Hotblast Year 3

Larry, how tall is your cap? Specifically, how much space between the top of your liner and the lowest point of your cap?

6"

I'm not a drinker at all L. But after this 39 pages--hell, I'll go with ya!!

Come on down.
I'm buying

Lightning wrote:Yeah, I think Paul is right. Even if the 8 inch chimney is square seems like there should be 2 inches that would be unobstructed in the 6 inch liner. But, chimney cap and gray day

I had a feeling we would find a chimney issue. Somehow those gaps where the tee meets the pipe need to be fixed. It could be robbing a huge amount of draft strength.

It's not quite 40 feet from the clean out door up to the underside of the dark gray slate cap on my chimney. The slate is bigger across and overhangs the sides of the chimney, and it's only sitting up off the chimney top the thickness of a brick at each corner.

My chimney is in the shade under the north side of a large maple tree.

When checking for squirrel nests in fall, when the leaves are still on, holding a mirror in through the cleanout door opening, I have no trouble seeing daylight on the underside of the slate on a cloudy day. If I can't see the slate cap, I know I have a leaf nest up there and have to run my chimney brush up and bust it loose.

I strongly suspect that something is not right somewhere up in Larry's chimney. I hope I'm wrong, but then we're back to what else is the cause of his problem ?

Paul

First order of business is a cleaning. It more than likely resembles his flue pipe.

The other is the 'T' going into his thimble, at the bottom of his liner, going into the thimble on the 'inside' of his chimney. Any leakage there will take draft from his furnace. Although that alone could explain the buildup we saw in the flue pipe.

Somehow those gaps where the tee meets the pipe need to be fixed. It could be robbing a huge amount of draft strength.

Although there isn't a great connection, It's pretty well sealed with the vermiculite around the gaps.
I will grab some caulk and fix it when I tear apart again this weekend.

If the draft is a problem, I'd think that only 6" gap at the top of a 6" diameter pipe loaded with fly ash/soot could reduce the gas velocity and create turbulence and maybe even backpressure?

only 6" gap at the top of a 6" diameter pipe loaded with fly ash/soot

I don't think it's loaded with fly ash and soot.
But, we will see.
It could be
When it was brand new, it wasn't loaded and I have run brushes and Never have been able to see daylight

larryfoster wrote:

only 6" gap at the top of a 6" diameter pipe loaded with fly ash/soot

I don't think it's loaded with fly ash and soot.
But, we will see.
It could be
When it was brand new, it wasn't loaded and I have run brushes and Never have been able to see daylight

If it isn't loaded with soot, then the problem is between the bottom of the liner and the back of the furnace. What was in that flue pipe indicates a low draft situation.

larryfoster wrote:

only 6" gap at the top of a 6" diameter pipe loaded with fly ash/soot

I don't think it's loaded with fly ash and soot.
But, we will see.
It could be
When it was brand new, it wasn't loaded and I have run brushes and Never have been able to see daylight

Not your fault, Larry. What you have might be fine in many situations. We're intentionally calling out things to help you get things working the way you want them

Gases cool and sometimes slow at the top. A cap does more of that.

But then again, water in the pipe is quite bad for steel and bit, and soot.

Maybe if it is part of the problem, a taller cap might help. But we'll see

Until we get up there we don't know what is there.
The cap is what came with the kit from the supplier.

We know that there's not a ton of draft and have suffered that from the beginning, I believe.
We'll figure the cause.
I hope

A cap helped me significantly. I was getting downdrafts and the cap stopped it.

larryfoster wrote:We know that there's not a ton of draft and have suffered that from the beginning, I believe.
We'll figure the cause.
I hope

SWPaDon wrote:If it isn't loaded with soot, then the problem is between the bottom of the liner and the back of the furnace. What was in that flue pipe indicates a low draft situation.

SWPaDon wrote:A cap helped me significantly. I was getting downdrafts and the cap stopped it.

The opening has to be large enough not to restrict or slow the gases.. Caps with enough can be helpful. They also make caps that work like a turbine.

Some interesting stuff out there to help in tough areas, like a city with other close buildings and such.

CoalisCoolxWarm wrote:

SWPaDon wrote:A cap helped me significantly. I was getting downdrafts and the cap stopped it.

The opening has to be large enough not to restrict or slow the gases.. Caps with enough can be helpful. They also make caps that work like a turbine.

Some interesting stuff out there to help in tough areas, like a city with other close buildings and such.

Agreed, mine is right at 6 inches.

If the cap is 6 inches above a 6 inch liner, then there is much more cross sectional area for the exhaust to exit under the cap than the pipe has to flow the exhaust.

6 in diameter x 3.1415 = circumference x 6 height of opening under the cap = 113.09 square inches, which is the total area of the opening around the liner below the cap.

The 6 inch liner has a cross section of only 28.27 square inches.

And even if the wind is blowing and closing off one side of that 6 inch high opening, half the opening still has a far greater cross section than the liner does.

If the cap is indeed 6 inches above the liner, or even just 4 inches, I don't see that the cap is causing any restriction to draft flow.

Paul