Do Atmospheric Pressure and Air Quality Affect Burn?

 
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ytseman3
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Post by ytseman3 » Fri. Dec. 05, 2014 8:49 pm

Today the weather here is overcast, cold and rainy and my stove just doesn't want to burn quite right. I mean, the coal seems to burn slower and not as hot. It was pushing hot coals off the grate, at the same feed rate that just the day before had an inch or two of ash at full burn. Stove temp is also lower (350 deg). My draft was set at -.02 and the combustion fan plate at half open. I had the feed screw backed out 6 turns. I have tried opening up the air flap and increasing draft to -.03 and did see slight improvemant. That didn't help much so I reduced the feed more (backed out 7 turns now). This same senario happened about a week ago and just cleared up on its own then. Can the weather make the stove burn at reduced output?


 
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Lightning
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Post by Lightning » Fri. Dec. 05, 2014 10:27 pm

Temperature change can influence chimney draft which in turn can cause your appliance to behave differently. Atmospheric pressure and humidity, not so much..

 
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ytseman3
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Post by ytseman3 » Fri. Dec. 05, 2014 11:08 pm

I get these weird burn patturns where parts of the fire usually near the sides don't burn as fast, usually the glowing coals are straight a cross the grate. Here is a pic, obviously on idle now but even here you can see the uneven burn. Is this normal?

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lzaharis
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Post by lzaharis » Sat. Dec. 06, 2014 12:24 pm

The barometer rules all with the folks that have
the hand fired coal stoves and boilers as well as the stokers.

Your altitude above sea level and the coal quality have a a lot to do with it.

I live at 1,140 feet above mean sea level and some days I have
no trouble burning wood or coal but when the air flow is dead
and its warm I can forget it even with the chimney extension.

The proper term is referred to as "Pressure Gradient"

"In atmosperic sciences(meteorology, climatology and related fields)
the pressure gradient(typically of air or generally of any fluid) is physical
quantity that describes which direction and at what rate the pressure changes
most rapidly around a particular location".

"The Pressure Gradient Force is the force which results when there is
difference in pressure across a surface. In general a pressure is a force
per unit area across a surface".

The combustion blower is pushing the higher pressure air through a small surface area to
the grates and losing pressure as it passes through the grates and burning the coal.

The smaller second combustion blower on the new Keystoker boilers and furnaces
increases the amount of pressure at idle and aids in complete combustion of the coal.

Warmer air is less dense than cold air and is also harder to
move which is a huge factor in combustion as air is like water
and electricity, it is lazy and will go anywhere it can when it can.

I can have the ash pit door open and even with an empty ash pit
the burn is finicky when the weather warms.

Getting the proper combustion is like herding cats and whether
you want to micro manage it as you would need to be sure the grates
are clean, gaskets are intact, grates cemented and whether to also
manage the air shutter settings on a daily basis.

It will not hurt to stop burning for a bit and check your grates for plugged
combustion air holes from coal fines.

The biggest worry is making sure your barometric damper is
working properly for the process of combustion to work for you.

Let the fire go out and check the grates to make sure they are not plugged.

 
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Post by Pacowy » Sat. Dec. 06, 2014 1:15 pm

Overcast and cold are 2 factors that would cause the unit to run more than on sunny, warmer days. If running more winds up pushing burning coals off the end of the grate, it sounds like the fuel/air mixture may have been off to start with. The 2" of ash should be present after the unit has run continuously for a long time (30-45 minutes or more), and the weather conditions shouldn't matter much.

I wouldn't worry much about what the fire looks like at idle as long as it's staying away from the hopper. IMO combustion fans that run all of time may tell you more than you need to know about airflow patterns at the hopper end of the grate. Under load the combustion occurs primarily on the lower end of the grate. If the fire has weird patterns after running for a long time, it's probably worth checking for fines accumulation in the air chamber, and plugged air holes in the grates.

Mike

 
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Post by olpanrider » Sat. Dec. 06, 2014 1:51 pm

Your not getting enough combustion air.. clean the blower and under the grate.. try opening a door or window and see if there's a change..also check for fly ash build up in your flue..

 
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Post by ytseman3 » Sat. Dec. 06, 2014 2:30 pm

I think I'm going to take the advice about letting it go out and check the blower. I did vacuum under grates before firing up but I didn't blow out the squirrel cage for the combustion blower. Think I'll give it a good cleaning and also check the grate holes and fines while it's down. Thanks for the advice, I'll post back with results.


 
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Post by ytseman3 » Sat. Dec. 06, 2014 8:18 pm

Well, I took the combustion fan off and removed the fan from the housing that fastens to the stove. The inside of the fan blade housing was coated with dirt as was the fan blade assembly. Gave it all thorough cleaning, swept out under grates(not much dirt) and checked all the air holes in grates. There was a lot of ash and some cat hair build up on the fan, I'm fairly sure this was the problem. The stove is burning ok so far, we'll see how it goes. Thanks everyone for the help!

 
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Post by coaledsweat » Sat. Dec. 06, 2014 8:55 pm

ytseman3 wrote: There was a lot of ash and some cat hair build up on the fan,
Those squirrel cage fans can lose 80% of their efficiency when the cup gets loaded. Should be cleaned twice a year

 
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Post by lzaharis » Sat. Dec. 06, 2014 10:51 pm

ytseman3 wrote:Well, I took the combustion fan off and removed the fan from the housing that fastens to the stove. The inside of the fan blade housing was coated with dirt as was the fan blade assembly. Gave it all thorough cleaning, swept out under grates(not much dirt) and checked all the air holes in grates. There was a lot of ash and some cat hair build up on the fan, I'm fairly sure this was the problem. The stove is burning ok so far, we'll see how it goes. Thanks everyone for the help!
==================================================================================================

YAAAAYYYY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I believe one of the NEPA forum members built a furnace
filter box and fit it over the fan to keep the air clean for the combustion blower.
I do not remember who did it though :oops:

 
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ytseman3
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Post by ytseman3 » Sat. Dec. 06, 2014 11:05 pm

Yes, I have a full burn going now and it's back to normal! Nice high flames touching the top of stove and an even burn on the grates with nice bright coals.

 
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Post by Lightning » Sat. Dec. 06, 2014 11:43 pm

ytseman3 wrote:Yes, I have a full burn going now and it's back to normal! Nice high flames touching the top of stove and an even burn on the grates with nice bright coals.
Right.. Barometric pressure and humidity have minuscule bearing on stove performance.. temperature has influence on chimney drafting, warm days less draft, cold days more draft, wind also causes more draft in most cases. Usually the problem is constricted combustion air as you have discovered..

 
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Post by WNYRob » Mon. Dec. 08, 2014 8:21 am

I simply take a 4 x 12 vent filter and cut it into thirds, and just lay one over the opening of the combustion fan. Change it out every couple weeks as it gets dirty and it will keep the fan blades clean. My combustion blower is, I believe 4 yrs old, and haven't had to clean it once. And this is in the basement which is fairly dusty.
lzaharis wrote:
ytseman3 wrote:Well, I took the combustion fan off and removed the fan from the housing that fastens to the stove. The inside of the fan blade housing was coated with dirt as was the fan blade assembly. Gave it all thorough cleaning, swept out under grates(not much dirt) and checked all the air holes in grates. There was a lot of ash and some cat hair build up on the fan, I'm fairly sure this was the problem. The stove is burning ok so far, we'll see how it goes. Thanks everyone for the help!
==================================================================================================

YAAAAYYYY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I believe one of the NEPA forum members built a furnace
filter box and fit it over the fan to keep the air clean for the combustion blower.
I do not remember who did it though :oops:

 
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Post by mariohotshot » Mon. Dec. 08, 2014 10:42 am

lzaharis wrote:I believe one of the NEPA forum members built a furnace
filter box and fit it over the fan to keep the air clean for the combustion blower.
I do not remember who did it though :oops:
You can search "convection blower filter" under the venting threads. It's a filter for the convection blower, I guess it can also be modified for the combustion blower too, but what for?
Last edited by mariohotshot on Mon. Dec. 08, 2014 3:20 pm, edited 1 time in total.

 
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ytseman3
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Post by ytseman3 » Mon. Dec. 08, 2014 1:27 pm

Wouldn't the filter reduce airflow and effect burn just like if it were dirty?


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