Just wanted to mention what contractor plans to do with the duct work. If we stick with existing Goodman AC & furance he will raise it off the attic floor. Either option he will redo the plenum and the main trunk lines(3). Most existing duct work that is supplying the rooms he feels is ok, so it stays. However I know it is all R6 not R8. Will also put dampers in some supply lines, add an a/c auto shut off, add bypass (one does not exist now), add 1-2 new returns. He make sure zones are still working properly after duct work changes (they are EMC? zone controllers and an Aprilaire box).

This is from my memory I have nothing in writing about what he will do to the duct work, just remembering what he said. I will get something in writing if I move forward.

To me this is the biggest part of the quote that seems out of line ($4200 seems high almost as high as being able purchase brand new duct work job), but hey I'm not the one in the hot attic working all day?!?

I agree $4200 sounds like a lot of money to fix your current duct work. Do you have another quote to compare?

I don't understand why you need to purchase an air handler with the new AC. Why are not not using the blower of the current furnace? Am I missing something?

I would think the 3 ton condenser is undersized for your house and climate. The Manual J calculation makes sense.

You are trying to keep costs down, then why are you getting a quote for a heat pump? You have a relatively new furnace and mild winters. I am not sure this is the best use of the funds.

It does not seem right you could be spending a lot of money on a new duct work and AC, and then have to install a mini-split for the bonus room. I would rather get a properly sized condenser with zoning to handle the bonus room.

You have a challenging problem. I suggest you speak to some more contractors to get more ideas and better prices.

The contractor was in the attic looked at the blower and said it didn't "match" with the new AC system, hence the recommendation for the new air handler. Not exactly sure what that means but I think he's being truthful.

You've got me wondering now if I should just replace the AC unit, redo duct work and keep everything else (blower, furance).

Assuming that Manual J is correct (and based on your complaint) you need more cooling. Going the route of new central zoned unit, duct work changes etc. is the expensive fix especially with a relatively new unit already in place. By just buying a mini split heat pump and minor duct modifications you should be able to isolate the bonus room with the mini split and let the air that was going to that room be redistributed to the other rooms. Bonus room is 216 s.f. Not knowing the number of windows or orientation of the bonus room among other things makes it harder to recommend mini split size but as mini splits can "throttle down" the compressor and air flow it's less of a problem if you over sized the unit...I live in Columbia, SC so I'm familiar with the climate. I have a 15,000 btu (1.25 tons) mini split heat pump in my 400 s.f. glassed in sun porch (east orientation so the heating load isn't as much) which does a nice job handling heating and cooling. Even with a south/west orientation I'd think that 21,000 btu might be more than you need for your bonus room.

I live in columbia, sc too, small world. Mine if I ask if you have a local HVAC person you really recommend?

rooms in attics are always hard to cool in hot humid climates.
the price to slightly modify ducts is high.

I'd look into putting open cell foam on roofline
which will put upstairs room & duct work inside
a conditioned space. this will stop heat gain
in ducts, upstairs room & the rest of the house.

once this is done then mastic seal ducts..you can
diy..and see if hvac system keeps up.
if not change hvac.

the biggest improvement for uncomfortable homes
with rooms in attic space is to foam the roofline.

check on prices before you let people tell you
how long the payback will be, as prices vary.
also keep in mind that open cell is at best
R4 per inch. 3" isn't doing much. better to
go with 6" and cover the face of 2x rafters.
it doesn't double the cost as any upcharge
is just product, not set up.

get several foam bids, and several hvac bids.

best of luck.

If there's a mini split involved in your solution I strongly recommend that you only use a HVAC contractor who's got extensive experience installing them. I personally would recommend a Japanese brand. Of the Japanese units in our area I typically see Mitsubishi, Fujitsu and Daiken units. I have a Fujitsu but in work related settings (I'm an owners rep construction coordinator) I see a lot of Mitsubishi and Daiken brands.

Not sure what side of town your on (I'm near the Lake Murray Dam) Some potential HVAC companies might be Cassell Brothers, Duncan, Shealy, Pardees. If your interested in the Fujitsu you might try Lexington Heating and Air as he's listed on the Fujitsu site as their #1 recommended installer and he did mine. I'm sure there's plenty of other very capable companies so have a number of them give you quotes. My experience was that for quotes on 15,000-18,000 btu mini split heat pumps that the total installed price quoted was between $2800 and $3600...so your quote of $3400 for a 21,000 unit seems in line.