I have a two level townhouse with heat/ac. The thermostat is downstair. My question:
Can I install another thermostat upstairs to constrol the heat/ac and turn the switch of
The downstair thermostat to off.

Yes but you better be ready for a huge bill from the local HVAC control expert.

Usually they will have to install a special control panel that will accept dual thermostat imputs and a remote selector located at both thermostat stations.

So the answer is yes it can be done. But I would not want to pay for it.

Now a possible solution is to use a Honeywell thermostat with a remote but you will have to research that yourself.

Catalog (http://customer.honeywell.com/honeywell/UI/Pages/Catalog/ApplicationCategory.aspx?Catalog=Homes&Category=HVAC+Zoning_130&ChannelID=%7b2EB2F178-20ED-44E0-97FB-CCFB4218DD64%7d)