We live in an old 2 storey house.Thermostat is in the hall on the second floor. We have just installed a new gas furnace and now the temparature on the second floor is about 5-10 degrees warmer than the first floor. Should we move the thermostat to the first floor?

Hmmm...

If I follow you here, you are asking if you should move the thermostat to the colder area (1st floor) because the 2nd floor is 5-10 degrees warmer, right? By my thinking that would just end up resulting in an even warmer 2nd floor, right? Here, by comparison to the 2nd floor, the colder 1st floor would only serve to have the furnace stay on longer to satisfy the thermostat...just make the 2nd floor even hotter as the 1st floor got comfortable!

I'm thinking that you may want to check the air vents/registers in each room and see if they are adjustable. If the registers are adjustable I would start by opening the ones on the 1st floor wider and closing the ones on the 2nd floor a little bit....see if that makes a difference. Using this approach and purchasing a cheap battery powered room thermometer you should be able to figure a decent balance between floors. If you don't have adjustable registers then you may want to look into purchasing some (available in multiple sizes). There are other answers, too, but this is the easiest place to start.

In some cases, you might need to install dampers (flow control) in main trunk lines. In rare cases, we'll even install fans to "boost" air flow to certain rooms or floors.

Anyway, let me know what you think, OK?

Mark