Manometer shows half draft with load door open

I received the manometer via the loan program last night. Hooked it up after the nightly coal loading. I have a hole in the smoke pipe about 15" above the stove I placed the low side of the manometer on.

Here are my results (burning Bituminous coal in hand-fed stove in basement, 16' tall SS chimney (6" dia.) on exterior wall, no dampers):

Draft after loading with major yellow flames and 600* stove = 0.09"
Draft 3 hours after load when volatile flames are mostly gone, just blue flames, 500* stove = 0.06"
Draft 12 hours after load, before fresh load, 200* stove = 0.03"

This cycle seemed to repeat itself this morning as well. As far as I can tell, I have plenty of draft. Certainly not marginal like I was thinking. I've seen some posts that say hand-feds draw up to 1" of wc, but I think they meant 0.1". Seems like I'm right in that range.

Here's my question - Whenever I open the load door, my draft drops by exactly half of what it was with the load door shut. This happens at high fire and low fire both. I would expect that it would eventually drop with the load door open due to colder air input affecting the chimney draft and less air being pulled thru the coals. But the draft drops immediately. And as soon as I shut the door, the draft instantly climbs back where it was.

Can someone shed some light on why this is happening? Is the tube in the smoke pipe able to "see" the room pressure with the load door open? Or is my chimney cooling instantly on opening the door to reduce the draft?

Is it normal? Does it explain my problem with smoke rollout? Thanks.

Steinke

Hi Steinke, I'd check your heat exchanger for soot build up. If you open your loading door which has to be what// ? 12" square at least, then you should see zero draft, Unless your house is really tight, so first open a window then do the open door check again.

But I'd bet that you have a restriction between the door /firebox and the flue where the manometer is reading.. Just for grins pull the manometer and make sure it zero's itself.

Let us know what you find.

Greg L

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Your stove is under a vaccum and the manometer is reading the vaccum in the pipe with a certain amount of vaccum in the stove when it's all closed up.

Once you open a door or draft hole, the pressure will decrease by a certain amount and could drop to next to nothing.
The pressure in the pipe is almost the same as the pressure outside the pipe since now you have a large opening in the bottom of the stove.

Due to heat rising, there will still be some draft being drawn thru the stove and up the pipe.

Mine does the same thing when changing the ash pans, it drops way down to almost 0-.02.

Nothing to worry about, that is just the way pressure/vaccum works. As long you don't get a downdraft when the door is open...

I tried opening a nearby window, but it did not change the manometer reading at all. My house is not very tight.

I checked to make sure the manometer was zeroed - it was a little off, but pretty close. I zeroed it again and I'm still getting about the same readings.

So I pulled the smoke pipe off, but absolutely no blockage of this pipe or the stove collar. Heat exchange tubes are very clean. Smoke pipe is spotless. This bit coal actually burns quite clean (haven't cleaned inside smokepipe for 2 months).

So I wonder if my baffle plate is causing the problem. I slid the baffle plate to the front of the stove, and here are the results:

Draft with load door shut and baffle in place - 1.5+mm
Draft with load door open and baffle in place - 1.0mm
Draft with load door open and baffle slid forward - 0.6mm

As the back half of my stove collar sticks down into the stove about 1-1/2", and my baffle plate is very high in the stove (only about 2" between the baffle and the collar), maybe I have too small of space for exhaust to easily flow, and it's too restrictive, even when slid forward. The baffle is big enough that some of the flue pipe is still "covered" even when I slide it forward. Maybe that's causing my smoke rollout.

Going to try to take the baffle out completely, but stove's too hot right now.

Steinke

I wouldn't mess with it. You will have a certain amount of draft just because the hot air is rising up the chimney. it is expanding and will have a lower pressure compared to the room.. I think the baffle proves that the stove is clean. I didn't remember about your built in baffle.

Greg.

Based on the conversion factor you are seeing ~ -.02" WC with the door open and the baffle slid forward... that seems about right to me.

Also since it does change the right direction when you slide the baffle, I would suspect things are as they should be. It seems the smoke roll out issue may be helped by removing material from the baffle to open up flue.... but I wonder if that is going to mess up the operation of the stove. It seems based on the cleanliness of the baffle and pipe that something is working right.

I guess you can tell more by removing the baffle and operating for a bit to see how it behaves, I would suspect there is going to be a trade off.

Have fun with the science project.