New Harman SF-250

New Harman SF-250

PostBy: Cap On: Mon Dec 26, 2005 9:50 pm

Hello Folks--

I purchased a new Harman SF-250 last week. This is an upgrade to the Harman Mark III I've been using for the last 3 winters. So far I 've found the SF-250 to be slightly more difficut to use but I am sure I will learn it's operating characterisics soon. It produces much more heat as it should. The firebox is huge! I am debating on whether I should purchase and install the heat accumulator and run stove pipe to a grate through the basement ceiling. I may have too much heat in the living area :!:
The Mark III was slightly undersized to heat my entire home. I do not suspect I will have similar problems with this new unit.

While the Mark III has the classic look of a high quality coal stove, the SF-250 has more of the furnace look to it. But one can see the quality built into this unit. She is big & heavy. Now if only the temps wall fall back into the teens, I could really put her to the test :!:

I'll post an image of the 250 soon. I also have the Mark III for sale. Intersted persons may locate it listed under the NEPA Index for appliances & stoves for sale. An image of the Mark III is also shown under the *pictures of your stove* thread. I have cleaned it up. It's actually looks much better now.
Hand Fed Coal Boiler: Harman SF 250, domestic hot water loop, heat accumulator

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SF 250

PostBy: MILLERTIME On: Wed Dec 28, 2005 9:41 pm

Stove/Furnace Make: Harmon
Stove/Furnace Model: Harmon sf250

PostBy: AL-53 On: Wed Dec 28, 2005 9:54 pm

The SF250 is a beauty....I was going to get that..but I think I would of melted the house...i got the Magnun Stoker instead....and that is plenty ..with heat to spare....


PostBy: Cap On: Wed Dec 28, 2005 10:29 pm

Thanks Mr Miller. It's been quite balmy since I installed the 250 last w/e. But I do have a few questions.

Is it possible to burn a handfired unit such as this 250 less than full burn? At what point is there too little draft? And do you have any clever ways of building less than a full firebox of burning coal? In order to run less heat?
( I always wondered if laying a flat steel plate covering a portion of the firebox would work ).

I suppose trial & error will answer my questions over the next few months but any help would be appreciated.
Hand Fed Coal Boiler: Harman SF 250, domestic hot water loop, heat accumulator

PostBy: lime4x4 On: Wed Dec 28, 2005 11:48 pm

yeah I hate this weather myself..Wish it would stay cold but atleast it makes the coal last
Hey Cap I sent u a pm the other day

PostBy: Cap On: Mon Jan 02, 2006 8:34 pm

Hello List!

I've been using the new SF-250 since 12/24 and it has been working great! I couple of notes:
- With a good fire cooking, my flue temperature is 140 F. & my warm air off of the blower is 160F! Are all coal stoves this darn efficent?
- Harman sells two options for this unit.
a.) A firebox reducer
b. ) A heat collector.

I am intersted in both but I am not sure I need to throw out money for something I can create myself, such as with the firbox reducer. I gathered up some my old and busted up firebrick from the garden and piled it into the front area 10" deep into the firebox to see if this would allow me to run a smaller fire. ( The SF-250 has a deep box ) I've tested this idea and so far it has worked good. I understand the Harman kit includes some brick and a metal plate to build a wall? I haven't seen the kit.

I do want to purchase the heat collector. This will allow me to run duct directly to a register in the floor. Okay, here is my question...

How many feet of 6" duct can I run? I would like to purchase some insulated flexible duct and run it 30 ft across the basement ceiling? Can I push the warm air this far? The unit has a 135 cfm blower.
Hand Fed Coal Boiler: Harman SF 250, domestic hot water loop, heat accumulator

PostBy: lime4x4 On: Mon Jan 02, 2006 9:04 pm

insulted plastic duct probably won't last long.I know when I was running mine thru a metal duct that was insulated I was cing temps of 400 to 500 degrees at the floor register.The magnum stoker can handle 1 floor register up to 20 feet away.Yours is probably the same since both use the same blower motor size

PostBy: Cap On: Mon Jan 02, 2006 9:24 pm


The duct I am looking at is rated for 250 F. I can purchase it in Allentown at a commercial ac/heating supply house. I do not believe it is plastic.
Hand Fed Coal Boiler: Harman SF 250, domestic hot water loop, heat accumulator

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PostBy: lime4x4 On: Mon Jan 02, 2006 9:55 pm

based on mine your gonna excede 250 degrees esp by the stove.I ran my duct 10 feet and it was super hot at the register.I used 6 inch galvanized stove pipe and used that insulation with foil wrap designed to fit over the pipe

PostBy: Cap On: Mon Jan 02, 2006 10:17 pm


I am seeing warm air temps of 160F coming off of the blower. I am not overfiring my stove. I have seen the flue temps peg my 220F thermometer, but this only occurs one the ash pan door is open. I cannot see how it is possible to push 400-500F warm air off of my stove into duct . And I would defintely use black stove pipe for the first 6' to 10' before the transistion to the flex duct.

If you are seeing temps 400-500F , what are you doing to allow the temps to get so hot? Is it safe?
Hand Fed Coal Boiler: Harman SF 250, domestic hot water loop, heat accumulator

PostBy: lime4x4 On: Mon Jan 02, 2006 10:42 pm

i'm not over firing the stove.the stove body is around 500 degrees.Maybe it's just the way it's designed.I know u can't hold your hand 5 inches in front of the vent off the stove when it's burning at max feed rate.Your's might be design differently so that it doesn't get that hot

PostBy: lime4x4 On: Mon Jan 02, 2006 11:29 pm

okay just checked again.I'm no longer using the vent option since I moved the stove to the first floor.When it's on max burn the steele just below the vent opening is reading 500 to 550.When the stove shuts off and goes into pilot mode and then the blower shuts off the temp shoots up to almost 750 degrees. I hope that helps

Re: New Harman SF-250

PostBy: neilthewheel On: Sat Jan 03, 2009 1:03 pm

Did I read correctly that you were going to sell your Mark III ? If so I am Interested.
Stove/Furnace Make: Vermont
Stove/Furnace Model: Vigilant

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