Dirty chimney?

This is my first year with a coal stove after many years burning wood and frequent chimney cleanings to fight creosote. My stove is a Harman Mark I. I have read that my metal chimney should be cleaned in the Spring so sulfur residues won't combine with moist summer air and dissolve the metal. How about during the burning season? Is a dangerous level of soot likely to collect anywhere, that could cause a chimney fire? How about fly ash? Is there anywhere the ash will collect either in the stove or the chimney and block the flue? My chimney configuration is just a single ninety-degree elbow at the stove and then a straight shot up through stovepipe and chimney.

That's the beauty of coal, there is no flamable afterburn materials, just the fly ash and maybe a bit of dirt/soot. It will mostly collect on horizontal runs of pipe and/or the clean-out of the chimney (if equiped). Yes, it should be cleaned as soon as possible after you shutdown, I believe there is a solution (like baking soda/water?) to neutrilize the ash.

I ran my one stove for almost 3 months and only had 1/4-1/2" of ash in the horizontal run before the chimney.

Replace the 90* at the back of the stove with a Tee and place a cap on the open end with a few screws. The Mark series stoves tend to accumulate ash behind the baffle plate, also in the bottom of the elbow. You can just remove the cap and vacuum it all out, although you will have to use your hand to get the ash out from behind the plate on either side of the vent opening. I usually clean mine about every month or so.

The tee is a great idea. Thanks. Is it really OK to install the barometric damper on the end of the tee, rather than a cap? I am visualizing the momentum of the hot gases carrying small amounts past the vertical and out into the room. There's got to be a lot of turbulence right there where the flue gases change direction.

It works fine but is not the manufacturers recommended location. You will need a manometer or draft gauge to measure the draft since the weight positions will not be accurate in horizontal or vertical in this position.

IMO I would not install the baro in this position unless you have a way to monitor the draft.

I've set the damper up with a manometer, it maintains a steady -.05 " WC. I know a lot of people don't think this position is right for the baro, but it works well, with no leakage into the room. I have found that the chimney drafts a lot more then I thought, the baro stays open at least half way with a full fire burning.

I feel the only way to insure that the draft is set properly is with a manometer, it's just an approximation otherwise, and the manometers are not that costly.

How much does a reasonable manometer cost? Can you recommend a brand and a source?

You should be able to find a Dwyer MkII Model 25 for around $25 to $35 with shipping on ebay. This model is 0 to 3" WC so you will be using it at the lower end of the scale (-.02" to -.06" WC). I have a few Model 40 (measure in 0 to 30 MM instead of inches) for $15 each plus shipping (I bought 9 of them on ebay awhile back). PM me if you want one.

Thanks for the recommendation. So, from looking at the MkII Model 25 on Dwyer's web site, and having watched my furnace guy, I am guessing that I would
(1) Make a small hole in my stove pipe, near the outlet of the stove
(2) Get a bit of copper or other metal tubing that will tolerate flue gas temperatures
(3) Connect the flexible manometer tubing to my metal tubing
(4) Level the manometer and zero-adjust the fluid
(5) Shove my copper tubing into the stove pipe hole, to the center of the pipe, and take a reading
(6) Adjust the barometric damper weight
(7) Take additional readings and continue to adjust the baro unti I get the .06 called for by Harman
All the above while the stove is operating "normally" at a steady state.

Does the manometer come with its own metal probe, or do I have to make something heat-tolerant as described above? And if I do make my own probe, is the inside diameter of the tubing critical or not? (I DID pay attention in high school physics, but it's been a long time....)

The manometer doesn't come with a piece of metal tubing. The probe can be a piece of brake line or any other metal tubing that will fit the tube on the manometer. Once you have the piece of metal tubing then you drill the hole, it needs to be snug so as to measure the negative pressure. Only has to be inserted far enough to measure the draft, it is not measuring velocity.

Have fun.

The Dwyer Model 25 comes with the fittings to bolt into the flue pipe. Just buy a length of brake line & you are all set. Don't even use the supplied tubing. You will only be using one side of the manometer.