I think you mentioned it in a different thread - but I'm lazy. Which cannister stove do you have that you are able to simmer? My PocketRocket is a little better than my Gigapower, but neither or them simmer even remotely as well as the DragonFly. I've used the DragonFly to heat up my tent, but there's that carbon monoxide thing.....
I have the Primus Mini Duo, a stove/lantern combination. I've had others use the Pocket Rocket and I see they don't simmer quite as well as mine.
I think the Dragon Fly makes noise and it's a coleman fuel type stove right?
The CO thing is understanding why and when the stove produces CO.
The most output of CO comes from when you prime the stove, that fuel burns very unefficiently and can drive the CO in a snow shelter right up to 135 ppm by the time the stove gets going. The next biggest producer of CO is running the stove hot enough that the flame touches the pot. This causes incomplete combustion also and can easily double or more the amount of CO produced from the same stove on simmer.
From the testing I've done, my canister stove was below 5 ppm on simmer and was 15 ppm on a reasonable high setting (not where the flames come up the side of the pot).
I've tested it with other peoples canister stoves as well and found the same results. I don't know what models those were though.
I also tested with my buddies Whisperlite and we had around 15 ppm on simmer and 28 ppm on a reasonable high setting.
This is all with proper venting and that isn't as much as you would think. We had a 1" diameter hole at the top of the snow shelter and the door had a small gap at the bottom. The top of the door was below the floor so the amount of venting was determined by the size of the ceiling vent.
We found the air going through the vent to be traveling at 5 mph.