Tjernlund HS1 Gas Sidewall Power Venter Fan Side Wall Vent Systems save time and money and are excellent for electric to gas/oil, renovations, new construction or for replacing deteriorated chimneys. Side wall venting saves costly materials and labor on two, three or more story runs. Proven safety interlocks assure proper exhaust, a feature conventional chimneys do not offer in today's homes and buildings. Includes UC1 Interlock Control and PS1505 Fan Prover Switch Pair with Tjernlund VH Series Vent Hood Terminations