We are installing a woodburning fireplace with two heat ducts to other rooms. There is a fan on each dust. We want to wire a coolstat in so that when the temperature reaches a point it will turn the fans on to circulate the heat.

Honeywell Farm-O-Stat AirSwitch Controller T631A 1022 - eBay (item 250317915403 end time Nov-07-08 12:52:35 PST) (http://cgi.ebay.com/Honeywell-Farm-O-Stat-AirSwitch-Controller-T631A-1022_W0QQitemZ250317915403QQihZ015QQcategoryZ53296 QQssPageNameZWDVWQQrdZ1QQcmdZViewItem)

This item will turn on the fans when the temp gets from 70 to 140 degrees.

This means that the fans will not turn on until the temp goes to at least 70 minimum or 140 maximum. It is adjustable in that range.

That means that if you set it at 70 the temp will have to be at least 70 around the wood fireplace to kick the fans on.

There will be directions on the paperwork that comes in the box.

This one is more expensive but offers a bigger range of adjustment.

HONEYWELL T631G 1059 FARM-O-STAT RANGE 35 TO 100F - eBay (item 350075568954 end time Nov-28-08 13:47:00 PST) (http://cgi.ebay.com/HONEYWELL-T631G-1059-FARM-O-STAT-RANGE-35-TO-100F_W0QQitemZ350075568954QQihZ022QQcategoryZ42911 QQssPageNameZWD1VQQrdZ1QQcmdZViewItemQQ_trksidZp16 38Q2em118Q2el1247)

Here is the Honeywell doc showing the different units available.

http://customer.honeywell.com/techlit/pdf/63-0000s/63-1089.pdf

More info and a wiring diagram.

http://customer.honeywell.com/techlit/pdf/60-0000s/60-2214.pdf