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What was the pressure drop from day 1 to day 365 ? There is always an exception to the rule.

Is it an inverter system or the traditionnal on/off type ? Do turn the unit off sometimes after running A/C or do you leave it on pretty much the whole time ?

There are several threads already regarding A/C sizing, I’m thinking a sticky listing the necessary information needed to answer that kinda question would be nice.. So, again, the basics are : - dimensions and orientation of conditionned area - insulation R values for floor, walls and ceiling...

Units have specific specs for lineset elevations, lenghts, etc.

Yeah that’s pretty much it. However I just realized I missed the 2nd story attic space... should not make a huge difference though.

The drain needs gravity, or a pump!

This is the quick load calc I did with the data you provided. Design indoor cooling temp 78, indoor heating temp 55. Do you plan on heating only with the heat pump(s) ?

Before we can help you, we need the following: - zip code or city/state - insulation R-value for slab, walls, ceiling - type of windows and doors and their size - front door orientation - what temperature do you want to maintain inside during cooling and heating seasons - do you plan on opening...

« Up to 1 year. » Considering most ducts are improper to begin with and already put a burden on the fan motor, a dirty filter won’t help. It’s common sense depending on usage and environment but twice a year is a starting point IMO.

No filter is a yearly filter in a normal residential environnement.

I had missed that ! :yikes: Hopefully they're good filters !

I would bet you are waaaaaay oversized, 1st. 2nd, if the filter is clean, have the coil and ductwork checked. Test the fan motor too.

4300 sq ft per floor or 4300 sq ft total ? 8 tons of cooling is a lot. I mean, A LOT. Do you have flexible ducts ? If so, did you check to see if it was in good condition ?

Of course if the numbers are inaccurate the results will suffer... I can’t argue with that. The 2-ton quote in this case is almost double what OP really needs... even a 1.5-ton is ~35-40% oversized. Why 2.5-ton ?!?

How do you figure actually sizing a unit according to the cooling load will shorten the compressor’s life ? Oversized units are a pain.

Oh right i had missed that. A properly designed system will not cycle as such And I’ve never heard of a sizing a system based on problematic installation and neglected maintenance... Are you suggesting that short-cycling is the way to go ? That’s how you kill a system, not with the high...

R10 around the slab is possible and actually common around here, so why not ?

Well actually looking at his calc and specs we can figure out just about everything that's needed, considering what he put in is right. Fresh air intake + infitration is missing, but if it's a new building it should be at least average, hopefully better. 2-ton + 45k seems good. Did you ask...

How did you go about recovering refrigerant prior to replacing the indoor coil ?

If you dont plan on doing heavy (wood, metal, etc.) work in there and don't need the better filtration of a central ducted system, I would go ductless. 3 x 9k units on the east wall, evenly spaced across the wall lenght. If you want to get closer to the heating load, you could do 2 x 9k + 1 x...