Physics Question

My stove is a Harman Mark I. It has narrow slots between the metal and the glass of the loading door, at top and bottom, to let in a small amount of air above the fire. This doesn't seem to provide quite enough air with a new load of coal, then provides too much for the next 10 or 12 hours after the fire has settled. (That's going with the theory that ANY air above the fire is too much.)

I am toying with the idea of getting another spinner-type air inlet and mounting it on the side of the stove, and sealing the door inlets. Then I could shut off the over-fire air. BUT -- when I close the spinner down tight against the stove side, and it heats up to 850 degrees, will it expand and lock itself so tight against the side that I won't be able to move it?

rberq wrote:My stove is a Harman Mark I. It has narrow slots between the metal and the glass of the loading door, at top and bottom, to let in a small amount of air above the fire. This doesn't seem to provide quite enough air with a new load of coal, then provides too much for the next 10 or 12 hours after the fire has settled. (That's going with the theory that ANY air above the fire is too much.)

I am toying with the idea of getting another spinner-type air inlet and mounting it on the side of the stove, and sealing the door inlets. Then I could shut off the over-fire air. BUT -- when I close the spinner down tight against the stove side, and it heats up to 850 degrees, will it expand and lock itself so tight against the side that I won't be able to move it?

Not being an engineer I wouldn't recomend changing your Harman's airflow design without writing to them (even through a dealer if need be) to get their input on your ideas. I know my TLC-2000 has small channels to let secondary air in also. (It also has slide control type vents for burning wood which I never open.)

From my post on the Short Burn Time Thread:

"The lack of gasket material in the top and bottom of the door glass allows a small amount of fresh air into the stove to "wash" the door glass. This is a very small amount of air and I really don't think it has much effect on the operation of the stove.
Proper draft regulation and decent coal make all the difference."

The stove is designed to create a swirling effect in the area over the coal to more completely burn the coal and extract more heat. Adding an over-fire air vent on the side will disrupt the flow of gases inside the stove. A question-why would you want to add secondary air to the firebox anyway? Coal needs air flow from under the coal bed.

You ask "why would you want to add secondary air to the firebox anyway?" I only want it early in the burn, when I have to open the loading door a bit to get the gasses to burn rather than build up and poof! when they finally ignite. That's more of a problem with one brand of coal than with another. More importantly I want to be able to shut OFF the secondary air for the remaining 10-12 hours of burning. Pre-baro, when I was burning with too much draft, I could hear the air whistling through the slots like a teakettle at low boil. Though I can't hear it now that the baro reduces the draft, I have to believe that there's still a significant quantity of air going in.

Others are right, however, I probably shouldn't mess with it too much. Harman paid some engineer a lot of money to refine the design, and anything I do risks unintended consequences.

Last year I packed the glass on my SF250 so no air would enter. The glass would smoke in a few hrs. I was finding myself cleaning the glass everyday in order to see the glow. Prior to this season, I repacked the gasket but left 25% of the gasket out as it was from the factory. The air wash system works again. I see no reason to pack the glass tight. It all works out in the end with your set points on the ash pan door damper.

I guess I'll leave it alone then. I don't want to be cleaning the glass all the time. Thanks for passing on the result of your experience.

My glass had been getting "black scorch marks" on it, around the perimeter. Several weeks ago, I noticed that there was no seal around the glass, so I promptly installed some fiberglass rope between the glass and door. While this seemed to eliminate the scorch marks, it seemed like I was getting more fly ash on the lower area of the door and ledge going into the firebox. So, based on what has been said here, I removed the bottom piece of fiberglass rope.

Most all of the old coal stoves had a slide damper above the fire, but it was to further fine tune the fire, acting much as a barometric damper does, but not being automatic. It would satisfy some of the chimney draft, with out the air going through the coal/fire.

rberq wrote:You ask "why would you want to add secondary air to the firebox anyway?" I only want it early in the burn, when I have to open the loading door a bit to get the gasses to burn rather than build up and poof! when they finally ignite. That's more of a problem with one brand of coal than with another. More importantly I want to be able to shut OFF the secondary air for the remaining 10-12 hours of burning. Pre-baro, when I was burning with too much draft, I could hear the air whistling through the slots like a teakettle at low boil. Though I can't hear it now that the baro reduces the draft, I have to believe that there's still a significant quantity of air going in.

Others are right, however, I probably shouldn't mess with it too much. Harman paid some engineer a lot of money to refine the design, and anything I do risks unintended consequences.

When you add coal to the stove leave a small area uncovered, where the glowing coal is still exposed. This will ignite the gases and prevent an explosion. Wait about 10 minutes and finish filling the stove.

Why secondary air?
1. You need it to burn off the methane early in the burn.
2. Later it is helpful to control the draft. If you have no secondary air the stove may function like a blast furnace and run away. Shut it and you may note a low roaring noise from the stove. When open it reduces the chance of this happening
3. Many stoves have a check damper that will admit air to the flow at the base of the stack. That is used on very cold, windy nights when the damper in the pipe is not enough to control the fire. By introducing air above the fire you reduce the air going up through the fire and cool the fire.

yes or no aside, the answer to the question is the expansion and contraction of the stove AS WELL AS the new "spinner" gizmo, will be linear so there should not be a issue of "locking-up" when hot.

Poconoeagle wrote:yes or no aside, the answer to the question is the expansion and contraction of the stove AS WELL AS the new "spinner" gizmo, will be linear so there should not be a issue of "locking-up" when hot.

Agree, everything would heat up equally.

rberq wrote:My stove is a Harman Mark I. It has narrow slots between the metal and the glass of the loading door, at top and bottom, to let in a small amount of air above the fire. This doesn't seem to provide quite enough air with a new load of coal, then provides too much for the next 10 or 12 hours after the fire has settled. (That's going with the theory that ANY air above the fire is too much.)

I am toying with the idea of getting another spinner-type air inlet and mounting it on the side of the stove, and sealing the door inlets. Then I could shut off the over-fire air. BUT -- when I close the spinner down tight against the stove side, and it heats up to 850 degrees, will it expand and lock itself so tight against the side that I won't be able to move it?

I've got a Mk I as well and I'm going to say you have another issue.

All your door gaskets good? When you shut the air intake down, it should kill the fire, not stoke it up. And no way you have enough air coming in those two little slots to feed it that much.

Do you have a baro and/or a hand damper? In my other house, I had an over abundance of draft but no room for a baro. I tried running it using just the air intake and the fire was barely controllable. Once I added the manual damper, it was manageable at least.

jpete wrote:In my other house, I had an over abundance of draft but no room for a baro. I tried running it using just the air intake and the fire was barely controllable. Once I added the manual damper, it was manageable at least.

The original post here is almost 4 years old, so my original question is moot -- I'm much smarter now, except in the political threads where I am only slightly smarter thanks to help from my conservative advisers.

But back to stoves, yes, mine was also much harder to regulate until I added a baro damper.

I never look at the original post date.

Glad to see my "diagnosis" helped even if it was 4 years late.