Have you checked out heat pumps ?

For that price, I'd expect to see two mid level (high efficiency, 2 stage) systems - one for the first floor and one for the second floor. Of course, it all depends on the complexity of the ductwork.

Thanks - for all the input so far. We have a boiler w/ radiator heat that works quite well and lived in a house in the past w/ forced hot air heating. We much prefer the radiator heat.

Obviously , I'm not an HVAC person, but I don't see the duct work as being that complex. There is a full attic that one or two airhandlers could be placed in. The attic square footage perimeter mirrors the two floors below it and as I said, demolition is taking everything down to the studs (including ceilings). Nothing unusual to aircondition - bedrooms, bathrooms, and a family/media room. All flat ceilings w/o vaults etc.

Be careful inferring the cost of anything in new construction these days based on what you or someone else paid--even for an identical scope of work-- a year or more ago. Steel, aluminum and copper prices are all up about 1/3 this year. PVC pipe is up. Insulation is up, too, particularly foam insulation. Throw in the increases in the cost of fuel, vehicles, health insurance, worker's compensation insurance, labor price increases... well, you get the point.

In terms of the system design i'm also wondering if it makes more sense to have two units with each floor having their own dedicated one though I know there are pluses and minuses to both approaches. I know from reading these forums that if we do go w/ a single unit that is zoned the compressor and air handler should both be two-stage or variable units and that a bypass duct system shouldn't be used. Is there anything else I should be asking or looking out for?

HVAC zoning is primarily used when:

1. The structure has an existing single HVAC system in a home with two or more levels or an expansive one level. The existing system is still operable, in this scenario.
2. The structure does not have the room for a second HVAC system.

If a system is still operable, adding another system to zone a structure will then "over size" the conditioning needed for the structure. So to do it right you would need to size the 2 systems appropriately for each zone they condition.

Duct work: When zoning via a single HVAC system there are a myriad of ways in which to accomplish it. I believe much of this in my experience -- which is living in a hot humid climate in which air conditioning is required 9-10 months of the year. Given that, much more complicated for my climate, especially which these systems also operate heating as well as cooling.

So if you live in a more moderate climate that uses air conditioning much less? you *may* have less trouble... unless of course you're facing an extensive heat wave. Much less means 3 months, maybe part of 4 months. (You mention Philadelphia, so your concerns are much different than someone in my neck of the woods in Katy, Texas)

Your heating is an entirely different system (radiator)... so the zoning for AC is only going to come into play when operating the AC.

Air conditioning is part mechanical removal of heat, and part movement of air. Air flow requirements are typically around 400 CFM of air per ton. While you can modify this some I personally would go no lower than 350 CFM per ton.

What kind of equipment:

If you choose single stage AC equipment, there is no efficiency gain when zoning. It's more about putting conditioned air where you want it. It's more about comfort in the zone or part of the house your in.

Example: a 5 ton single stage air conditioner cooling 1 floor of a home is doing the same amount of work, if it were cooling the whole house.

Example 2: a 5 ton 2 speed air conditioner can run in 1st stage most of the time, it might save you some coin, but not much. 1st stage is 70% of capacity of the machine. In a moderate climate 3 months need, you may break even depending on a host of various factors.

Example 3: a 5 ton inverter will vary ramp up and down as the "load" dictates. So depending on climate again, how much you run it vs what you pay in utility costs can make this the better option. However, equipment costs are higher and repair costs will be higher as well. In zoning this option would be most efficient because ramping the compressor costs more and if you only have a single zone open?

Choosing 2 separate HVAC systems: if one breaks you have a back up. Repairing two HVAC systems costs more to maintain, repair and ultimately replace when that time comes.

HVAC zoning is complicated: The job I did that I talk about below... at least a couple different HVAC companies tried to repair it. (unsuccessfully)

I did a HVAC zoning redo earlier this year. I gave the option of including an inverter AC along with new HVAC zoning. The customer decided to reuse his existing single stage AC as it was still operable and not in that bad of shape yet. He was completely happy with the job even though he decided to keep existing equipment the same.

He was quoted $30,000 to fix this problem by more than one competitor. I also told him during the process that he could do the AC inverter later if he wanted to.

I service the Katy, Texas area.

"Example: a 5 ton single stage air conditioner cooling 1 floor of a home is doing the same amount of work, if it were cooling the whole house."

That statement might lead folks to an erroneous conclusion. The amount of "work" required (in the form of electrical energy consumed by the compressor motor, fan motor, and blower motor) is based on the cooling load. The cooling load of one level of a multi-level home is some fraction of the cooling load of the entire home. While a single-stage air conditioning system will operate at the same cooling rate when only one level (or one zone) is being conditioned, the run times will be shorter, thus the amount of work is not the same as it would be for conditioning the entire home.

The problem with zoning single-stage air conditioning systems is the lack of turndown capability which can result in short cycling and inadequate dehumidification. In the case of the OP's home (and the OP seems to be aware of the need for a multi-stage, v/s system if it is zoned,) the concern is whether the turndown capability of the proposed system will comfortably condition the second floor-- which has conditioned living spaces both above and below it. That requires comparison of the manual J calculations for the 2nd floor level with the turndown capability of the particular system proposed. A chat with the HVAC system designer is in order.

While a single-stage air conditioning system will operate at the same cooling rate when only one level (or one zone) is being conditioned, the run times will be shorter, thus the amount of work is not the same as it would be for conditioning the entire home.

I performed the experiment on my house, with a single beater 14 SEER AC prior to installing my Inverter AC in 2019. I live in a climate that uses air conditioning 9-10 months a year.

There is no significant savings that I can see using a single speed AC... I paid $146 for cooler month, versus $192 for hotter month. My zone system is zoned for 4 separate zones. System is 4 ton capacity.

The AC inverter cut this essentially in half. You can view the comparisons here on my website.

Okay, I'll try again.

The total amount of work required to cool a two-story home is the sum total of the work to cool the first floor and the work required to cool the 2nd floor. So a zoned air conditioner doesn't require the same amount of work to cool either level as it does to condition the entire home. With a fixed-speed system, the cooling rate is the same whether it's conditioning one or two levels, but the run times are different for cooling only a single level.

The addition of zoning to a single-stage system would not be expected to significantly alter the energy bill, but rather to enhance occupant comfort.

I thank the experts for their continued input - with each addition to the thread, I and hopefully others who read this become more educated

The addition of zoning to a single-stage system would not be expected to significantly alter the energy bill, but rather to enhance occupant comfort.

Yes, Correct.

There are many people with doubts, I am in the unique position to offer solutions / include proof what works / what works better / what you may or may not expect in way of pay back for those efforts.

To go into this further: Just note this info in picture below pertains to Katy, Texas area. Click to enlarge if necessary.

The $105 cross section from 4 ton to 14 SEER in the piture above shows what you can expect in terms of operational costs when all other things align... meaning set point is 75 indoors, 95 outdoors, your cost per KWH in this example is 9.7 cents per KWH.

Deviation: I primarily operate two zones in a 4 zone system, set points at the time were 76 during the day / 74 at night.

Typically without any HVAC use for this house my electric bill is around $30-40 a month.

The chart above includes higher SEER operational targets. The AC inverter is rated at 18 SEER, but due to the nature of how it operates & the zone system higher operational savings can be achieved, especially in lower than 95F OAT. (outdoor ambient temperature)

I service the Katy, Texas area.

What are the sizes of each floor of the house? Is the air handler located in the basement? Will you be upgrading the insulation on exterior walls or attic?

I am skeptical whether a house in the Philadelphia area needs a 5 ton AC especially if you improving insulation and windows. The proper way to do this is to do a cooling load calculation with the renovations. If you actually required more than 4.5 tons of cooling, then you want to make sure the duct work is properly sized.

Many HVAC contractors do a poor job when it comes to zoning. Your situation may be a little different because new duct work is being installed. Most general contractors are not skilled in HVAC design. Hopefully he will use someone that is competent and not the lowest bidders.

I suggest you get a quote for separate systems for the first and second floors. It will cost more than a zoned system, but it may be worth it. In my opinion two separate systems in a 2-story home can provide cost savings in addition to better comfort.

Each floor is approx 1750 square feet. The airhandlers will be in unconditioned space in the attic

@Shadow's Owner,

You need to speak with your HVAC contractor about the calculated cooling loads for each level of your home and discuss the alternative of two separate units versus a single unit with zoning.

Is there any options of moving one of the air handlers out of the attic? Unconditioned attics are the worst location for HVAC equipment and duct work. It is worth investigating if the equipment could be moved to a conditioned space.

I live in central NJ in a house of about the same size. The cooling load for the first floor is about 1.8 tons, and the second floor is 2.4 tons. This will give you an idea of what to expect if you can find a HVAC contractor who will do a proper cooling load calculation. Proper here means measuring all rooms and windows, and entering the information for insulation values and orientation of the house into a software program. A calculation based solely on the area of the house is not the way to do it. It tends to create over sized loads and equipment.