Replies

1. 
   BillHartmann | May 03, 2009 11:28pm | #1

   While I call it a humidistat. What you need to do is to check that it has contacts that close on Rise. So have single pole double throw contacts and can be used for either purpose.

   But there are catalogs that call humidistat that close on Rise "de-humidistat's". But to me, from an engineering background, that is a terrible corruption of terms.

   You don't use a "de-thermostat" to run of the AC or to operate a cooling fan.

   And if I did not stop myself I would go to much longer lengths about how that terms is bad.

   So back to your question.

   The "simplest" way is to just replace the vent fan with one that has that feature built in.

   Barring that the contacts on the Close on Rise HUMIDISTAT are just wired in parallel with the wall switch. And in that case I would replace the switch with a timer. That way either the switch will turn it on or humidity. Thus you can run the switch on a time for oder removal and it will automatically vent when the mositure level gets high enough.

   .
   William the Geezer, the sequel to Billy the Kid - Shoe
1. 
   fingersandtoes | May 04, 2009 12:17am | #2

   I should have titled this "Dumb Electrical Question" as I still am not clear.

   There is nothing wrong with the fan or its controls, I'm just curious. It came up when I decided to replace the switch with a timer, as you suggest, and thought I would look into the box to see if there was anything special about how the existing switch was wired - which there wasn't.

   So bear with me: If the timer (or wall switch) is on and the humidistat is on don't I have two hot feeds to the fan at once?

1. 
   BillHartmann | May 04, 2009 01:13am | #3

   So you already have the humidistat. I thought that you where wanting to add one.And your humidistat is a separate unit and built into the fan.In that case there are several options of how it is wired. In all case the timer and humidistat are electrically in parallel. That is either can turn them on, and both have to be off for the fan to be off.Off hand I can think of several ways that it can be wired. Power comes into the switch box. From their you have 3 wire cable to the humidistat. Hot, switched, hot and neutral to the humidistat there it connects between the hot and siwtched hot. And from their 2 wire switched hot and neutral to the fan.Or with power going to the humidistat with a 3 wire to the switch and 2 wire from the switch to the fan.Or power coming into the fan, with a 2 wire connection switch leg to both the switch and the humidistat. But typically a fan wiring box would not have enough space for that.Or power to the humidistat to and a 2 wire switch leg to the switch and 2 wire switch power to the fan.And several other combinations. Might even do all of the wiring in a ceiling light box..
   William the Geezer, the sequel to Billy the Kid - Shoe

1. 
   fingersandtoes | May 04, 2009 02:30am | #4

   Thanks. I should be able to figure out which now. No better way to spend a rainy Sunday than poking around in a live outlet with a metal handled screwdriver!