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Energy Saver: Furnace, Boiler & Woodstove Combustion
(continued ...)Inside your boiler or furnace panel you'll find a 'call-for-heat' signal wire from the thermostat. This is likely 24 volts AC but you can check it with a volt meter. You'll need to buy a relay with a solenoid matched to handle that voltage. The relay will be used to operate the damper actuators from a different 24 volt AC source. There is likely plenty of capacity on the incoming 120/240 volts AC circuit but there may not be enough capacity on the boiler or furnace 24 volt control circuit.
You'll need a licensed electrician to install a small 120/240 to 24 volts AC transformer with fuses on both sides of it. He can help you select the proper size for the damper actuator power. Use the 'call-for-heat' signal from the thermostat to operate the relay coil that opens the dampers. When 'call-for-heat' signal goes away, the relay contacts open and the dampers spring-return-to-close.
Now I will discuss that alternative possibility to powered dampers that I mentioned earlier. Does your burner have a provision to direct connect a duct for combustion (it must be a manufacturer's provision not something you cobble together)? If yes, that also means you have a power burner and a sealed flue without a draft-hood. Delete the second combustion air duct related to draft-hood. Make that direct connection with the one duct. If the burner connection size is smaller than what the Building Department official told you for duct size, only reduce to that size at the burner connection. If it is bigger, call the Building Department person back and have him double check his math. Now, wrap the duct with 6 inches (15 cm) of duct wrap (fiberglass with aluminum-fiber-reinforced-kraft-paper jacket) insulation rather than the 2 to 3 inches (5 to 8 cm) recommended earlier. Seal insulation ...