Furnance fan switch + another switch for a \\\

[pgalvin]

Greetings,

My house has forced air for the air conditioning and the heat.

One of the supplies to a 2nd floor bed room is very weak, so I am installing a fan into the associated duct. I call this the "baby fan".

I want the baby fan to turn on in 2 ways:

1. On demand when I flip a switch in the bedroom.

2. When the main house fan turns on.

As to why -- in the summer, we will probably have this fan on when the room is too warm since even if the air conditioner is not running, the air pulled thru the ducts is still cool. In the winter we only want the heat to trigger the baby fan.

How can I accomplish this? I can easily switch the baby fan on/off with an ordinary switch. I can almost as easily connect the baby fan to the main furnace fan's switch. However, I assume that if they both connected to the baby fan and the bed room switch was already on when the furnace fan turned on, this would cause a problem.

Thanks and regards.

[plugwash]

what you wan't to do is use a 3 way switch, in one position the switch connects the fan to the permanent mains supply, in the other position is connects the fan to supply for the main fan.