Rewire attic fan from switched to always-on

Question

I have an attic fan wired to a thermostat that I'd like to come on whenever it's hot enough. The problem is, the fan is wired to a circuit that's operated by the light switch for the stairs into the attic, which also controls the light at the top of the stairs, as well as a pull-chain light in the attic. I don't want to have to leave the light at the top of the stairs on to get the fan to run! I also don't want to convert that light to a pull-chain light, since it's the only light in the stairs, and at the top. There's another switch installed just before the fan, apparently for code purposes, but it doesn't make much sense to me to only have the fan live when the wall switch in the stairs (and cosequently the light) is on.

Is there an easy way to convert the switched-hot attic fan to always-hot, while keeping the two light fixtures between the fan and the switch as switched-hot? I say always-hot, but I would leave the final switch operating the attic fan only in case of emergency.

Answer 1

Supply that fan switch you say is fitted for code purposes from the supply to the light switch, it will then be on all the time depending on its thermostat setting.

Leave the other light switches as is.

Answer 2

There are ways to wire up what you want but the scheme will depend entirely on how the live power feed comes to the existing circuit. To a secondary extent there is a dependency upon how the fan is wired into the existing lighting circuit. I will give a general overview of a couple of scenarios but you will have to provide decent photos of the following things before specific help can be provided.

1. Photo of the existing switch wiring, both the switch itself and a picture looking into the back of the electrical box.
2. Photo of the existing light wiring, both the light connections and a picture looking into the light junction box.
3. Photo of the electrical box there the fan wiring intersects with the lighting circuit if it is not included in the photos from the above two items.

Case of live power feed into the switch location electrical box:

In this case it will be necessary for you to run an additional electrical cable (14/2 wGND or a 12/2 wGND to match existing wiring size from the switch box to the switch box by the fan.

Case of live power feed into the light electrical box:

In this case it will be necessary for you to run a new electrical cable from the light box to the switch box by the fan, unless the fan wiring already directly enters the box at the light.

Answer 3

Put in the lowest power bulb you are allowed to in the stairs light and leave the switch on. This would be some Edison base LED.

From the existing light box run a short cable to another box for a higher power light which would effectively illuminate the attic. The second fixture would be a ceramic base with pull chain. A base with an integral socket wouldn't hurt, in case you ever need to use corded tools in the attic.

Answer 4

Problems like this used to be unsolvable, but are now the realm of smart switches.

You'll need a suitably matched set of smart switch, and either smart fixture, module or bulbs which can communicate with the smart switch. This communication needs to be either wireless or via powerline signaling, since you have no wires to spare.

Then, you rewire it at the switch so all blacks (including the switch's) go together as always-hot and all whites (including the switch's) go together as neutral.

At this point, any dumb lamps will be on continuously. You then replace them with smart lamps which answer to the switch.

Simpler is to wire it this way, but omit the switch altogether. This means the bulb will be on 24x7, which is both a significant cost and a fire hazard if it's last century's incandescent bulb. Using the rule of thumb of $1 per watt per year for always-hot loads, I say just slap a 4W LED light up there and call it good.