Secondary Air Distribution System

Re: Secondary Air Distribution System

PostBy: hotblast1357 On: Mon Aug 04, 2014 7:38 pm

wsherrick wrote:You're welcome. I'm fairly sure that the pipe is plenty hot enough to heat the incoming air as soon as it gets in there. The prevailing idea is that the air needs to be hot so it will not rob heat from the fire before it is able to get hot enough to burn the gas effectively and the draft takes it and the unburned gasses up the chimney. Hence the importance of having the air as near the top of the fire bed as possible.
Germer Stove Company had another concept of introducing the hot secondary air right into the fire bed instead of over it. Their fire pot had vertical slits from bottom to top cut into the sides of the fire pot. The air was introduced that way. I don't know which system worked better.

Here is a rusty example of the Germer Hotblast design for secondary air.



Couldn't you somehow leave cracks inbetween the fire bricks of our new stoves to do what that does
hotblast1357
 
Hand Fed Coal Furnace: hot blast 1357M
Coal Size/Type: anthracite nut/pea
Other Heating: oil furnace

Re: Secondary Air Distribution System

PostBy: Lightning On: Mon Aug 04, 2014 8:11 pm

hotblast1357 wrote:Couldn't you somehow leave cracks inbetween the fire bricks of our new stoves to do what that does


The small gaps between the bricks get filled in by ash material in a matter of a couple days because of the attitude of the sloped fire bricks AND the ledge that the grate frame sits on... Its interesting you bring this up. With a brand new fire after a total clean out, It takes a couple days for my furnace to achieve its best efficiency. I see this with the variance of temperature between the flue pipe and the over the load door temperature. During the first day of a brand new fire after clean out, the difference between the pipe and over the door temp is only 50 or 60 degrees. For example, I'll have 160 degrees on the pipe with 210 degrees over the load door.. As the days progress, this temperature gap will widen. After a week, I'll see a 90 - 100 degree spread. With 160 on the pipe I'll see 250 - 260 over the load door. I've seen as much as a 150 degree spread while pushing it hotter after a full week of use. Like 200 on the pipe and 350 over the load door.

I've come to the following conclusion about this..

During the first day, some combustion air misses the coal bed by taking paths thru gaps in between the bricks and also gaps around the grate frame, causing a loss of usable combustion air.. This unused combustion air is also carrying heat up and out the chimney making for a loss of overall heat output to the living space.

After a week, ash has settled into everywhere causing incoming combustion air to take a path up thru the grates and into the center of the coal bed exclusively. In this situation as much of the available oxygen is used for combustion as possible, making it more efficient.

I see this temperature gap widen inside the first week with every new fire after a total clean out..
That's my observation on that whole thing.. :)
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

Re: Secondary Air Distribution System

PostBy: hotblast1357 On: Mon Aug 04, 2014 8:32 pm

Is there any way to get the air from under the grate, say I push my firebricks to the back all the way, this will leave a gap in the front between the stove wall and firebrick, can I run some small pipe up this channel, then 90 it back and run pipe like u have with the holes along the tops of the fire brick? Or does the secondary air have to come from outside stove? I would think with getting the air from below it would be pre heated rather well, I'm just so nervous about drilling holes in my stove, and I burn wood in the shoulder months, I am installing the glass over my door holes so I won't be able to use these for over fire air anymore
hotblast1357
 
Hand Fed Coal Furnace: hot blast 1357M
Coal Size/Type: anthracite nut/pea
Other Heating: oil furnace

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Re: Secondary Air Distribution System

PostBy: Lightning On: Mon Aug 04, 2014 8:50 pm

A fair amount of secondary air is needed for wood.. Its hard to say how well the arrangement you describe will work since there wouldn't be any way to regulate the ratio of primary and secondary air.

I know its scary to start making holes and I wouldn't advise you do it unless you are confident about it. I was sacred too. With my water coils in the way I only had a 1/4 inch in three directions for error. I measured 4 times, looked at it from every angle I could think of and made the cut. Luckily it worked out. :)
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

Re: Secondary Air Distribution System

PostBy: hotblast1357 On: Mon Aug 04, 2014 8:59 pm

From what I've been reading it seems like yours runs best at 15-20% open? Or does it very? Mostly all stoves from the factory don't have adjustments for tube air controls, I guess its just finding the right ratio
hotblast1357
 
Hand Fed Coal Furnace: hot blast 1357M
Coal Size/Type: anthracite nut/pea
Other Heating: oil furnace

Re: Secondary Air Distribution System

PostBy: Lightning On: Tue Aug 05, 2014 7:22 am

You probably noticed the caps I use to regulate the amount of secondary air I use. During cold weather burns, I have the holes open for the first hour after a shake and load to burn off volatile gases that are being baked out.. after that I put the "salt and pepper" caps on to allow a small amount of oxygen to help turn CO into CO2.. During warm weather burns I leave the holes completely open. The extra heated air mass that isn't contributing to combustion maintains draft in the chimney for me. This way I can idle it down to hardly any heat output during the day and then rev it back up overnight.
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

Re: Secondary Air Distribution System

PostBy: steamshovel On: Tue Aug 05, 2014 7:25 am

with wood you'd want to adjust the primary/secondary drafts to get minimum smoke from the chimney, to not plug up the flue with creosote quickly. those magnetic thermometers come in handy, they are marked for the optimum burn range to reduce creosote deposits.
steamshovel
 

Re: Secondary Air Distribution System

PostBy: hotblast1357 On: Tue Aug 05, 2014 9:20 am

Maybe I'll just bite the bullet and drill the holes lol
hotblast1357
 
Hand Fed Coal Furnace: hot blast 1357M
Coal Size/Type: anthracite nut/pea
Other Heating: oil furnace

Re: Secondary Air Distribution System

PostBy: Lightning On: Tue Aug 05, 2014 9:40 am

I used a hole saw for metal.. it attached to my drill. Take a pipe that you plan to use and line it up with the hole saw bit and get it as close to the same size as possible.

For the secondary pipes I used metal electrical conduit. Worked great! I also used compression fittings to attach it to the stove body. I think all that information is in this thread somewhere.
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

Re: Secondary Air Distribution System

PostBy: hotblast1357 On: Tue Aug 12, 2014 9:44 am

Lee, what kind of equation did you use to figure out the 25 1/4 in holes are equal to a 1/1/4 pipe, I'm using a 3/4 in pipe and want 1/8 in hole, 18 inch long pipe
hotblast1357
 
Hand Fed Coal Furnace: hot blast 1357M
Coal Size/Type: anthracite nut/pea
Other Heating: oil furnace

Re: Secondary Air Distribution System

PostBy: Lightning On: Tue Aug 12, 2014 10:01 am

Cookin french toast for the kiddos... lol I'll hook ya up with that shortly :)
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Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

Re: Secondary Air Distribution System

PostBy: hotblast1357 On: Tue Aug 12, 2014 10:04 am

Send some over this way!
hotblast1357
 
Hand Fed Coal Furnace: hot blast 1357M
Coal Size/Type: anthracite nut/pea
Other Heating: oil furnace

Re: Secondary Air Distribution System

PostBy: Lightning On: Tue Aug 12, 2014 10:55 am

hotblast1357 wrote:Lee, what kind of equation did you use to figure out the 25 1/4 in holes are equal to a 1/1/4 pipe, I'm using a 3/4 in pipe and want 1/8 in hole, 18 inch long pipe



Area = Pie (3.14) times (radius squared)

So for the 3/4 inch pipe Area = .44 sq in
1/8 inch holes are .012 sq in
1/4 inch holes are .049 sq in

So according to this, it would take roughly 36 holes at 1/8th inch to equal the area of the 3/4 inch pipe (inlet).. You would need to space them 1/2 inch apart for the 18 inch length of pipe. This doesn't allow for turbulence around the small holes slowing air flow. I'm not sure if it would be enough. But its worth a try..

I would use bigger holes. 1/8th inch holes are pretty small.
It would take 10 holes at 1/4 inch per hole to roughly equal the area of the 3/4 inch pipe. You can add a couple more since turbulence around the holes will slow down air flow a little. You could use 12 holes (1/4 inch) spaced 1.5 inches apart for the length of the pipe..

Be keeping the collective small hole area in check with the size of the pipe, it will help with getting an even distribution down the length of the pipe..
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

Re: Secondary Air Distribution System

PostBy: hotblast1357 On: Tue Aug 12, 2014 11:18 am

Thanks man, I'll prob go with the 1/4" holes
hotblast1357
 
Hand Fed Coal Furnace: hot blast 1357M
Coal Size/Type: anthracite nut/pea
Other Heating: oil furnace

Re: Secondary Air Distribution System

PostBy: Lightning On: Tue Aug 12, 2014 11:32 am

hotblast1357 wrote:Thanks man, I'll prob go with the 1/4" holes


Yer welcome partner.. so you decided to take the leap and make holes? Don't forget you'll need a way to regulate the new secondary inlets.. :)
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut/Stove Size Mix

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