Yes Natural Gas Furnace for Heating along with the AC condenser. I have read up a lot on zoning, it seems to me like there are not a lot of installers in the industry that really know how to set them up properly. There also is a lot of negative information on zoning as it relates to the troubles a by-pass can cause to your systems efficiency. That is why I was leaning towards the two unit system, however need to figure out the proper size for each level. I know the best thing to run is a Manual J on the place however as a starting point what is the general rule based on square footage in determining the tonnage and BTU for a heating and cooling system? That along with how does the rising of hot air and the dropping of cool air determine the size you would go with? Any help would be appreciated.

Jt Some questions please. What is your location? What size home living area? What size furnace and eff are you replacing? What size AC are you replacing? I would like to know the exact mdl number evap coil for each quote. What thermostat is proposed for the Carrier quote? That is a big difference between the 96% eff Carrier furnace and the 80% eff Trane furnace-both 60 K input. That would be about 56 KBTUs output on the Carrier and about 48 KBTUs on the Trane. Not insignificant. I don't care for some shortcuts that homeowners make particularly on reusing linesets and using existing thermostats that shortchange a nice furnace's operational capability. Post back with the info requested. IMO

WHAT IS A HIGH LIMIT SWITCH? https://www.newcentralairconditioner.com/ The high limit switch in your gas furnace is a small part with two very important jobs. This switch plays a role in the normal operation of your furnace. Turning the fan motor on and off is the high limit switch’s main job. This is the role it plays in every cycle of your furnace’s normal operation. But that’s not the only thing that the high limit switch does. It’s also safety device that helps prevent your furnace from overheating. The high limit switch consists of a long temperature-sensing probe attached to a metal mounting plate. From the mounting plate, the switch is wired to the blower fan motor and to the gas valve. The switch is generally located just past the heat exchanger. This is so that it can detect the temperature of the supply air. In other words, the air that’s about to be blown into your home.

The biggest problem with HVAC zone systems is knowing when to choose it as a solution and when not to. Some HVAC companies it's about "sell, sell, sell" whether or not it works... there's more money in "sell, sell, sell" --- when it's only about money? So does the comment above mean I do it for free? No. If you think that you are reading things that aren't there. New construction? best to choose separate systems 9 times out of 10. In order for a zone system to work, you have to know what you are doing. Most HVAC companies staff (the techs they send you) are 20-30 year olds. How much practical experience could they possible have? It's best for HVAC zone systems to be an elegant solution. A HVAC zone system is a tool in the tool bag. Not all homes are suitable for zone systems. Some homes there is no other way, and in some cases complications to those problems will make an HVAC zone system design possibly more prone to problems. You have a problem now, do you want more problems. These decisions among others are decided "in person" --- so considering that becareful what information you decide upon from the internet. Just because it's here doesn't necessarily mean it's true. That said: Depending on equipment level chosen, how many different floors you have in your structure, how much room you have available... will all be factors that make you decide one way or another. From there it's in your best interest to pick a contractor that is skilled: especially when it comes to HVAC zone systems. (there's a lot of garbage out there.) (click to enlarge if necessary) I service the Katy, Texas area.