Check those furnaces and install a carbon monoxide detector
Older furnaces and even some newer models must be checked annually for proper combustion air and operation. If oxygen supply to the furnace is blocked or restricted, “incomplete combustion” of the fuel occurs causing malfunction and emittence of high levels of deadly carbon monoxide. Inform your family, coworkers, neighbors, friends, and employees and possibly save a life. Carbon monoxide is a bi-product of the combustion process when you burn natural gas or propane to heat your home or office. Cracks in the heater and improper venting can be dangerous and even deadly. Carbon monoxide can kill you in your sleep without you knowing. Having a carbon monoxide detector in your home and office and having your furnace or heating system inspected often is recommended.