As has been pointed out height is not really a consideration. Here in MA they are considering bringing legislation requiring CO detectors in all residences. As usual it only took the death of a ten year old girl for anyone to think of this. [Linked Image] This death also brought about the dangers of dirct vent heating systems. In this case after a recent blizzard a direct vent was burried under the snow which of course caused CO to back up into the house.