I think our plan right now is to have 90% of the insulation work done (everything but the attic floor), have another blower door test, and design the geo system off of those results. I believe that will give us a better sense of our home's energy efficiency truth.

One point I've been meaning to make - as an HVAC guy I want to be last in after insulation guys so they don't stomp all over my pretty ducts.

There is something to be said for buring the ducts in loose insulation, though.

Thanks engineer--of course the insulation guys didn't want HVAC people moving around all their pretty insulation to put in the pretty ducts ;-)...

In that respect, I suppose it doesn't really matter anymore who goes first, but at this point I think it might be harder to tighten the house to meet the geo capabilities than design the geo around the home's shortcomings.

I really appreciate everyone's assistance--it has been an education!

Two units are needed to avoid stratification? That's news to me. A single unit can handle up to 3 floors with proper zoning and duct sizing.

Let me first remove both feet from my mouth. Much better...

I saw retrofit 4000 square feet - two floors and thinking it's in coldville, I suggested 5 tons isn't enough. Only experience tells me that - but without a well done Manual J to confirm I'll just slink away into the sunset.
Note to engineer - got burned a few years ago with zone damping and one system trying to do too much. So, I'm always nervous getting over 2500 sq feet and trying to make do with one system and some damping. Hey, that's just me. However, the clients understand it costs more with an additional piece of equipment but they seem to be happier overall. That's very important to us. Comfort AND saving.

The reason I suggested they check with a DX guy is just so they have a basis of comparison in technologies. Experience trumps technology

Paul
TotalGreenUS.com
"We Do DX"

My feet have been there too.

We build tight homes and routinely get 1200-1500 SF per ton, so sometimes there isn't enough load for two units - must zone in order to spread a single system across 2 floors. I agree it can get hairy with overly small zones and the Copeland Ultratech 67% / 100% split - It would simplify my life if the split were 50-100.