What to consider in a central air install?

yeah, but that’s why I think the smaller 3 ton is an even better choice if zoning is selected. But you are right, two separate units would be best. Given the constraints on this install (ductwork already installed) a zoned 3 ton system may be the best choice. I’d be interested in how the zoning will work though, with the duct already in place. I’d guess some motorized dampers.

Thanks for the help—this has been great for peace of mind.

I spent about an hour on the phone with Lennox corporate asking a slew of questions about the units under consideration. They guided me to the Air Conditioning, Heating and Refrigeration Institute’s web page to get (ostensibly objective) product ratings (SEER/EER/cost to run). It takes both the condenser and the air handler as inputs.

We’re looking at either: AHRI Ref #3291687 or Ref# 3665362 (the results don’t have their own URLs).

The first is the more expensive package ($13,000 + $3,000 zoning package). The compressor is a two-stage unit, and the air handler is variable speed. The second is not too far away in cost ($11,800 + $2,200 zoning kit). Its compressor is straightforward (not 2 stage) and the air handler doesn’t have the variable speed motor.

Of course, things aren’t easy. According to the ACHRI ratings, the first package’s ratings are 16 SEER; 11.5 EER; and total annual cost estimate is $255. The second package (the cheaper, less bell and whistley package) is rated at 16 SEER** 13 EER**; with a total annual cost estimate of $255—a marginally better EER rating and the same average estimated cost.

But… but…* 2 stage*!* Variable speed air handler*! Aren’t these primarily related to energy savings? The variable speed fan might make a difference if we were using the unit for heating, but that’s not an issue in this case. If no one looks at the electric bills, will the two systems be fairly indistinguishable from each other? Or is this like zones–something with both efficiency and comfort factors?

[On a side note, installation includes hanging the unit from the rafters (instead of seating it on the joists), a piping directly to the outside (not to the gutters), and seated in a drip pan with a cut-off float valve in case something goes wrong.

The Harmony III zoning option includes zone dampers, zoning board, low voltage wiring and a discharge air sensor. ]

We’ve got a 3 zone forced hot air/AC house, and it uses motorized dampers. Definitely worth the money - one zone is far more exposed to the exterior than the rest of the house, and is thermally isolated from it as well, so it cycles more frequently than the other 2 zones.

My only suggestion on that is make sure the motors on the dampers are accessible - don’t let them put a pipe directly underneath it or put it above a drywall ceiling. We’ve had one go bad so far, and it would have been a much uglier job if it hadn’t been easy to get to.

I think the 2 stage unit with variable speed unit might address Snnipe 70E’s concerns, but again may very well depend on the configuration of the existing ductwork.

The two stage compressor and variable speed fan allows the unit to run properly at a lower capacity when only one zone is calling for cooling, and run at full capacity when both zones need cooling. So once again, these items are related to energy savings but they also have value in providing comfort.

At this point, it sounds to me that you have a very competent contractor, and would tend to go with their recommendation. However, these systems are more complex so you also want to talk to them about the warranty and required maintenance - that may play in your decision.

I do not work on Residential, except mine, but everything I have heard about the two stage compressors with variable speed fans has been good.

In my case the ral problem was or is return air. I have poor return air on the 2nd story and no way of really improving it easly.

Thank you! Thank you! Thank you! Thank you! Thank you!

So we signed a contract a week ago; they’re coming in today to do the pre-install site inspection (I have no idea what that will entail—they’re not here yet).

We ended up going with: [ul]
[li]A Lennox 3-ton two-stage condenser; [/li][li]Lennox variable speed air handler suspended from the rafters in the attic (on a drip pan, with float valve, etc.); [/li][li]Harmony III zoning package; [/li][li]MERV 16 air filter system; [/li][li] Hard start kit on the compressor; and [/li][li]Installation of two additional return air grilles.[/ul][/li]
There are several other things not written in that list that affect it, such as the thermostats, that “all line set connection to be razed and vacuumed,” and that they’re be doing duct performance tests with a “calibrated draft hood” during installation to ensure the load is properly balanced.

The company we went with was a bit more expensive in some ways, but they offered the most detail when doing the estimate (both in taking measurements and describing what’s included) and answered all of the questions and concerns we brought up—again, thanks for helping us become informed consumers. They also had the right mix of technologies that seem to fit what we’re looking for/need, and great references.

Total cost was initially about $16,000. I called Lennox and they set us up with a $500 rebate, and the contractor brought his price down by another $500 so we’re right at $15,000 complete.

Installation is set for early May, and we’ll see how the process goes—then we’ll see how the comfort levels run in the summer. If anyone is in the Hudson Valley region (NY) and is interested, PM me and I’ll share the contractor’s details.

Again, thanks!!!