[genehern]

We are adding 200 sq ft to our house for a total of 1400 sq ft and are replacing the furnace. The old furnace is original and 16 years old. We recently upgraded the AC compress to a 3 ton unit.

Will we need to replace all of the ducting to accommodate the new furnace that will be a 3 ton 95% unit?

One contractor said yes one said no?

Thanks

[letmetellu]

A three ton AC is a little too much for 1400 square feet, so if you duct work is big enough for the house you have now it will probably work on the new furnace. A three ton AC should give you 1200 CFM of air from the blower. So what you need to do is measure the size of the duct just above the furnace, the measure all of the registers in every room, take this information to one of the hardware dealers (Home Depot) and have them tell you how much air the big duct will handle and then the total of all of the registers. If it is 1000 to 1100 you will be OK,