So from what I understand you let the charcoal burn slowly but not actually catch fire? So just like glowing red but no actual fire? Also do I leave the top on or off the grill? Will one grill be enough for a small room about the size of a normal bathroom?
Why what way are you looking to go and when ? In a car tent or bathroom ?
I'm under the impression (for example a disposable barbecue) hat you light it outside fully so all the coals flame and it smokes then when it stops smoking and the coals are ash white bring into tent it car shut the door leave it for a few minutes then enter
If using a chimney starter same method - you pour the coals into the chimney starter put paper inbetween the coals light the paper which in turn lights the coals again let it burn off until the coals are white embers then tip them into a tin bucket and place the bucket in tent or car again let the carbon monoxide build up then enter
Now it depends on how you want your death to look - do you want it to look like a suicide ? If so duct tape the gaps up so in a car the windows the air vents in a tent any dealings including the zip to the door then option leave a note
If you don't want it to look a suicide which sometimes helps family members cope with their grief - don't duct tape up don't leave a suicide note and maybe bring a pack of burgers sausages anything you can cook on a barbecue- don't cook though drop fat tings can affect the carbon monoxide output but by bringing the food it makes it look like you were preparing dinner and didn't realise the dangers of indoor barbecues and so your death will be recorded as misadventures or accidental - at least it will be in the UK courts