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. Fan-powered combustion air kits which operate whenever the appliance burner is on force air into the furnace room for combustion and for venting and are more reliable than combustion air pipes. Fan-powered combustion kits can be professionally installed on water heaters and furnaces. Be cautious though, adding a fan to only one appliance, can increase the risks of spillage from other heating appliance vents.
Heat exchangers are balanced systems, and exhaust the same amount of air as they bring in.
They furnish fresh air for you to breath, but they do not keep the house from being depressurized. Call a qualified heating contractor to check the house and the heating systems. These strips have no audible alarm and should be used along with a carbon monoxide detector. For more information request other notes in the Carbon Monoxide series.