When I first started in this hobby, I lived in a very drafty house. Curiosity got the better of me one day and I fired up a .15 size motor. It ran for less than 10 seconds at perhaps a high idle. The exhaust smoke traveled the length of the house, down the staircase and then back the full length of the house. It set off all 6 smoke and 3 carbon monoxide detectors along the way. Even short engine runs in the house can cause CO levels to become dangerous.