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Outdoor boiler (revisited)

Started by Engineer, October 15, 2006, 08:49:47 PM

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Engineer

Question for you outdoor boiler users - specifically the Central Boiler or others using an open system.  The past couple days it's been in the 30's at night and 50's during the day, and I've been running the boiler with a very light demand keeping heat in the new house while we tape, mud and paint.  The only heat in the entire, three-story place is the radiant tubing in the basement floor slab.  When the thermostat is set at 66, the entire house is toasty warm and the floor is warm.

Problem is - that light demand, coupled with a hot fire, has made my boiler overheat and release considerable steam and hot water out of the top vent.  Yesterday it was seriously overheated and water running in streams off the roof, this morning it was just a few wisps of steam. The water temperature both days was 211 degrees....  What's causing this and is it normal?  I was able to "calm it down" both days by opening up the house and cranking the thermostat way up to introduce some cooler water into circulation.  I can't imagine this happening in midwinter on a high-demand day, but the fact that it's happening at all has me concerned.  Not so much for the unit, but that the circulator pump could be affected by steam.

On a completely unrelated topic, I'd also like to know what kinds of "tools" and implements and accessories you are all using to make it easier to maintain and operate your boiler.  Right now, all I have is a scrap of lath, 6' long, that I use as a "poking stick" to keep the wood piled up and coals stirred around.  Every time I use it, it tries to burn up.   :D

wiam

Jon, it is very rare for my CB to overheat. I have the CL40.  Mine runs all summer to heat domestic and waterbeds, so not much load.  I wonder if you might have a door gasket problem. 

I got the package from CB when I got mine.  There is a flat blade shovel with wood handle.  I use this for cleaning out ashes.  (when it finishes burning off I think it will get a steel handle)  There is also what looks like a long handled hoe with a hook on the back.  That still hangs in the shed.  The other tool looks like a long handled potato hook.  These both have steel handles.  I use the latter for poking in the fire.  My favorite for poking is a piece of 1" galvanized coduit about 6' long.  My plan is to weld a small tab on the end to pull wood back to me when moving stuff in the fire. (have planned on doing this for about a year)   If you use a pipe, be aware that some coals will come out of the fire inside the pipe.

Will

Corley5

Sounds like you you've got an air leak somewhere. 
Burnt Gunpowder is the Smell Of Freedom

chet

As Corley said, you either have an air leak (most likely da door seal) or a faulty aqua stat. Call CB  ;)
I am a true TREE HUGGER, if I didnt I would fall out!  chet the RETIRED arborist

beenthere

I agree with the air leak (or like Chet says).
Do you know how it shuts itself down, to keep from getting the water temp over about 200° F ?  Large mass being heated is harder to shut down, as there are hot coals that will cause water temp to continue to rise, when the damper is closed (I assume you have control over inlet combustion air).

I have a damper that closes when water temp reaches about 185°, and if there is a real hot fire with a full charge of wood, then the temp will rise another15°.  But when I know the demand is not there, I don't fill it with wood, but control the amount of fuel load from experience to satisfy the heat demand. May not be so easy with a large outdoor boiler.
It's not normal, IMO, but is exceeding the safety release valve setting if blowing off hot water (doubt it is steam, but is steamy :)).

south central Wisconsin
It may be that my sole purpose in life is simply to serve as a warning to others

Engineer

There's a damper in the door which is electrically activated.  I have the thermostat set at 185 degrees, which means the damper opens at 175 degrees and shuts off once the water temp reaches 185.  I have checked the damper and it's operating fine, both in terms of when it opens and shuts, and HOW it opens and shuts.  I've also checked the door gasket and it seems to be OK as well.  The boiler is virtually new.  I had it operating in March and April for a total of about ten days, and then fired it back up three weeks ago, where it's been run intermittently.  The last three days and nights have been cold enough to fire it up pretty much continuously.

Any chance that a raging hot fire and residual heat, coupled with low heat demand, could jack that temperature up to the boiling point?

BBTom

I like to use wood that is not very dry for those low demand days.  Dry wood will have a tendency to do just as you experienced.  Some green wood in there will help kill the heat and just smolder when the damper/fan shut down.
2001 LT40HDD42RA with lubemizer, debarker, laser, accuset. Retired, but building a new shop and home in Missouri.

Dana

I still think the door damper isn't working correctly. It is possible it looks closed but is hanging up. I know on mine, you can't see all of the damper due to the smoke shield in front of it.
Grass-fed beef farmer, part time sawyer

Engineer

I'm goin to see what it does today - another relatively dry sunny day in the 50's, it was 34 last night.  I'll keep the fire banked down.  I'm also going to check the contacts on the damper, I had a problem back in the spring that the damper would hum really loud, turns out the contacts were rusty from the unit sitting on the dealer's lot.  A little cleaning and it worked fine, maybe that might also be hanging the damper up.  Although it seems to shut with a loud 'clank' when the t-stat calls for it to close.

tomboysawyer

Quote from: wiam on October 15, 2006, 09:09:28 PM
Jon, it is very rare for my CB to overheat. I have the CL40.  Mine runs all summer to heat domestic and waterbeds, so not much load.  I wonder if you might have a door gasket problem. 

I got the package from CB when I got mine.  There is a flat blade shovel with wood handle.  I use this for cleaning out ashes.  (when it finishes burning off I think it will get a steel handle)  There is also what looks like a long handled hoe with a hook on the back.  That still hangs in the shed.  The other tool looks like a long handled potato hook.  These both have steel handles.  I use the latter for poking in the fire.  My favorite for poking is a piece of 1" galvanized coduit about 6' long.  My plan is to weld a small tab on the end to pull wood back to me when moving stuff in the fire. (have planned on doing this for about a year)   If you use a pipe, be aware that some coals will come out of the fire inside the pipe.

Will

Let me know if you want us to fabricate any tools for you.

Ed

Quote from: Engineer on October 16, 2006, 06:58:36 AM
There's a damper in the door which is electrically activated.  I have the thermostat set at 185 degrees, which means the damper opens at 175 degrees and shuts off once the water temp reaches 185.  I have checked the damper and it's operating fine, both in terms of when it opens and shuts, and HOW it opens and shuts.  I've also checked the door gasket and it seems to be OK as well.  The boiler is virtually new.  I had it operating in March and April for a total of about ten days, and then fired it back up three weeks ago, where it's been run intermittently.  The last three days and nights have been cold enough to fire it up pretty much continuously.

Any chance that a raging hot fire and residual heat, coupled with low heat demand, could jack that temperature up to the boiling point?

I'm not familiar with the CB furnace, but the 10 degree temp spread on the damper seems a little close.
Out Heatmor is set for 160 on to 190 off.

Ed

simonmeridew

When the damper is closed you might  test operation by quickly open the wood charging door and see if any wood is flaming (rather than just kind of smoldering away, barely glowing) If any flame is visible when the damper is closed, you have an air leak and no amount of thermostats and aquastats and other quelching/safety devices will  prevent overheating, which is what you are experiencing now. It is absolutely essential that when the damper door closes down, the fire almost go out completely within a minute or so. This must be addressed asap as overheating is not directly related to ambient temperature.
A remote possibility exists that there is a valve in the distribution system that is partially or completely closed preventing adequate circulation of the water.
Hope this helps get to the bottom of things.
simonmeridew
Kubota L4400, Farmi 351

Engineer

Might seem close, but the schematic printed right on the inside of the door says that the damper opens 10 degrees below t-stat setting.  You can set the t-stat much lower, range from 150 to 195.

Engineer

OK, I know for certain that there is no air leak.  Here's my test (aside from Simon's suggestion, which I already tried) -

Filled up the firebox last night and I made sure that the fire was blazing pretty hot, and then I shut the door and promptly went inside and turned the thermostat all the way down to 46.  There is way too much residual heat in the floor and walls (this is a timberframe home with structural panels and ICF foundation) to get the temp that low unless I left all the doors and windows open overnight.  The damper shut immediately. 

This morning I went to look at the contents of the firebox, there was just a wisp of smoke from the chimney, the entire contents of the firebox were intact but well "baked" from the residual heat in the firebox.  There were still some low coals at the bottom which ignited the fire within a couple of minutes with the door wide open.  I've experienced the "baked" effect before, where the damper stays shut on a full load of wood and the heat cooks off all the volatiles and water and you're left with some very dry, very hot and partially charred wood.

So I've effectively ruled out the air leak.  The aquastat *may* be faulty, but it was doing a good job of reading 212* when the steam was pouring out the top.  The unit did not overheat today, even though the temperature got up into the high 50's.

I'll call CB if it happens again, but I guess I'm going to leave it be for now.  These things require quite a bit of a learning curve and some experience to figure out when to stoke it and when to let it alone.

farmerdoug

Engineer,

Drop your furnace temp to the lower end when you have a low heat use cycle ie. when it is warm during the day.  I do this as the fire will over run the waster temp if set at the max.

One other question.  Is your pump circulating the hot water at all times or does the pump just turn on when the thremosat calls for heat.  If you do not circulate at all times then the fire will over run the water temp easily and your outside lines may freeze also.

Doug
Doug
Truck Farmer/Greenhouse grower
2001 LT40HDD42 Super with Command Control and AccuSet, 42 hp Kubota diesel
Fargo, MI

Robert R

I have a Hardy rather than a CB.  I have a 10-degree damper spread.  The only boil over I have had in 4 seasons was my own failure to close the bottom ash removal door so I don't know what to tell you about that but I have a great tool suggestion.  Mine came with a little square shovel (probably 5 by 5 with 3/4 inch sides) welded onto a piece of rebar.  I use it to remove ashes but when I need to poke at the logs to get them to reposition or encourage ashes to fall through the grate, the best thing I have found is a metal electric fence step in post.  You can get them for about a buck at most any farmy store or if you have access to any rebar, all one is is a piece of rebar with a small triangle on it (the triangle is my handle end in the boiler and does provide some better leverage) to prevent twisting when actually used as a fence post.  You don't need that triangle for this application so just a piece of rebar about 36 to 40 inches long for poking and allowing to stick down through the grate is the best tool I have for mine--and cheap which is right up my alley.
chaplain robert
little farm/BIG GOD

PineNut

I have a Hardy also and the only overheat was caused by a bad adjustment on the door which allowed the door to come open. This was quickly corrected. For a poker, I use a piece of one-inch rebar. Works good for me.  I run the circulation pump continuously and will be heating a green house as soon as I get it installed.

Engineer

Quote from: farmerdoug on October 16, 2006, 08:20:18 PM
One other question.  Is your pump circulating the hot water at all times or does the pump just turn on when the thremosat calls for heat.  If you do not circulate at all times then the fire will over run the water temp easily and your outside lines may freeze also.

Circulator pump runs all the time.

Thanks for the advice.  Guess I can't always just "set it and forget it".

OneWithWood

On the CL40 that we just replaced (with a CL7260) the only time we got an overheat alarm was when we burned very dry softer wood such as poplar, aspen or sassafrass with not much else in the chamber and when a wasps nest was keeping the damper from closing completey (it still clunked pretty good).  When the unit calls for heat the fast burning wood  spiked the water temp faster than the pump could circulate it.  It never boiled over. 
The air leak is still the top candidate.  An undersized pump or air in the lines could also cause the problem also.
Let us know what you find out.
One With Wood
LT40HDG25, Woodmizer DH4000 Kiln

ronwood

I have a friend that has an older CB and the damper would not close properly. Took it apart and cleaned it up and now it works fine. The only time I had a problem with my CB is I forgot to latch the door tightly and it sure did burn.

OneWithWood one thing I notice with mine is if it gets hot fire with say pine I can't open the door to the furnance when it is hot. Is this normal? I wondering if Engineer could have an issue when the furnance gets hot that a gap is created where the seal and the door comes together.

Ron
Sawing part time mostly urban logs -St. Louis/Warrenton, Mo.
LT40HG25 Woodmizer Sawmill
LX885 New Holland Skidsteer

OneWithWood

We would have problems opening the door whenever the creasote built up around the gasket.  I would imagine the pitch in pine would do the same thing.
One With Wood
LT40HDG25, Woodmizer DH4000 Kiln

Engineer

Nearly all of what I've been burning lately is pine scraps and offcuts from building.  Hmm.....   ::) smiley_idea

Another thing I've noticed is that my door drips.  Yep, that's right, it drips.  Nasty black water.  Happens when a lot of wet  or moldy wet wood is put into a hot fire.  I'll get a puddle right below the door during the burn.

Dangerous_Dan

I generally keep the windows open until the temp drops to below freezing to dump off extra heat. I have a 40 x 40 foot x 10 inch thick concrete slab with 1000 feet of PEX tubing that acts as a good thermal flywheel to suck up heat before anything boils over.
My system tries to keep the water temp constant and circulating. As the outside temp drops I adjust the aquastat to raise the temp of the water before the damper closes. On the coldest days my max water temp is 150°F coming into the building.
My damper is in the chimney above the fire and water.
The air inlet is always open otherwise I get alot of smoke.
I like fresh air and the window is my thermostat.  ;D

First you make it work, then you trick it out!

Dana

Ron, my door is difficult to open at times, I attribute this to the fire using up all the air which causes a vacuum in the chamber. With the door slightly cracked open, and a good fire going, it will pull itself closed. (If the damper is closed)
Grass-fed beef farmer, part time sawyer

Ed

Quote from: Engineer on October 17, 2006, 04:53:24 PM
Nearly all of what I've been burning lately is pine scraps and offcuts from building.  Hmm.....   ::) smiley_idea

Another thing I've noticed is that my door drips.  Yep, that's right, it drips.  Nasty black water.  Happens when a lot of wet  or moldy wet wood is put into a hot fire.  I'll get a puddle right below the door during the burn.

I think you might have found the problem. If I put in too much "scrap" wood, the fire will burn way to hot. The circ. pump can't move the water fast enough to keep it from boiling around the water jacket. I've noticed the telltale sign of this is the chimney "puffing" smoke instead of a steady column.
I also will get thr door "drippage". I think it's liquid creosote, I just scrape it up after it hardens.

Ed

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