Harman Mark II Surface Temperature

 
n3hcp
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Post by n3hcp » Tue. Dec. 16, 2008 12:40 pm

I have done searches and have found some reference to the safe surface temperature of a Harman stove, but nothing specific. The instruction manual (yes, I actually read it) says the pipe temp should not exceed 500 degrees, and they recommend thermometers on the pipe and the stove, but never give an upper limit for stove temp. I have e-mailed Harman with this question, but so far no response.

We have a Mark II at our cabin, so it only gets occasional use. This past weekend with an outside temperature of about 30 and burning stove coal, I had 300 degrees on the pipe and 600 degrees on the stove. There is no damper in the pipe. Both are magnetic thermometers, one about a foot above the stove on the pipe, the other is on the front of the stove, above the door on the right, between the door and the warm air outlet vent.

It seemed to he happy at those temperatures, and burned about 50# of coal in just under 24 hours.

So, the question is, how hot can the surface safely be?

Thanks!!!


 
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Post by CapeCoaler » Tue. Dec. 16, 2008 1:23 pm

My MarkII runs between 200-450* F but my thermometer is on the left side even with the top of the glass.
On a 45* day 150-200 will keep the house at 70*
On a 20* day 400* keeps the house at 72*
On a 15*/wind at 40 mph day I hit 450-500* to keep it 72*
You did not mention the sq ft of the cabin.
The 600* stove temp at 30* outside seems a bit high, save the stove coal for the cold days.
Try some Nut coal, it will not get as hot and may cut your stack temps a bit.

 
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jeromemsn
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Post by jeromemsn » Tue. Dec. 16, 2008 1:31 pm

I would place your thermometer on top of the Harman at the center if you can, and get a temp reading there. I run my insert at about 350 it has gone up to 500 once when I left the bottom ash door open and took the dogs out. I won't do that again! I would hate to see how hot one of these stoves can actually get, but I bet it's hot!
With the damper dial on the bottom door it sure does make it easy to control the temps of them though. I run mine about one turn out. Yesterday when the temps went up to 65 here I lost the fire and had to restart this morning when the temps fell back to the 30s.

 
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Post by n3hcp » Tue. Dec. 16, 2008 3:49 pm

CapeCoaler wrote: You did not mention the sq ft of the cabin.
The 600* stove temp at 30* outside seems a bit high, save the stove coal for the cold days.
Try some Nut coal, it will not get as hot and may cut your stack temps a bit.
Yea...forgot to mention...the cabin is only about 800 sq/ft BUT it is open to the roof and there is no insulation in the roof at all! Heat loss is very high. Also has lots of single pane windows. Even at 30 outside, especially with wind, the stove needs to run pretty hard to keep the place comfortable.

It's a former hunting camp and those folks only used it a couple times a year so insulation wasn't a priority. They also had a very large, old wood stove that we had to remove before any insurance company would even think about insuring the cabin.

We just bought it this past spring for a very good price, but it needed a lot of work. Sealing the place up and insulating is on the to-do list, but there were some structural concerns that needed to be taken care of first.

Attachments

Cabin.JPG

The cabin

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Stove.jpg

The stove

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Stove.jpg

The original wood stove

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Post by coaledsweat » Tue. Dec. 16, 2008 5:07 pm

n3hcp wrote:I have e-mailed Harman with this question, but so far no response.
That's odd. :roll:

 
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Post by n3hcp » Tue. Dec. 16, 2008 6:14 pm

coaledsweat wrote:
n3hcp wrote:I have e-mailed Harman with this question, but so far no response.
That's odd. :roll:
I thought so too. It may be because I bought the stove used, albeit from a dealer. I have had experiences with other companies that only respond to original owners. Not saying that's the case here, but... :?:

 
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Post by grizzly2 » Tue. Dec. 16, 2008 6:53 pm

I think coaledsweat is being a bit "tongue-in-cheek" with the "that's odd" comment, notice roll eye happy emoticon. Harman makes a good stove, but by all reports does not provide customer assistance directly. You have to go through a Harman dealer for help. That was a part of my decission to buy a Hitzer. ;)


 
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Cap
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Post by Cap » Tue. Dec. 16, 2008 8:55 pm

n3hcp wrote: We just bought it this past spring for a very good price, but it needed a lot of work. Sealing the place up and insulating is on the to-do list, but there were some structural concerns that needed to be taken care of first.
Great looking little cabin. What county is it in?

Fire the stove at a simmer for best coal usage efficiency and crank it up when you get cold. Not much more to it. If it glows or I should say if you can smell it, your are too hot. Fill & shake every 10hrs. 600F probably a little warm. Spend some time reading here under hand fired section.

 
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Post by Uglysquirrel » Tue. Dec. 16, 2008 9:31 pm

I agree with the last post that 600 stove temp is pushing it.

re: surface temp and where to measure it, to me overfiring is related to the coal temp and the temp of the gasses coming off the fire, so mapped out the Mark II max temperature on the stove top with a IR meter. The gasses pass under this location. The sweet (max hot) spot for any temp stable fire always seems to be 5" rearward of the frt lip same distance left to right.

In my two months of doing coal on the Mark II (newbie) with my install (baro to .06), finding that there pretty much there is a consistent 1.85 ratio between the top temp and stove pipe temp 12" above the outlet (for example some actual readings were 413 stove top, 222 pipe, so 413/222 ~ 1.85)

The book does say 500 deg max at the surface of the chim connector, but let me tell ya, that pretty much suggests that the stove top sweet spot temp may be REALLY high, a lot higher than 600, maybe 700 but I don't have data. If anyone out there is doing a Harman stove pipe connector surface temp of ~500, sure would be interesting to see the stove top temp they are getting.

I agree with the last post, 600 at the stove is pushing it, understand that to get that 10-12 hr shake interval (if you want that ) you need to keep the stove top temp around 350-450. Going to 500 plus stove top you'll really need to add coal every 6-8 hrs, at least that is my experience with Jeddo coal.

Hope this helps.

 
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Post by n3hcp » Tue. Dec. 16, 2008 9:37 pm

Cap wrote: Great looking little cabin. What county is it in?
Bradford County, PA, near New Albany
Cap wrote: Fire the stove at a simmer for best coal usage efficiency and crank it up when you get cold. Not much more to it. If it glows or I should say if you can smell it, your are too hot. Fill & shake every 10hrs. 600F probably a little warm. Spend some time reading here under hand fired section.

That's about what I've been doing. Being the analytical type, I was hoping for a specific temperature above which I should not go. I guess as someone said in another post, burning coal is as much an art as a science.

 
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Post by jeromemsn » Tue. Dec. 16, 2008 11:05 pm

From what I see in your picture of the Harman I would tell you to fill it up with coal. Fill to the top of the fire brick at the rear of the stove and about midway bank it down to the front fire bricks just below the front door. You will get a better burn and only have to shake down every 10 to 12 hours. You should find that one turn of the ash door damper will get you about 350 degrees. after 10 or 12 hours shake fill and bank enjoy.

 
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Post by CapeCoaler » Tue. Dec. 16, 2008 11:22 pm

I hear you about the "camp lifestyle". If you can get some insulation in the ceiling you can hold on to some of the heat and not run the stove as hard.
I do not run the stove any hotter than 500* and the thermo location provides similar temps.
I do not think 600* will do damage if you hit that on occasion but would not feel comfortable doing so all the time.
You really need a bigger stove or a second stove until the camp is tightened up.
MarkIII or a Hitzer Model 82.
The 82 is not pretty but does put out the heat.

 
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Post by n3hcp » Wed. Dec. 17, 2008 12:26 am

CapeCoaler wrote:You really need a bigger stove or a second stove until the camp is tightened up.
Yea, your right. But we got this one for about half what a new one would have cost and it was only a couple years old. Too good to pass up, even if I need to wear my snuggies in colder weather until we can get some insulation in there. :)

 
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Post by coalkirk » Wed. Dec. 17, 2008 7:41 am

That looks nice and peaceful. I see a problem however. Where your stove sits on the hearth you have a brick facade behind it. Behind the brick is a wood framed wall based on the picture of the outside of the cabin. The brick provides no protection from the heat of the stove and that heat transfers to the framing. Everytime that wood gets hot, it's ignition temperature gets lower. you can bet the wood stove was really cracnked when it was a hunting cabin. You need to observe the recommneded clearanaces to combustible surfaces recommended by Harman. That means 24" from the rear and 33" from the side. I'm not trying to be a trouble maker. This is a dangerous instalaltion as is. You can reduce these clearances by half with a properly designed and installed heat sheild.

 
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Post by LsFarm » Wed. Dec. 17, 2008 8:13 am

Hello n3hcp, that cabin looks real nice, a great place to 'get away from it all'.

One item which hasn't been mentioned except by you is a Barometric Damper.. If you install a Baro damper, you will probably drop your indicated chimney temperatures by about 100*. This means that you will be keeping more heat in the stove, and sending less up the chimney to the outdoors. A baro damper will also even out the fluctuations in the draft, making setting your combustion air 'spinner' knob an easier and more consistant job.

Remeber that the magnetic 'stick on' thermometers are just for an indication only, they only indicate the AIR temperature right at the surface, not the real, actual internal temps on the other side of the steel. Usually, on my flue pipe, if the magnetic thermometer says 250*, my probe thermometer, just 3" away but reading the inside temperature indicates 450*+. So if you are indicating 300*, I'd say you actually have 500-600* inside the flue.. You can reduce this considerably by reducing your draft with a baro damper, and save some heat for the cabin.

Is your cabin 'tight' ? That is well caulked and sealed?? If not, you may also want to consider an outside air source for the combustion air to your stove.. If you put in a dedicated 2.5"-3" pipe or line that ends just alongside or under the stove, this duct of pipe will provide most if not all of the make-up air for the air going up the chimney.. Without a dedicated outside air source, this make-up air is coming into the cabin from outside through cracks around windows, doors and floor/wall joints.. These cold drafts make the cabin uncomfortable even when the average temperature in the cabin is fairly warm. Just something to consider.. do a search for outside air on the forum, there are severa threads on the topic..

Hope this helps..

Greg L


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