

I will start another thread an post pictures when I get started.

Steamup:

You will only be able to get 4.6 days @ 100 gallons/day of hot water with the 500 gallon

storage tank and no loss,more like 3 days realistically with good insulation.Also the curve

of the heat available goes down as your deplete your stored heat so a long recovery is

needed late in the cycle of heating. I did the calculation based on 500 gallons,92* temp

rise in tank from 120* to 212*,and 100 gallons of heated water per day.

BigBarney

BigBarney,

You are correct but I only use about 50-60 gallons a day of hot water on average based on past propane bills, so running a week on a 500 gallon storage tank should be enough. If is not, the propane water heater will take over. The storage tank in the 80 to 120 deg range still has the ability to preheat the incomming 50 deg. F. well water. If I reduce my need for propane for hot water by 80 to 90 percent, I will be happy.

Same thing with the flywheel effect on the heating cycle. If I more heat than one boiler will put out, I will fire the oil boiler for the few hours a year I will need it.

My savings on domestic hot water using coal will only be about $25.00 to $30.00 per month. Larger storage at this time is not economical.

I have been running a S-130 and found it to be easy to control under low load conditions. You should not have any problem if you have a fairly constant hot water load. I would recommend lowering the aquastat setting to 150-160 degrees. You should also have at least one dump zone and set the temperature for 200-210 degrees. This will give you enough differential to handle substantial BTU gains with out dumping. The hot water storage tank is the best dump zone but you should install a mixing valve on the supply to control the elevated temperatures that can occur.