Replacing Trane XB80 furnace with XV95, airflow?

[steve f]

One of the estimates I've gotten recently involves a Trane XV95 replacing a Trane XB80, both 60,000 btu. As far as return ducts, and I have two 10" ducts going into the airbox. Will this be sufficient for the XV95? There will be a two ton AC unit installed along with the furnace.

[ball a/c]

The 2 10" ducts will handle 850cfm. So that's enough for 2 tons of a/c. I would be concerned about the size of the r/a grill size. The numbers are very close.

[steve f]

I've got three returns in the 1200sf space. One 10" duct goes to a single large return that's probably 30" long x 6" high (that's the grill size). The other two returns are serviced by the other 10" duct, and one of the salesmen commented that they're a standard size, I"d say the grill size is 10"x10".

I'm concerned about this because a Carrier salesman suggested installing another return, but down in the basement where the units will be located (the basement has it's own system, so didn't want to do that). I had posted on that wierd setup before, either on here or on another forum. However, I know airflow is really important, especially for the high efficiency units, and I like to get opinions that's not coming from a salesman.

[ball a/c]

One simple way to check to see if the blower needs more return is to pull off the door cover at the blower compartment. If the door has resisitence and wants to pull out of your hands and snap back on, your blower is starving for air. Another way is to have someone feel the air flow at one of the supply grills and with the fan running, pull the door off the blower compartment and see if the airflow increases. I know this sounds unprofessional, but it will give you a pretty good ideal ifyou have enough R/A.

[beenthere]

Ask the contractors that are giving estimates.
To check your static pressure.

[younghvactech]

are they hard pipe or flex steve? also check static pressure. it tells you if ducts are sized properly you can check r/a and s/a.. if you do go with xv95 you will love the variable speed motor..

[perfectheat&air]

and the quiet operation

[BaldLoonie]

But if anything is undersized, that variable speed blower will cause air noise like a plane taking off when it switches to high! 60K 90% is a lot for 1200 sq ft. The factory heat speed will try to move 1125 CFM on high heat -- through an 800 CFM return system! Can slow the blower but could get close to limit setting.

[motoguy128]

The noise from the furnace itself will be much quieter....but... VS blowers aren't magic. If the air velocity at a grill or in a duct is too high it will be noisy. And worse, the noise form the furnace may have masked noise from the air flow and at the registers. So while the system overall will be quieter, other parts of the system might seem noisier.