I've had three different companies give bids for my house, Stan's for a Carrier system, Service Wizard for Trane and Green Leaf for Trane. I've been told based of my square footage, approximately 3100 sq ft of which 1950 is downstairs and the remainder is upstairs, that my system is slightly under sized at a 3 ton for downstairs and 2 ton for upstairs. Also, the supply plenums need to be redone to accommodate the larger tonnage and I need an additional supply run on the upstairs unit because it's only flowing 500 CFM, which isn't enough even for a 2 ton unit. Do these bids seem reasonable?

Stan's:
Carrier 16 Seer two stage 3 ton and 2 ton:. $23,250
Carrier 16 Seer single stage 3 ton and 2 ton: $16,900

Service Wizard:
Trane XR16 16 Seer single stage 3 ton and 2 ton with adding additional supply run: $14,600
Trane XR16 16 Seer single stage 3.5 ton and 2
5 ton, rebuilt plenums to account for larger tonnage and additional supply run for additionally needed CFM for upstairs unit: $17,400
Trane XR 17 16 Seer two stage 4 ton and 3 ton, rebuilt plenums to account for larger tonnage and additional supply run for additionally needed CFM for upstairs unit: $24,700

Green Leaf:
Trane XR16 16 Seer single stage 3 and 2 ton, no rebuilt plenums or additional supply run for upstairs unit: $16,300
Trane XR17 16 Seer two stage 3 and 2 ton, no rebuilt plenums or additional supply run for upstairs unit: $17,300

All bids include complete inside and outside units, gas furnace, and typical installation.

Not sure what to think about up sizing the tonnage because I'd be concerned about short cycling. Also, the guy from Service Wizard didn't seem to think the 2 stage was really worth it. I'm awaiting an updated bid from Green Leaf to see what they think about rebuilding the supply plenums and adding an additional supply run for the upstairs unit to get to the needed 1,000 CFM, up from the current 500 CFM. TIA

Carriers since the 80s always costs us 50-70% in repairs compared to first-cost, even when sports buddies put them in for us. Never again. Heat pumps "single stage" (a waste of money from the get-go), Aggieland.

TRANE
Trane is the best equipment, now don't screw that up with cheap labor install.
2-stage may get you through the winter OK = the very LEAST of the stages to buy if you're selling house in 5 years

VARIABLE STAGE
Variable is the only pay-me-back in energy savings path, regardless of cost.
Trane saves on repairs with skilled labor.
When in doubt, bump up the tonnage 1/2T for August + every 20 hot guests EAT up a full ton when inside + steam showers/cooking and high-wattage appliances/TV/computer/etc.

Now 9 months old variable 4ton 18seer Heat Pump was $16k buddy company's installed no duct-work

INSULATE & LEAKS
Ask if they will insulate the ducts & if so, double the R-values = money coming back to you month-month
All ducts leak ... from coat closet amount when new ... to as much as Bedroom amount when system gets replaced ... so plug any leaks when insulating.

MECH.ENG
All our projects that could afford a licensed Mech.Eng proved this rule of thumb
475sf/Ton
525sf/Ton IF it has a conditioned/insulated floor above it
This trumps all power company self-serving rebates/incentives that can force Owner discomfort up to 750sf/Ton?!?!? Caveat Emptor!

BOTTOM LINE
What I would do
XV20i TruComfort Variable Speed
3T down, 2T up, taking a risk both are 1/2T undersized but making up for that with double insulated ducts, even radiant barrier sheets topping them + variable does so much more work with not so much energy $$$$$