stoker-man wrote:The DF520 is rated at 218K gross/188K net, and I'm not sure how they came up with that number since it has changed over the years. At 22 pounds of anthracite an hour, maximum feed, that would be 286K gross if the coal was rated at an ideal 13K per pound. With the oil gun having a 1.5 GPM nozzle, that would equal close to the rated 218K gross, which might be how the lower gross was figured.
With the Winter almost over, we used about 8 tons of coal since October 1st. That heated a glass walled, uninsulated warehouse, with 30 foot ceilings of about 10,000 sq. ft. to 60 degrees and the office to 75 degrees. I'm not so sure a boiler net-rated at 188K can really do that.
Being the 520 coal feed rate is 2.5 lbs per hr per tooth with Rice coal and the newer s-20 with the longer gear motor arm can go to 10 teeth max feed rate is 25 lbs per hr 25lbs x 13000 btus per lb hr is 325.000 btus going in now subtract 15 to 20% for heat loss. At 15% is 39.000 btu loss is 286.000 btu out put 20% heat loss is 65.000 btu is 260.000 btu out put .
22.5 lbs per hr is 9 teeth is 292.500 btu input subtract 15% heat loss 43.875 btu is 248.625 btu output At 20% heat loss
is 58.500 is 234.000 btu output .
The older 520 with the older s-20 that used the shorter gear arm had a max feed rate of 8 teeth 2.5lbs per tooth = 20 lbs
per hr max with Rice coal your btu's out put will be lower with less coal on max feed rate .
Buck wheat size coal is 2 lbs per hr per tooth when using it in 350 & 520
The s-15 had a max feed rate of 6 teeth 15 lbs per hr with rice smaller pot with a shorter gear motor arm buck is 2 lbs per hr per tooth .
All of efm's will burn 80 to 85 % efficient when they are set up correctly and are cleaned out on a yearly or bi yearly basic
depending on the coal Quality your putting in to it