What size living area is each zone?

IMO

Tigerdunes: zoning was suggested in the first floor, the 2 zones are 500 sqft and 1600 sqft.
What is the difference between variable speed and multi speed blower btw ? American standard lists most of its furnaces as multi speed and a couple as variable speed. Are the multiple speeds in a multi speed controlled by load/ thermostat or is manually set at the time of installation.
Thanks Sri

Has the contractor done a load calculation? The house must be very big in order to justify 8 tons of cooling. Most homes don't have sufficient duct work to support a 5 ton unit. The contractor needs to verify you have the duct work to support all the required air flow.

I also would want a load calc for each zone.

Again, what size is the living space for the three ton system and the 5 ton system?

Variable speed furnaces are multi stage heating with ramp up and ramp down blower profile. Biggest benefit is improved dehumidification in AC cooling mode. For best performance and to achieve VS furnace operational capability, they should have a true two stage thermostat. The model quoted is incorrect.

The sgl stage furnace has fixed speeds that are adjustable. The model quoted has a high efficient blower but is not var speed. A good furnace though depending on application.

IMO

The contractor that I quoted performed the most comprehensive load calculation . Again, I am no expert but, a layout of the house and each room was measured wrt orientation, sqft, size of duct, window sizes and whether it was interior or exterior wall. All of this was loaded up in a laptop and the output was " you have the right equipment".
The living area on the first floor is 2100 sqft and 2 nd floor is 1700 sqft. I am not sure if the duct work was " checked" but it was definitely given an all clear. The only insufficient duct was the game room duct, where replacement was suggested.
I think I will go ahead based on tiger dunes explanation and spring for the variable speed blower. What in your opinion would be a good thermostat for this setup ?
How would I request a load calc copy? Is it a software file or just numbers written down ?

The floor areas you have quoted and the size of the units make no sense. Are you sure these numbers are correct?

Get a print out of the load calcuation. It should state the number of BTUs for heating and cooling. Get the name of the software being used. I am doubtful of a Manual J calculation software application which prints out "you have the right equipment".

Are you going to get any other quotes? You should get at least three proposals for a project of this size.

The load calc should be printed out on the software letterhead both cooling and heating with design temperatures inside and out for each zone. The best software shows the load calc for each room in the zone.

Like the above post, I question the sizing particularly for the 5 ton zone.

If going var speed furnace for each system, I would want HW VP IAQ thermostat latest edition.

IMO

mike_home: I was implying that most contractors agreed that i have the right equipment and not that the software read "you have the right equipment" ... lol. I did receive more than 3 bids/proposals. The cost of the equipment was very similar in all 5/6 bids. The only difference was in the cost of the add-ons like "accu-clean" etc. The reason i was tending to choose the quoted contractor was the warranty aspect and lower cost of add-on equipment.

mike_home/tigerdunes: I will try and get my hands on the load calculations and share with you guys if/when available.

tigerdunes: I will inquire about your suggested thermostat wrt prices. Are there any more models you would like to recommend? North texans have been constantly bombarded with advertisements for "NEST - Learning Thermostat". what are your opinions on those? They seem super pricey, especially if i have to buy 3 of them :) I am surprised that the contractor will provide a thermostat that will not be able to utilize all the features of the equipment. Is this standard practice in this industry ?

Thanks a ton for all the responses.
Sri

"I am surprised that the contractor will provide a thermostat that will not be able to utilize all the features of the equipment. Is this standard practice in this industry ?"

It happens more than it should. There is no need to have a two stage furnace with the timer on the control board handling the staging of the heating. A pure waste. And why does this happen? Because many dealers take this shortcut to keep pricing down on unsuspecting homeowners. A true two stg thermostat will run in low stage and never go to high stage unless demand requires it.

The HW VP IAQ is a tried and true two stage thermostat that also has dehumidify on demand feature for AC cooling. This could be helpful for your N Tex location. There are other models like the HW VP IAQ. I just think this is the best for the money.

IMO