How many CFM is your stoker fan motor?

Mr.Ark · Post by **Mr.Ark** » Sun. Mar. 17, 2019 8:23 pm

Hello,
I have a hand fired coal/wood boiler and I’m trying to match the air draft fan to some sort of BTU out put. It currently has a 75 cfm blower that works for wood and coal.
I think it is burning the coal too fast and too hot. My unit has a very big firebox that can hold around 150-200 lbs of coal. When it’s burning really good it runs the stack temps up to 400-500 degrees from the stick on thermometer. It is putting out plenty of heat but wasting a lot too.
I only need about 150k btu max and am thinking that a smaller draft motor would be better.
Does anybody know what a stoker uses (air cfm) when the output is around 150k per hour
Thanks in advance
Drew

McGiever · Post by **McGiever** » Sun. Mar. 17, 2019 10:24 pm

You're trying to compare apples to oranges...

Forget the fan for hand fed coal...blank off it's hole completely if wood is out of the picture for good...natural draft is all you'll ever need for hand fed coal.

Mr.Ark · Post by **Mr.Ark** » Sun. Mar. 17, 2019 11:25 pm

McGiever wrote: ↑
Sun. Mar. 17, 2019 10:24 pm
You're trying to compare apples to oranges...

Forget the fan for hand fed coal...blank off it's hole completely if wood is out of the picture for good...natural draft is all you'll ever need for hand fed coal.

This is a sealed firebox. There is no other way to let air in without some fabrication of the boiler.
What I’m trying to figure out is how much of a volume of air is needed for the given btu output.
More air or less air will control the burn rate.
Right now I’m experimenting with closing off some of the air because I think the fan is running the coal too hot.

McGiever · Post by **McGiever** » Sun. Mar. 17, 2019 11:43 pm

Mr.Ark wrote: ↑
Sun. Mar. 17, 2019 11:25 pm
This is a sealed firebox. There is no other way to let air in without some fabrication of the boiler.
What I’m trying to figure out is how much of a volume of air is needed for the given btu output.
More air or less air will control the burn rate.
Right now I’m experimenting with closing off some of the air because I think the fan is running the coal too hot.

I see, I'm sensing the fabrication aspect is not a choice at this point either.

Hope you find your answer.

Mr.Ark · Post by **Mr.Ark** » Sun. Mar. 17, 2019 11:47 pm

McGiever wrote: ↑
Sun. Mar. 17, 2019 11:43 pm
I see, I'm sensing the fabrication aspect is not a choice at this point either.

Hope you find your answer.

The first thing I might try is to run it with a chocked off air hole to slow the burn down.
After that I could fab a chain style draft stopper like the old units had. I can’t remeber what there called right now. I think the new DS units have something like that currently.

McGiever · Post by **McGiever** » Sun. Mar. 17, 2019 11:55 pm

Mr.Ark wrote: ↑
Sun. Mar. 17, 2019 8:23 pm
I have a hand fired coal/wood boiler. My unit has a very big firebox that can hold around 150-200 lbs of coal.

That is a really bad idea to force feed air into 150-200 lbs. of burning anthracite. You really want to "feather" the air control, not "force feed"

Mr.Ark wrote: ↑
Sun. Mar. 17, 2019 11:47 pm
The first thing I might try is to run it with a chocked off air hole to slow the burn down.
After that I could fab a chain style draft stopper like the old units had. I can’t remeber what there called right now. I think the new DS units have something like that currently.

ETA:
You cannot add a bimetallic chain damper on a wet boiler wall and have it work correct.

You need to have threaded pipe collar for wet immersion on top horizontal surface of boiler with a long chain down to operate the below fire damper by the top mounted Samson Valve. https://www.samson.de/document/e05300en.pdf

swyman · Post by **swyman** » Mon. Mar. 18, 2019 9:16 am

Edited.....

McGiever · Post by **McGiever** » Mon. Mar. 18, 2019 1:17 pm

See my ETA (edit to add) above...

McGiever · Post by **McGiever** » Mon. Mar. 18, 2019 1:26 pm

swyman wrote: ↑
Mon. Mar. 18, 2019 9:16 am
I have 2 stokers and they each have a 65cfm fan but like others have said it is throttled down with a cover plate. Usually the gate is covering around half the intake.

This does answer the question, but is not good info for the problem.
Huge differences exist here...flat grate stoker bed with 2 lbs. coal on grate does not equal a hand fed with a 150-200 lb. coal charge in it...

Just like you can power-vent a stoker...but never a hand-fed...amount of glowing coals has different air rules.

Take whatever you want from this and leave the rest.

Mr.Ark · Post by **Mr.Ark** » Tue. Mar. 19, 2019 12:32 am

McGiever wrote: ↑
Mon. Mar. 18, 2019 1:26 pm
This does answer the question, but is not good info for the problem.
Huge differences exist here...flat grate stoker bed with 2 lbs. coal on grate does not equal a hand fed with a 150-200 lb. coal charge in it...

Just like you can power-vent a stoker...but never a hand-fed...amount of glowing coals has different air rules.

Take whatever you want from this and leave the rest.

I am going to play with the air volume some.
I just covered half the fan intake to reduce the air flow and I’m going to see how that burns.
I’ll report back after a few days.

Part of the problem that I had before was with clinkers forming and filling up on the bottom of the fuel bed. I think that was because it burned so hard and hot with too much air.
Thanks again!