Until last weekend I have been very happy with my stove and its performance. Never had a glitch all last season. I have always had a strong draft and kept MPD 90% closed all last year. Well last weekend I went away for 3 days so I turned dial down to #2 witch gives it a 240deg. stove temp. I wanted to see how it would last unattended for that amount of time at a low temp.
I asked my father to stop by on the 2nd day and look at it but to leave it alone if everything was OK. He stopped by and everything was OK. I came home on the 3rd day and stove is burning OK but carbon monoxide detector is going off for who knows how long!
After opening house out to ventilate and open flue I realize what I did wrong. By me turning my average temp of 450deg down to 240deg my flue cooled down and my draft decreased. I have done this for a day at low temps but never more than 24hrs. I believe if I would have opened up draft stove would have been fine.
So I finally broke down and installed a Dwyer Mark 11 yesterday! Wish I would have done it earlier, now I can moniter my draft better during varing temps. With stove running at 450deg. I have .05 draft at fully closed MPD, If i open it it goes to .10! I feel much better having it now
Interesting post- that's why Harman states not to use a MPD. Is that an airtight stove design with door gaskets ?
if it's an airtight design, without a MPD, you could have turned your stove down to 240, with the stovepipe and flue still wide open, there would be no CO fumes in the house, the remaining draft would have been strong enough to keep the fire going with no back fumes
I run my stove all year on very little air intake, without an MPD or baro, for this reason. That and it's what the manual warns and states, not to use an MPD.
the result is being able to idle the stove down to a very low heat setting, without any blowback into the room. The usual total area this stove runs at is .300 square inches of intake draft opening, i.e. 1/2 turn open on the draft knob, that is smaller than a dime opening. To illustrate just how little draft that is, here's a picture. The square marker blot is approx. .300 square inch. During the warm daytime in March or early April, I dial it down to even less than that, to 3/8 turn open, i.e. 25% less than 1/2 turn normal setting, and it will still maintain adequate draft.
this is what's possible with an airtight stove and no MPD or baro. More draft remains to control the stove with the main draft inlet on the ash door.
realize anything you put in the flow path of the stovepipe and flue pipe, will have detrimental effects to draft, and reduce it. It's basic gas flow and airflow physics. I built a lot of V8 engines and had many cylinder heads flowed on a flow bench, to see the effects of porting, and port shaping. One thing comes out loud and clear. The straighter the port, the more air it flows.
bending passages around or constricting them down, with small valves, or putting flap valves in the way, drastically cuts back the flow. A flow bench is a machine that pushes or pulls air through a cylinder head of an engine, and uses a manometer to give flow readings, in cubic feet per minute. Going from say a 2 inch intake valve, to a 2.25 inch intake valve in the heads, would yield great gains.
you could connect a flow bench to a coal stove, and get a reading, then close the MPD and that reading would go WAY DOWN due to the restriction. Basically that's what you're measuring with the manometer but you're using the chimney draft to get a reading, instead of a machine pulling the airflow through on a flow bench. Using an MPD may retain some heat but at the same time, it restricts the draft and limits how far you can close your draft before it dies, then the draft is no longer strong enough to pull the smoke out.
It would be interesting to see how far the draft falls off on a manometer, when it has to snake around all those bent passages in the a vintage baseburner. I believe this is why some of those old baseheaters won't burn wood well and smoke into the room, with those passages opened. All those bends and curves kill the draft. It creates the same low-draft effect you had with your stove, getting CO backfeed. With wood smoke it's even more sensitive, because wood smoke is heavier with lots of particulates, and needs a good draft to pull it up the chimnney.
without a damper, I can turn my stove down to the point it would simply go out, and CO would not come into the room. Keep the MPD wide open, and idle the stove down, you should be able to take it down to 240 degrees and not get CO in the house- if it's an airtight stove in good condition with good seals and pipe connections.
In over 10 years with my new stove, it never set a CO detector off once. Without an MPD, I never needed a manometer either, because the draft was always very good. The only problem I ever had with CO, was with my old stove, and old chimney, the chimney cap stanchions rotted out, and it fell down and partially blocked the outlet once.