setting draft on keystoker koker

When's the best time to set the draft on a koker with direct vent? Mine was set last year by the installer then I borrowed a draft gauge from work and tightened it up a little. This year I bought a gauge and ended up setting the draft too tight, the furnace tripped off at the "safety fume switch". I opened the draft up some and have been taking readings but they seem to be all over the place (-.02 to -.06) depending on if the unit is firing or idling, outside temp. etc. For example today draft was high -.05 so I tightened up a little and it went to -.04. Next time I checked it it's -.06. I understand that it will change depending on outside temp. etc. so should I just wait until it gets colder out and adjust it then? Would it be better to adjust it when the system is calling for heat or while idling?

Claridon,
The draft setting on the direct vent is supposed to be set and locked in position. This is preset by the factory and should be checked with a manometer. The draft will vary with different conditions but should remain negative. Occasionally you will have to clean out the vent fan housing to maintain the draft but normally you shouldn't have to adjust the vent opening.
I put a rehostat on my vent motor which does allow me to dial my draft to where I want it. My vent is locked in the fully open position. If you want to take a look at my setup, send me a PM.
-Len

I understand the vent should be a "set it and forget it" deal on these furnaces. I was making adjustments to try and make mine as efficient as possible. When I set it it was fine but at some point it changed which caused the furnace to trip off. I opened it back up but am trying to figure out when the best time to set it would be. When it's firing hard? My installer set it when he installed the unit but I borrowed a draft gauge from work and reset it last year. I didn't have any issues last heating season and I cleaned the unit this past spring so I'm sure it's clean. I've heard of others putting a rheostat on the exhaust blower but doesn't that do the same thing as adjusting the vent?

Claridon,
I don't know when the best time is to set your vent baffle. I've been running mine fully open and simply varying the motor speed to give me the optimum draft. So I can't answer that one.
As far as running a rheostat vs. using the baffle for draft control, I think the rheostat is better. Running the motor at full speed and then restricting the air flow with the baffle creates unnecessary turbulence in the vent system. Not a good idea with flyash in the vent. Using the rheostat allows me to slow the motor down, smoothing out the air flow, reduces the amount of flyash picked up, reduces the sound level of the direct vent system and allows me to easily adjust the draft as needed.
It's interesting that on page 2, item 16 of the old Keystoker Koker direct vent operating instructions it states "On all top vent direct vent models, the exhaust motor is equipped with a rheostat." So apparently this used to be a standard feature.
I hope one of the other guys can help you with your question about when to adjust your vent baffle.
Also, I wouldn't hesitate to call Keystoker. They've always been very helpful when I've talked to them.
Good luck,
-Len

I don't see where there would be much (if any) difference between varying motor speed and varying the damper. Either way you're varying the amount of airflow, whether you change the speed on the motor or change the setting on the damper, net result is air flow changes and under certain conditions draft changes. For a given damper opening/motor speed air velocity stays the same. Now... if only there was a simple, cheap way to put a control scheme in place where you could maintain a constant draft reading either by varying motor speed or damper setting... that would be the hot setup.

Charlie