residential furnace fan programability

Dave Faust_3

I have installed several "programable t-stats" which control when the furnace has a certain setpoint.
I'm looking to be able to have the fan run on "constant" during certain periods and "automatic" at other times.
How might I do this.
I assume there might be several methods.

Unknown

Do you have a system

with a temperature on temprature off fan control? Or do you have an Elecronic Fan Timer? Answering that will help.

Keep in mind most prorammable t'stats have an Auto setting which means the fan comes on afteer the burner fires and runs for a time. There is usually a fan on setting which means the fan runs constantly.

One of the concerns with warm air furnaces is thermal damage to the heat exchanger due to high temperatures. This is why on modern furnaces the fan comes on with a time base rather than temperature. You have to be careful so you do not damage the heat exchanger.

There are ways to control fan speed however if that is of interest to you.

carol_3

One thermostat I know of that will do pretty much what you want is the Honeywell touch screen (TH8320, for example) When you look in the instructions, you'll see that you can choose "circ" (circulate) for any of the 4 times of day (wake, leave, return, sleep). The fan can be programmed for on, auto, or circ. Circ means that the fan will run for a minimum of 10 minutes out of every hour. So if there isn't enough call for heating or cooling to get that 10 minutes, the stat will make up for it. You cannot choose when it runs.