Ok.... baaaad placement co will pool in lowest places in home when the air is still hence no higher then three to four feet from floor and no closer then six feet from any carbon base fueled appliance yes this includes fireplaces and wood stoves...natural gas detector highest point possible its lighter then air and seeks highest point possible and I shoulda phrased it differently.. don't get a co detector combo at all see previous statement... trust me I deal with these daily