Rob R. wrote:Hi Phil, I also live in a very windy area, in the very Northeast corner of New York State. Infiltration losses from the wind are my biggest challenge, but I have significantly reduced the heat loss of my house by replacing the windows on the wall that gets the most wind, and caulking/sealing the rest of the house the best I could. I recommend that you do the same.
As for the boilers, you can reliably get 200,000 btu's out of a 520, but the stack temperature will be higher than if you did the same job with a 700. I got the 200k number by allowing 12,500 btu’s per lb for anthracite, 20 lbs per hour for the stoker in a 520, and 80% efficiency. Yes it is true that the stoker in a DF520 can burn 25 lbs per hour, but in my experience if the coal burns a little slower than average, it is tough to get a proper burn at that setting. I have no experience running a 700, so I don't know how well it would run at maximum feed.
One thing I do have firsthand experience with is installing an EFM 520 in a house that was previously heated with a 105k btu oil boiler. It is my dad’s house, and the oil boiler used to run about 15 hours per day when it was zero and the wind was roaring. The EFM has no problem holding the house at 72 degrees on 4 teeth of feed (50% output) in the same conditions, and it runs about the same amount per day. I could increase the feed rate so the stoker didn’t have to run as much, but a -20 day doesn’t happen often enough to justify changing the settings.
Enough about my projects…lets hear about yours. Where do you plan to install the stoker boiler? Do you use a lot of domestic hot water? Why do you say the AHS hand-fired boiler can’t keep up with your oil unit? Would you be willing to fire up the oil boiler to help shoulder the load on exceptionally cold days?
It will depend on the coal you are using to determined what the max btu out put is on any coal burning unit
coal that burns at 13.800 btu per lbs x 20 lbs per hr will be 276k btu per hr input output at 85% efficiency will be 234.600k per hr at 80% efficiency would be 220.800k per hr
At 25 lbs per hr with coal at 13.800 btu per lb will be 345k input out put at 85% 293.250k per hr at 80% output 276k btu per hr
The exhaust temp will be determined by the air setting on blower the higher the air setting the higher the exhaust temp will be be less air setting less exhaust temp .
By controlling the air setting you will control the stack along with a draft control device that is set up proper on the stack pipe
Remember not all Anthracite is the same some needs more air to burn complete other's need less air to burn up completely
and some has more btu per lb then others you got to know the specs of the coal you are using to know what the max btu output will be on any coal burning unit