With venting fans in two of the bathrooms replacing the heaters that were put there when the house was built, it becomes possible to turn them on to remove humidity after a shower (for example). But you have to remember to turn them off later. By getting quiet fans, it's easy to forget they are on if you are not still in the bathroom. Same with the pne remaining heater in the central bathroom.
So I went looking for a timer switch to allow the fans to be turned on, and then, some time later, turn themselves off. I have used, in the past, a mechanical timer switch and found it difficult. Mechanical timer switches use a spring to turn the knob back to zero and turn off the switch, and you have to turn it far enough for the spring to work (turn past 5 minutes), and some of the springs are strong and make it hard to turn the knob.
So I was looking for an electrical switch. But then there is the issue of how to indicate how long to wait. You could have a little keypad, or some up/down arrows to set the time, but that is a lot of overhead. I found one that simple had 4 or 5 buttons -- off, 10 minutes, 20 minutes, 30 minutes, 60 minutes. It seems that this selection would be adequate.
Unfortunately, this kind of switch becomes a large rectangle instead of just a simple small switch, so it is the "Decora" type and needs a corresponding switch plate around it. And all of our fan/heater switches are just one of two in a two-switch switch plate. So we will need to replace both switches -- for the fan/heater and for the light.
First we turn off the power at the circuit breaker box.
Then, we take off the old switch plate.
And then remove the screws holding the switches in place.
We disconnect the wires from the switches, remembering which is for the light, and which is for the heater/fan. We attach the wires to the new switches. Power comes in on one wire, to the switch and then back out on the other wire to the light or fan.
We test the switches before putting them back in the wall. (Turns out I had connected the light to the fan switch and vice-versa, so I had to swap the wires.) Once we have them correctly wired, we can put them back in the wall box.
And put the new switch plate on.
With these, it is clear which is the light and which is the fan/heater switch. Plus, I read that these larger rocker switches are better for older people than the standard toggle switch.
This process takes about an hour, even with multiple trips to and from the circuit breaker box to find the right circuit breaker for these specific lights and fans, and with the mistake of the timer switch for the light.
Update, June 2017. The timers and fans are working well in the Master Bathroom and the Back Bathroom, where we have fans that vent to the outdoors. The middle bathroom, on the other hand, still has a heater rather than a fan, and does not vent to the outdoors. It appears to me to be very difficult to run a vent to the outdoors, because of its position relative to the roof and the attic. But I put in a timer anyway. Dorothy reported the other day that it would not turn off, and it (the switch) was getting very hot. I turned it off at the circuit breaker box (circuit 14), and then replaced the timer with just an ordinary (heavy-duty) on/off switch. I suspect that the timer is mainly designed for lights, and could not handle the higher current draw of a heater. It appeared that a coil inside had badly over-heated.
The switch on the right has a little light in it (to help find it in the dark), and is the light switch; the one on the right is the fan switch.