Secondary Air System

Great site with good info, Does anyone know how many cfm or what size blower I need for secondary air on a outdoor coal water boiler. Firebox size is 24"wide 32"deep 36"tall, coal bed is 10 to 12 "deep. How many cfm or what size blower should the combustion air be. thanks for all your input.

Hi and welcome to the forum.

I would gather to say at least 50 CFM to 100 CFM. I'd also get one with an adjustable air intake flap so you can dial it in to your needed demand or sweet spot. Grainger has a good selection.

My outdoor stove uses 150 cfm blower.I burn bit in my stove with on problemI burn about 6 tons to heat my house.The fan part number is 4C446 from graigers.
Rob

What type of boiler do you have, I just finished building one. I have a 200cfm blower.

Royall 7400 400,000 btu

Im Going to change mine around this summer.how much coal do you burn?

Pics

Nice work.Im going to add more air to my stove.I want to make my stove like a Taylor TC500 coal stove.The flue makes two passes through the stove(water jacket)
Rob

This is the inner [firebox] side of my 'Big Bertha' boiler. there is an outer layer of steel surrounding all you see here, creating a 3-4" waterjacket surrounding the entire firbox except for the loading door and ashpan area.

The fire/hot air travels under the row of square [water filled] tubes to the back of the firebox, then up and back toward the front [loading door end] of the boiler, the hot air then reverses again and travels in the pent-roof area that is still surrounded by water to the back of the boiler then out and up the chimney.. Three passes, all fully surrounded by water, all stainless steel.

Nice work Keep us updated, Lots of photos. Don't let your progress get ahead of your documentation. It happens to me all the time, people say what did it look like before? I get to ambitous, and no history. How do you figure the btu's ?

2001Sierra wrote:Nice work Keep us updated, Lots of photos. Don't let your progress get ahead of your documentation. It happens to me all the time, people say what did it look like before? I get to ambitous, and no history. How do you figure the btu's ?

first you need to know how much btu's there are in the coal your burning btu's per lb then you need to know how many lbs
are burning at one time then multiply the btu per lb to how many lbs that is burning then you need to subtract the btu's that are loss / heat loss most stoker stoves and boiler are 75% to 80% on stoves 80% to 85 % on boilers efficient so you would subtract 20 to 30 % off of the input / btu's going into the stove now you will have your output btu's coming out of
the stove hand fired will be a little less in efficiency .

So lets say the coal your burning is 13.000 btu's per lb and the stove is set to burn 4 lbs per hr that is 52.000 btu's per hr input at 100% efficiency Now subtract lets say 25% for heat loss making the stove 75% efficient heat loss is 13.000 btu's subtract that from the 52.000 the output on the stove would be 39.000 btu's per hr is what the stove is providing for
heat more btu's per lb in the coal the more lbs per hr the more heat the stove provides Plus the higher the efficiency the more btu output the stove will have