Harman SF250 Tech Info Interesting Stuff

this deserves its own thread

I called Harman today to inquire about their SF250. the tech who took the call happens to own one. His Dad bought it in 1990 and handed it down to him. he said the stove is "generational" and built like a tank, meaning it can be handed down for a long time to descendants, that's how sturdy its built. in the past 23 years all he did was re-brick it once a few years ago. it burns in a 3000 square foot basement and keeps it 80 degrees. he fires it with the main ash door draft knob open 1/2 its total travel ! thats a lot of main draft.

anyway the reason I called was this- why does an SF250 have TWO fire door draft knobs, but only ONE ash pan draft knob ? one of the few stoves ever built that way. he didnt know. I told him, ask an engineer. he said ok and put me on hold. he got back in 1 minute, and said this:

the SF250 was originally designed as a dual fuel stove, wood or coal. the bottom draft knob was for coal, the 2 top draft knobs were for wood. wood burns from top down. coal from bottom up. he said he NEVER uses the above fire draft knobs in his SF250, ever, and for all he cared they could be welded shut closed. he runs the fire door knobs closed and burns coal using the bottom ash door draft control. he also said SF250 has fixed window vents in it, for secondary air, so the fire door draft knobs are redundant for coal.

the SF250 was designed in 1980's. since then EPA has outlawed it for burning wood, it can be sold legally as a coal burner only. the fire door draft knobs remain as a throwback to when it was a wood burner too, they just never changed the design, and left them there. for now.

I bet he walked into another room and asked Dane Harman, the founder and original designer.

Dane may not own the company anymore, but he is still around when needed.

Rusty-
Thanks for the info. I've heard different things about how to use those 2 load door knobs. My stove dealer (who runs a sf 260 boiler) said to open them more as you open your ash door knob. He said it will allow you to use less coal to run some air over the fire. I know some people on the discussion boards said to keep them closed because they are for burning wood. I'm still learning the ins and outs of my stove after 4 years of running it.

Enjoy the heat it puts out.

thanks for reply. it comes down to how critical is above fire airflow in a coal stove. what they did was made the glass wash air fixed slits so no matter where the fire door knobs are set, a wood fire will still burn using the glass door slits, and a coal fire will still have enough above fire air to burn off the byproducts in the heat exchanger. it takes a lot of guesswork out of it for the average operator. those stoves will burn a full load of wood overnight, with the bottom ash door draft closed completely, just using the fire door window slits as combustion air. but the smoldering fire will create a lot of creosote. the top door vents would be adjusted with a wood fire to maintain a minimum 250 F stack temp eliminating creosote buildup. if bituminous coal was used, the fire door draft controls would come into play as a major adjustment to extract the most BTU's from the bit gases. that is very flexible capable stove.