Gas and Oil Home Heating Furnaces - A/C for a new home

We are in the process of building a new house with about 2000 square feet down and 1200 square feet up. My question is would it be less expensive to operate two 2.5 ton unit vs. one 5 ton unit for the downstairs? What are the advantages and disadvantages for one vs. two units?
Also, can anyone tell me if the Aprilaire Electronic Air Cleaner model # 5000 is worth the extra $300 over the Aprilaire High Efficiency Air Cleaner model # 2400?

Thanks,
Elmer

If it were my home, I'd have 1 unit for the entire home and use zone control dampers and zone thermostats. The actual tonnage needed for your home depends on many factors. A manual J heat calculation will size the equipment and the ductwork as well. IF the contractor is a competent one he will do the calcs and explain the results to you. If not, look around for one who will.

I would use 2 sep units, if one goes out you can live in the cool part of the house until the Monday to avoid OT charges.
Also few HVAC contractors can size/install untis for optimum comfort and termpature distribution even with a simple one story house.
Throw zoning into the deal and you will need a true professional to get it right for you.
If you know a really good HVAC company zoning is a good option.

zoning can work if installed properly but I prefer the 2 systems for your application
I know two excellent contractors that install zone systems and I still notice temperature variations in the two levels
zoning duct systems with dampers and stats for 3200sq ft should be done with exact load calculations and a master duct installer
It can be done if the right contractor is found

with the two systems, the upper and lower levels of your home are controlled by separate thermostats
just my preference
-
just be sure to request a load caluation whichever path you chose

For what you want I would go with the two units. We find it works a lot better than zone set ups even when they are put in the right way. Like the AC for up will want to run more than down.So why pay for a 5 ton AC to start ,look at the amp draw for start and run for this 5 ton and all you need is the little 2.5. Also with the 5 ton it will drop the temp fast and shut off while it didnt get a chance to do a good job and get the humidity out of the home for you. They did run a AC load check on this home for you didnt they?;) ED

As stated earlier, when one goes down, you have somewhere to go, instead of sweating like a pig, and at the mercy of "We can get there a week from next Friday"... Also with zone control you are still running a big unit to do a small space and lots of short cycling depending on demand, Most don't cool unless a minimum of two zones are calling. It might be different if the compressor had multistaging unloaders for the compressor/s. Go with two!

Thanks for all the replies. I want to make sure that you all understand my question. The house will be two stories, the first floor will be about 2000 and upstairs about 1200. My question is about the first floor ac unit. The builder is guessing on 5 tons down and 2.5 tons up. Should we go with one 5 ton for downstairs or go with two 2.5 tons units? The upstairs will be somewhere around 2.5 tons.

Ed, the AC contactor will take a look after the walls are up.


Any comments on air cleaners?

I seriously doubt the downstairs will need as much cooling per sq ft as the upstairs.
Sounds like a contractor using a "rule of dumb" for HVAC sizing !!

You said------------ he is guessing------------- 5 ton for down???????
And a new home! He should just take it off the prints and come up with the load. Boy have him run a heat load on it. You dont do it by the sq ft. Have a 4600 sq ft home in Mo. With 6 tons. Down here in Fl 3 ton will work most of the time for about 2000 sq ft home but its all in the load not the sq ft.;) ED

Even in a commercial rule of thumb of 1 cfm/sq ft divided by 400CFM/ton that would be 4 ton, and the residential is divided by 600 that would be 3.3 ton I think the 5ton sounds a bit extreme.
With new construction... try a heat load calculation and add 10%... even with a heat load calculations, they are generalizations but do give the best idea of exactly what is happening. I did one once and it came out to be about 5 ton, on one level but 3 tons were for cooling a sunroom with glass, top and sides all around,.... and single pane to boot!
:p

go with a single unit downstairs...just size it by a heat load calculation to make sure the size is right and a properly designed duct system.

I still like the single system. But, the contractors who can do it right are rare.

I doubt that the house needs more than 5 ton total. The calculations need to be done. Since most homes have open stairwells, a significant part of the heat from the lower floor rises up the stairwell and adds load to the upper floor (lowering the actual load on the lower floor).

For a 2-story home, I move about 1/3 of the calculated summertime load of the first floor and add it to the second floor.
Example: If I calculated load a 3-ton on first floor, and 2-ton on 2nd floor. I would install a 2-ton on the first floor and a 3-ton on the 2nd floor. This has worked well for over ten years in Arizona where we have a serious summer and a very mild winter.

For a frigid climate, I have no experience, but I think that I would do a 3-ton upstairs and down. (The larger unit downstairs would allow the energy saving heat pump to heat the downstairs even though a significant part of the heating rises up the stairwell and reduces the heating load for the upstairs unit.)

The single unit would reduce the installation and maintenance and repair costs for the life of the home. It would also easily shift the air as needed for both summer and winter use...MY preference. In reality, there aren't that many companies who will deliver comfort on a 2-story home...no matter what the strategy.
SAD but TRUE.