5 Ton Rudd/Lennox/Heil AC how much RA is needed?

[sidneyb]

I have 4 contractors bidding the replacement of my 2 AC systems.

Downstrairs is 17 year old 5 ton Goodman
Upstrairs is 17 year old 3.5 ton Goodman
4400 Sqft 5 BR in Houston Texas

The existing systems both have 1 Return Air 25" x 25" grill connected to 18" flexible hose to AC system in the attic.

Only rooms upstairs are 4 bedrooms. Much of upstairs is open to the downstairs.(great room in the middle of the house)

The Rudd provider is telling me I need to add RA for the downstairs. The way the house is built it is impractical to add another RA downstairs in the traditional way. He says he is installing 4 separate 4"x8" RA on each of the 4 upstairs bedrooms. He is also proposing re-tasking the existing 25x25 fed via 18" flex hose to the downstairs 5 ton AC so that the downstairs is fed via 2 25"x25" grills each connected to separate 18" flex hoses which would be connected to the 5 ton plenum.


Does this sound right to you pros?

[cartercrew]

According to my duct calculator, 4 4x8 registers won't move enough air for 3.5 tons. They. We'd to be 10 x 10, at least. Other than that, the design sounds good.

[udarrell]

The Ruud provider is telling me I need to add RA for the downstairs. The way the house is built it is impractical to add another RA downstairs in the traditional way.
He is also proposing re-tasking the existing 25x25 fed via 18" flex hose to the downstairs 5 ton AC so that the downstairs is fed via two 25"x25" grills each connected to separate 18" flex hoses which would be connected to the 5 ton plenum.
Both of those two Return Air grilles need to be filter grilles, using low pressure drop media type filters in each.

Then, there are no other filters used. That ought to do a fair job taking care of the RA flow needs. I compliment the Ruud provider for exposing that RA airflow requirement.