Coal Burn Rate 4 vs. 6 teeth

Curious to know the difference between running my efm df520 at 4 teeth and corresponding air setting vs. 6 teeth and a higher air setting to achieve a proper fire. At 6 teeth you use 50% more coal as 4 if the run time is constant. With a higher feed rate, the fire should heat the water faster. The question is, which is more efficient? I realize that under controlled conditions, statistics could be collected to prove this one way or the other but controlled conditions are only available in a lab. Any thoughts?

Ideally, you'd only want enough feed to make enough heat to warm the required radiation. Short cycling isn't as good as long cycles. If your required heating needs cause the stoker to run for moderate periods of time, I would leave the setting as it is. If it heats up rapidly, you're eventually run into the high limit shutdown problems in warmer weather. You should keep a 40 or even 50 degree spread between the high and low limit on your aquastat.

The standard advice is to find out a good feed rate and leave it there all year round. 5 teeth is a pretty common setting; some can get by at 4 teeth. I very seldom hear about people higher than 5, but I'm sure they are out there.

Our salesman, with about 40 years in the service of stokers (and oil) says he never checks for efficiency. You feed coal as your general needs require, look for a good ash ring, keep it clean and lubed, and forget about it.

Your best bet is to start at a low teeth setting and increase one tooth at a time until your needs are met. Then, you may be able to stay at that setting all year long.

In my experience during the heating season it works out to be the same coal usage, whether (exaggeration) running 60 minutes per hour at 2 teeth or 10 minutes per hour at 10 teeth the amount of coal burned is the same. You have to burn so much coal to produce the BTU's your house requires, like stoker-man says set it so it doesn't short cycle or run constantly. In the summer a lower feed will use less coal, simply because the timer is running the stoker 5 minutes per hour to keep it lit and most of that heat is just wasted. I use the lowest feed that will supply a hot shower while also running the washing machine and dishwasher, it is 3 teeth for me. 99% of the time the stoker feeds off the timer in the summer, I could probably use 1 or 2 teeth but I saw the burned pipe pictures so I don't. I have a big house and I have mine at 5 teeth feed and 4.5 air. On very cold days (below 10 degrees prolonged temps) it runs quite a bit but always keeps up with more than enough heat, on average winter days in the 20's it has a good rhythm. I think if we get a cold snap with a week of -10 or colder I might have to increase the feed.

If it heats up rapidly, you're eventually run into the high limit shutdown problems in warmer weather.

To elaborate: In the warmer months, your 6 tooth setting may result in a rapid production of hot water and an override of 50 degrees when the stoker shuts off. If you don't use some of that hot water in the next half hour, the timer will call for 2 1/2 minutes of run time to prevent an outfire and the timer won't operate the stoker because it's shut down on high limit. You will start experiencing outfires.

Stoker-man, have you experienced problems with outfires personally? I know what the manual says, but I had my boiler shut off for about 6 hours in the summer (I forgot to turn it back on after adjusting the feed) and the fire didn't go out. The natural draft kept it lit, I mean it looked out but as soon as I turned the stoker on it came right back to life.

No, I have a hand-fired boiler, but I would have to say that it is the number one question I get at work from the public.