Short chimneys are sometimes downdrafted by wind blowing against the roof. If the downdrafting problem is the result of depressurization or faulty vent design, though, extending the chimney will not help. All air moving out of a house must be replaced with air leaking into the house. Holes located high in the house, like those in the ceiling on the top floor, allow warm air to leak out. Holes low in the house, like those in the basement, allow cold air to leak in.
Tighter houses have fewer holes leaking air into the house.
With fewer holes, appliances may not have sufficient air for combustion or for venting. Venting failures, along with less fresh air, increase the risks of carbon monoxide poisoning. Improperly installed or leaky ductwork on the air return side can downdraft the chimney. In an Iowa case a family was hospitalized with carbon monoxide poisoning because they had removed the cover on the return side of the blower. Combustion air pipes to the outdoors allow additional air in most of the time, but can be overcome by wind and intermittently fail.