Coalpail.com Forum

You are right, 170-180 degree water is what you would expect. I can only assume that the system wasn't properly designed. This boiler's water is fed to the cast iron radiators in the house by gravity, no pumps or zone valves. The supply and return headers are 2 1/2" and the piping to the radiators are 1".

I don't know how I could hold the water in the boiler to run it up to 170 since 107 held the house at around 72 degrees F for an entire day of 8.6 degree outside temp. If I took it up to 170, I'd have to open all the doors and windows and I'm sure it would still be hot in the house.

There is a pump on the oil boiler that is piped in parallel with the coal boiler but I have the same issue when it operates, no matter how high I set the oil boiler once the pump starts and the cooler return water enters the boiler, the temperature quickly settles in between 100 and 115 degrees F depending on the outside temp. Not good temps for an oil fired boiler. The oil boiler only holds about 6 gallons of water at operating temperature while the pipes and radiators in the system hold a couple of hundred gallons.

This is the basic layout of my system except that I have 13 cast iron radiators and there are 2 supply and 2 return headers, one set feeds one half of the house while the second set feed the other side of the house.
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You make some good points on "your" style system.
Maybe some old veteran hydronics system guys could comment on this.???

Just some general comments........ Many years ago we lived in a house in SW PA that had a similar system. Big hand fired boiler and similar gravity hot water system. We also burned bituminous coal. I would say this was about 1950 to 1955 era. We did not think much about whether it was good to run the boiler at any particular temperature - we just ran it hot enough to keep the house warm. And I mean WARM -- it was not unusual for it to get up to 80 in the middle of the winter, just because of the reasons you are talking about. Generally we were able to maintain the temp in the low to mid seventies but with coal at $5 a ton in the bin - being too warm never seemed like such a problem.

Anyway - a few comments you are probably already aware of. You want to maintain a good draft in the flue. We did use a manual damper but no barometric (not even sure I ever heard of one until much later in life). The manual damper was generally run wide open during the day and we controlled the fire level and boiler temp by balancing the vents above and below the fire bed. At night when we were banking the fire before going to bed the damper was closed a bit to better hold the fire all nite..

The control of the boiler temp was done by which vents were open. If the ash door vent was open, the air was drawn through the coal bed and caused the bed to get hotter. If the vent in the front door was open the air was drawn in the front door and across the top of the bed of coal to ignite the volatiles. The balance of the stack damper and the ash door vent and the front door vent allowed you to set the fire to yield a pretty broad range of boiler temps. Generally both vents were partially open to keep the bed alive but also to provide combustion air for the volatiles.

It was easy to get it hot - open the stack damper wide and the ash vent wide, shake it, and let 'er go. Got really hot - the trick was to only do that long enough to get things heading in the right direction and then to begin cutting things back to anticipate the boiler temp increase. Remember this is mostly art, and little science --- the theory is sound but every boiler and installation is a little different. - It does not take long to get the feel of things - just remember - the thermal inertia of the system will make everything take a while. As others have said - adjust and wait - you will get the hang of it. - and then its fun (at least I think it is) - kind of primal!

Oh - and as said by others above open the draft and get the bed hot before shaking - and be careful when tossing a shovel full of bit onto a hot fire (especially if its got lots of fines or a lot of volatiles). Be certain the stack has a lot of draft when you put the coal in and better to toss in a few partial shovelfuls than on huge one. I singed my eyebrows more than once by being in a hurry and tossing in a mighty load only to quickly generate more volatiles than the stack could carry away so kapuff - out the front door comes a face full of hot stuff - you learn real quick - DON'T to do that

I think I'm getting the hang of setting the dampers. I quickly learned the importance of the over fire draft with bit coal. Oddly if I open the over fire damper when burning wood the stack temp drops and the fire dies. Not what I expected.

I monitor the stack temp with a wireless thermometer. With the baro damper in play, I can set a stack temp and it pretty much stays constant for hours. When it starts to drop It's time to add coal. Wood is far more cyclic and needs more feeding and tending than the coal does.

I wish I could get rid of the puff back into the basement when I open the door and like you said, especially when adding fresh coal. I have plenty of draft, my chimney is 29 feet tall. I bring the fire up and open the manual pipe damper before opening the door which helps the draft. I have reduced the shovel size but puff back is still an issue that I would like to solve. I get puff back when burning wood to but to a far lesser extent.

I put one of those magnetic thermometers on the stove pipe. It would fall off when the pipe got hot so I screwed it in place. It was a waste of money. It is only somewhat accurate when the pipe is clean. As soon as the pipe starts to soot up it reads as much as 100 degrees lower than the thermometer I have stuck in the pipe.

The nice thing about the low water temps when burning wood is that I get no creosote in the chimney. It forms on the walls of the fire box and flakes off and burns.

The puff backs might be due to the coal itself.

For about 6 years I used a highly volatile coal(I called it match light), and I couldn't stop puffbacks.
I lost arm and face hair several times. As I posted in another thread, my last puffback with that coal blew flames completely around my waist.

The coal I'm using now only puffs back a little smoke if I don't open the mpd completely.

The difference in heat between the 2 coals is amazing also. The highly volatile coal would turn the stove cherry red, but little heat in the house during cold weather, the coal I'm using now throws bunches of heat into the house without overfiring the furnace. I'm actually running it like the Anthracite guys here are doing. Just fill it to the top of the firebricks, leaving an open area in front and let it go...............I even get blue ladies

Unfortunately we don't have a great selection of coal here anymore since the mines closed. I bought what I'm burning two years ago. I think the coal dug from seams near the surface. It's not screened and is everything from fist sized lumps to dust, rocks and mud. Right after I bought it the grates broke and I just found a set this fall. The previous owners obviously didn't keep the ash pit cleaned out, the original grates were warped and cracked. I had already bought wood and planned on installing a steel plate to burn wood in the boiler.

I covered the front grate with fire brick today and the wood is burning better and I seem to be getting very little wood smoke out the door now.

I found some tables that list the max BTU that can be connected using different stove pipes and chimney liners and sizes.
http://inspectapedia.com/chimneys/Chimney_Flue_Size.htm#C9F

I found a formula in another thread that estimates the BTU input based on firebox dimensions.
Need Internal Length and Width Dimensions for Your Firebox

My boiler's estimated BTU capacity of 141,750 BTU exceeds what the 6" pipe can handle, something less than 124,000 btu, according to the table, since the pipe has no rise, it goes straight into the chimney. The chimney liner is 6" square and can handle a total of something less than 195,000 BTU because a square liner develops less draft than a round liner. My oil boiler is 105,250 BTU so I could never run both boilers at the same time, not that I would want to but the chimney couldn't handle it.

If I reduce the firebox length dimension by the width of a fire brick the estimated BTU becomes 111,375 btu, pretty close to my oil boiler and within the capability of the stove pipe. I wonder if with coal it would be enough to just cover the grate to reduce the open area or if it would have to be filled in to the top of the fire box?

imaddicted2u wrote:If I reduce the firebox length dimension by the width of a fire brick the estimated BTU becomes 111,375 btu, pretty close to my oil boiler and within the capability of the stove pipe. I wonder if with coal it would be enough to just cover the grate to reduce the open area or if it would have to be filled in to the top of the fire box?

They did what you are describing in this thread: Successfully Burning Anthracite Coal in a Clayton Furnace

I learned a lot just from that thread alone. Even though it's about Anthracite , the basics still apply..........just need to tweek a little with Bituminous.

You've done your homework...Now you need to start testing to see what works best with this unique installation.

Some other thought's I have...
Have you tried running this boiler with the oil furnace flue pipe disconnected and capped (with baro still in place)? I'm wondering if the oil unit could be stealing enough draft to be causing puffbacks when tending the coal boiler...?

Have you tried running the boiler without the baro and just using the stove pipe turn damper to see how it performs?

Also, basements can have lower air pressure caused by 'stack effect' of the house that can affect the chimney draft. Opening a basement window while tending the boiler is an easy way to determine if that's causing the smoke puff back issue.

SWPaDon wrote:

imaddicted2u wrote:If I reduce the firebox length dimension by the width of a fire brick the estimated BTU becomes 111,375 btu, pretty close to my oil boiler and within the capability of the stove pipe. I wonder if with coal it would be enough to just cover the grate to reduce the open area or if it would have to be filled in to the top of the fire box?

They did what you are describing in this thread: Successfully Burning Anthracite Coal in a Clayton Furnace

I learned a lot just from that thread alone. Even though it's about Anthracite , the basics still apply..........just need to tweek a little with Bituminous.

Thanks, I'll give it a read.

rockwood wrote:You've done your homework...Now you need to start testing to see what works best with this unique installation.

Some other thought's I have...
Have you tried running this boiler with the oil furnace flue pipe disconnected and capped (with baro still in place)? I'm wondering if the oil unit could be stealing enough draft to be causing puffbacks when tending the coal boiler...?

Have you tried running the boiler without the baro and just using the stove pipe turn damper to see how it performs?

Also, basements can have lower air pressure caused by 'stack effect' of the house that can affect the chimney draft. Opening a basement window while tending the boiler is an easy way to determine if that's causing the smoke puff back issue.

Hmm, I've run with the oil boiler disconnected and its chimney inlet blocked so the coal boiler owned the flue, no baro, just the manual damper. I've run with the oil boiler piping connected and the baro blocked. I haven't tried with the oil disconnected from the baro and blocked. It's worth a try. To date the best performance has been with the baro and the manual dampers used together. The baro smooths out the draft fluctuations and as I close the MPD I can see the boiler water temp begin to rise within minutes.

"Puff back" may not describe well enough the amount of smoke I get out the door, especially when adding coal.

Yep, opened the basement door many times, made no difference. As a matter of fact puff back must have been an issue long before I got here...lol. The previous homeowner had a bathroom fan above the front of the boiler with a flexible dryer vent that ran across the ceiling and ended up above the basement door. It was full of soot.

I haven't burned coal since I sealed the heat exchanger door leak. So I may see an improvement. I'm burning wood right now and another thing I did was block off the front grate with fire brick. I have to say that the wood is burning better and with noticeably less puff back when the door is opened. I think I leave the grate blocked next time I burn coal and see what happens.

Oh, so the smoke rolls out when the door is open...Then I believe you're right, the 6" flue is simply too small for the firebox.

If reducing the size of the firebox doesn't help much, a draft inducer might...You could just use it when tending the fire and leave it off the rest of the time. The baro damper would have to be covered/capped each time though.

Not sure how your oil furnace is built but the oil furnace is probably letting air into you chimney, thou the blower, into the combustion chamber and up the stack.
I would be interested in stopping all extra unheated air up your undersized flue. I like the Barometric damper.

Short Bus wrote:Not sure how your oil furnace is built but the oil furnace is probably letting air into you chimney, thou the blower, into the combustion chamber and up the stack.
I would be interested in stopping all extra unheated air up your undersized flue. I like the Barometric damper.

There is a good explanation of the air shutter in my oil burner at 2:06 minutes into this video, oil pressure opens the shutter, no oil pressure and the shutter closes blocking air from entering through the blower.
https://www.youtube.com/watch?v=09-w2PG9DRI

rockwood wrote:Oh, so the smoke rolls out when the door is open...Then I believe you're right, the 6" flue is simply too small for the firebox.

If reducing the size of the firebox doesn't help much, a draft inducer might...You could just use it when tending the fire and leave it off the rest of the time. The baro damper would have to be covered/capped each time though.

I believe the chimney is capable but issue is with the stove pipe to chimney installation. A 6" stove pipe on a 30 foor chimney, mine is 29 feet, with a 3 foot rise can support 160,000 btu, 2 foot rise can support 142,000 BTU and a 1 foot rise can support 124,000 btu. Since my stove pipe is installed horizontally it can handle something less than 125k btu. I haven't been able to find anything on the rated boiler capacity. The original boiler design had a 9" smoke pipe.

Here are a couple of pics of the draft gauge taken this morning with NO fire burning. Outside temp is 43 deg F. Wind 16 MPH. I haven't had a fire on since last evening and it is still 71 deg F in the house.
Baro clamped shut and MPD open:
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a six inch pipe is too small - you need flue area to handle the gasses and smoke when the loading door is open, not height or draft. I like to recommend 8" min. when burning bituminous coal. bigger is better. don't be afraid of a little soot, brush out the heat exchanger from time to time, but don't loose sleep trying to keep it clean constantly. the mpd's a soot catcher, and I'd bet that your connecting pipe is probably full. I don't like the idea of mixing wood w/ bit coal - it soaks the powdery soot (which isn't really a chimney fire danger or all that flammable) with creosote and creates a fluffy, crusty mix of flammable junk; it also prevents the soft fragile bituminous soot from being easily brushed down. Use lots of T's for easy cleanout on the connecting pipes. Post your location or check the bituminous coal sources thread to find a better source of coal, your coal sizes are too small, you need lump.