Burning up grates on my Harmon stoker

I am in my third year of using my Harmon Magnum Stoker. I am told by the dealer and by the Harmon rep that I should not need to replace the cast iron burner grates more than once every few years. In my case however, I need to replace the grates about 3 times a year. The grates warp and get pitted and then don't sit properly. This hinders the coal flowing properly across the grates. Sometimes the coal backs up and flows off the sides of the grate holder, or even picks up the grates and eventually snuffs out the fire. I burn 6-7 tons a year and have got coal from 3 different sources. I am told by Harmon that I am the only one that has had a problem like this.
The stove is in the basement. I have a barometric damper just above the stove on the vertical pipe. The pipe then goes horizontal on about a 20* angle for about 4 feet. It then goes verticle into an 8" masonry chimney and goes up two stories. The dealer rep thought maybe I had too much draft and suggested I install a manual damper above the barametric damper to try to slow down the draft. This did not seem to have any effect on the grate issue.

Obviously, I can just replace the grates, but this will get expensive. Any ideas???

Have you ever checked the draft with a manometer to find out what it actually is? If there is too much draft the baro will be to it's limit, the fix is not installing a manual damper but installing a larger baro damper. Either way it's a moot point if you don't have an actual reading of the draft.

Hi Jerry, welcome!

If you are having those kind of troubles it sounds like too much combustion air. Does your stove have a metal flap over the air inlet on the combustion fan. If so you need to cover the inlet half way or so until the flames are nice and blue. If they are yellow that could mean too much air. The best way to set it up is with a draft gauge measuring the stove pressure, but you can get it close by starting at half covered and moving it small increments to get a nice flame.

On the subject of draft, as John said you need to actually measure it but absent of that make sure you have the damper hinge pins level and set the weight on .04 per the directions. That should be close enough not to have the kind of problems you are having..

Keep us posted and maybe post a pic of your flame size and color.

7 ton of coal on 85,000 BTU unit is quite a bit, others that have them could confirm but most of the people I've dealt with that had smaller units like that usually used about 4, maybe 5 tons at the most in year. In other words I would suggest you're possibly working it to death with it continually being fired.

Oops, sorry, forgot to say Welcome, Jerry.

Thanks, Matt and Richard for your posts as well. You guys know stokers better than me (for now...)

Richard S. wrote:7 ton of coal on 85,000 BTU unit is quite a bit, others that have them could confirm but most of the people I've dealt with that had smaller units like that usually used about 4, maybe 5 tons at the most in year. In other words I would suggest you're possibly working it to death with it continually being fired.

I agree with Richard that the coal usage is over the average forum member; however, the stove is designed for 85,000 btus continuous output. If you divide that by average coal heat content (~ 13,000 btus per #) and multiply by 24 hours per day and then again by 30 days average per month, you can burn 2.4 tons per month at full output. So if the stove is working that hard on a regular basis then I could see a set of grates per two years or even 1.5 but three sets per year seems excessive.

Jerry if you give us some more data on exactly how much coal you burn per average month and if you know it the amount of coal burned per set of grates. Also how much area you are heating and what the stove temps are above the front door, how much fire is on the grate on average, and also the stack temp, that will give a little more info to compare your usage with mine.

I purchased a 10 year old Harman last year that was in service for over 7 year and burned more than 35 tons of coal before the owner had to replace the grates, and even then it was only one side that had gone bad..... so in short even based on your enthusiastic burn levels three sets per year is too much.

Definitely agree its too many even if it is being over fired, on the other hand my car can go 120 MPH but its not going to last that long continuously going that fast. Possibly the combination of extensive use and some other issue.

As Matthaus mentioned need more info, settings you have , temps etc. The more you can provide the better, even if it seems inconsequential to you.

welcome to the forum.

The only thing I can add is that this is my 3rd season running my Magnum Stoker (bought new) and I've never warped or damaged a grate.

You have too much draft or your plates are not sealed and the air is not going directly thru the holes it might be blowing around the edges or too much combustion air as others have stated. Something needs adjusted....

I have 2 stoves (Keystoker & LL) that are 3-5 years old and have never replaced the grates.

Thanks everyone for your response. I will try to address some of the questions that were posted. My house is a 2600 sq. ft. two story with an oil fired hot water baseboard central heat system. I keep the thermostats at about 65 and until the outside temp gets into the low 20's the oil system does not run. By the time the outside temp hits the low 30's the stoker is running flat out and does not cycle off. I have small coal bin outside that feeds through a 4' pvc pipe into the hopper, so I don't know how much I burn on a daily basis. I just loaded it manually and will get a 24 hr burn amount by tommorrow afternoon.

As far as the draft... with the set up I have been using my draft in the stove is at .04. That is with the manual damper mostly closed, the vent on the blower motor at half, and my barometric damper weight at .04. If I close the vent on my blower motor full closed, and open up the manual damper to full open (no restriction) my draft meter still shows .05. I was told by the dealer rep, that I may have too much draw from the chimney and that is why I was told to restrcit my draft with the manual damper. With the barometric damper set at .04 and no restriction set on the manual damper, the baraometric damper is wide open. Using various settings on the stove and chimney, I can vary the draft from + .02 to -.06. As far as the grates, I have tried cementing them in so there is no air going anywhere except the holes, and I have tried just laying them in as the manufactorer sugests. The best I could do with my tools for a chinmey temp. was to stick an oven thermometer in through the barometric damper to the chimney. The temp showed 400*. I will try to attach a picture of the flame... thanks again for the advise...

Jerry

Based on the nice blue flames your combustion air is about right. Based on the high flue temp I would say the too much draft scenario is the best bet to try and solve. it sounds like your 6" barometric damper will not let enough air in for the size of the chimney so you are still getting too much flow. The manual damper would seem to be the right way to slow it down, but actually IMO the restriction is speeding the air up and making the situation worse. Since you are running on the upper end of the stove capacity, perhaps an 8" flue with baro would help the situation and be more able to handle the heat while allowing the stove to breath.

Just my $.02.

Hi Jerry

I'm a big skeptic so dont be offended by the IFs.

Take a look at the attached page from the manual the grate system is simple and the best way to fix a problem is to start at point A and examine and recheck the important variable's. If your draft readings are correct as stated I would think that eliminates that but when where these readings last checked and verified

Do it again if not within the last few days just to be certain and if there is any uncertainty about what you are doing get some help with it . To most it would appear to be the most likely cause of the problem.

If all that checks good I would remove the large cast iron grate holder and inspect for warping or some other defect that is preventing the grate plates from fitting correctly and laying flat all around the edges of the plates, also check that the the gasket underneath is in place and sealing. Was the bolt retaining the grate holder in and tightened ?

Since this is not a usual problem we got to look at the odd stuff I'm wondering if while there is enough airflow coupled with a strong draft to support good combustion but that the volume of air being moved by the combustion fan up thru is not enough to create a slight cooling effect to the underside of the grate plates . Also if the grate holder passes a visual inspection I would head to my Dealer for a side by side comparison of a new one .

Its a simple system and something is not right so start at point A and eliminate the possibilities

thanks again for the responses. the draft readings were taken today. I have new grates on order and when they come, I will disassemble the grate holder and check the gasket. I will let you know...

What exactly is the purpose for the barometric damper. does it control the draft inside the stove, or cool down the chimney with ambiant air???

jerry

jerry wrote:does it control the draft inside the stove, or cool down the chimney with ambiant air???

It controls the draft leaving the appliance, it does this by breaking the chimney's draft on it. It allows room air to replace what you don't want leaving the coal burning unit to satisfy the chimneys pull.

jerry wrote: I have new grates on order and when they come, I will disassemble the grate holder and check the gasket. I will let you know...

jerry

jerry I see you have a digital camera and know how to post pics,
Please take a photo of the warped grates before removing from the holder and also a nice detail pic once they are removed perhaps there is a clue here to found, I'm anxious to see'em