tommy,
you talk about a LOT of things!
so your ducts are ductboard with 2 flex ducts?
ductboard is rigid fiberglass insulation board with
foil surface facing into the attic, flex is flexible
duct with foil insulation jacket.
1" ductboard is R-4.2 (just fyi)
the first thing I would look at is how is this duct system
sealed..duct tape..foil tape..mastic seal?
duct tape fails..doesnt take long in extreme attic temps,
foil tapes (unless mastic tapes) also fail quickly.
tapes don't adhere to dirty or wet surfaces, although they may look to be intact when the system is running you will be able to feel air escaping from these areas. sealing with a paint on mastic or cleaning and drying surfaces and sealing with a mastic tape is the better, longer lasting option. you can buy mastics at hvac supply stores.
areas of leakage on duct board would be areas where duct board sections connect, and each supply duct. flex would
be where it attaches to ductboard plenum.
these areas should be sealed with a paint on mastic sealant.

the other area of duct leakage is the supply box. if you feel around the supply boxes in the attic, they should sit evenly without gaps on the attic floor. lots of times the side attached to the ceiling joist makes a snug fit, but the opposite side (not attached to anything) will raise up when supply grills are installed. I use Hardcast mastic
tape to seal these areas from inside the house by
removing supply grills.

heat is an issue here also, today it is 92 degrees outside and RH is 87%. it isn't a bad thing that your unit runs alot when temps are so high. shortcycling, unit running 10 minutes on and 10 minutes off adds to cost of utilities, does not remove humidity and wears out equipment sooner.
You may want to think about upgrading to a higher SEER
heat pump, 10 SEER is not very efficient and is no longer
mfg'd because of inefficiency and cost of operation.
Federal tax credits can help to offset costs.

in adding more insulation to the attic...did you use layers of unfaced insulation?? the paper backing (vapor barrier) causes condensation between vapor barriers..this can cause more harm than good.

under the house the insulation should be in contact with the underside of the flooring, or condensation occurs between the gap between the underside of the floor and the insulation.

I'm not sure what you mean by double bubble wood siding for your walls... foil bubble foil wraps are not good insulators, and in our hot humid climate vapor barrers are to the exterior of the walls. cold climates have vapor barriers to the interior, but here promotes mold growth.
If you are insulating the exterior of your walls, a foam sheathing board with all seams taped is the best option.
to upgrade the insulation from R-13 in the walls to R-15
is a minimal cost and would be of benefit to you.
if you are not working from the exterior to the interior
..well..enough for now..that can be discussed later.
Like the attic ventilation...not enough info!

for your windows in your home, adding a piece of glass to
the screens really isn't your best improvement. check HD and Lowe's for Gila brand window tint. these will reduce
heat gain, whereas two panes of glass that are not insulated glass units will trap heat between the panes of glass.

I understand perfectly about being 57 and this being the last big undertaking..I'm 48 and just getting too stiff for some of this stuff!

That you are happy with a $300 plus utility cost just blows me away! My last utility bill was $70.00
my little house is about 950 sq ft full sun, just
plantings in the yard to block west sun from the windows.
when I first bought this house my utility bill
was $275 - $300 a month. Knowing where and how
to correctly address specific issues in the house
makes a lot of difference!
You can get help specific to your home that will
make all this time, effort and money spent worthwhile.
visit
http://www.natresnet.org/directory/raters.aspx
to locate an energy rater in your state.

I was just asking about ducts. Everything I have is coming out for a new system. The ducts I have now what I trying to figure out or the question. I just rambled on about my repairs. No I am not happy about a 300$ electric bill.

Back to the ducts distribution system. From your post I learned they are ductboard . The seal used is the mastic. Ductboard runs to all vent openings in a U shaped distribution manifold larges size duct bottom of the U. AC system input center of the bottom of that U . The entire U stands on about 1 foot legs (vertical duct) of ductboard The AC split system was first installed in this house over 25 years ago. The compressor/condenser was changed 10 years ago with a seer10 ($1400.00 total installed in 1999)its condenser fan failed and was replaced 2 years ago (both units Rheem). Air handling fan was changed one time in that period and the same natural gas furnace is still up there. Its working pretty well for such an old AC system. So the duct system came with the original AC. This system will be replaced with SEER 16.

.. Each 1 foot duct is a mastic seal on the attic side of the pine shiplap ceiling board . This manifold mainly hangs from the rafters for support . Each 1 foot run supplies 1 air register. (This house has ship-lap interior pine siding in each room when built it had gauze and wallpaper for interior walls 1937 construction. All interior walls are now drywall nailed on the original interior shiplap.) 2 exceptions are the 8 foot flex run which use the metal supply boxes. These locations are where the roof meets the side wall. My guess is they cut a hole from inside the house slid a flex duct with the air box attached through the hole and attached to the distribution duct.
Early summer I started some attic work and started inspecting the duct system. I inspected ever foot I know it sounds sick but I hand washed the duct looking for leaks. It looks pretty much perfect. I replaced each of flex duct runs due to the outside jacket was deteriorating. As I paint the rooms I remove the register and reseal the air vent area from inside the house.

I installed the faced insulation attic and under the house and in the walls. I am removing enough wooden siding (which are 6 inch pine siding each board has 2 humps or bubbles run horizontally the original 1937 this is where I use the term double bubble siding which is probably some local slang term). In the walls from outside the house I am installing the R5 next to the interior wall then a layer of backed R13 of a combine total of R18 then the siding goes up. Got a case of calk foam and such to sealing the walls.

Thanks for you answer the great amount of time in answering .

Sorry to hijack the thread, but which Hardcast product is recommended for sealing supply boxes, as mentioned by energy rater la? The website has a lot of products shown. Thanks.

To save typing, I used this for another 2-ton system on this forum.
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Normally, we would use 6 or 7" branch ducts for a 2-ton system, depending on the number of branch runs, to keep velocities low enough.

However, he had 8-runs; Eight (8) supply branch runs which means: 24000 / 8-runs= 3000-BTUH per duct.

FIGURING ROOM CFM - DUCT SIZES

Quick method: The heat gain and Btu/hr of cooling is done for each room.

At 400-CFM per/ton of cooling, 12,000-BTUH / 400-cfm = 30-BTUH for each (CFM) Cubic Foot per Minute of Airflow.

Then Select Supply duct size by CFM, velocity, & optimal Supply Air *(FR) Friction Rate.

A Room requires 3000-Btu/hr divided / by 30 equals 100-CFM, or around a 6" dia. RD metal duct.

He had Eight runs; 8 X's 3000-BTUH each run= 24000-BTUH.

Maybe a 4" to a small bathroom, etc.

You have to balance out the duct system to meet the BTUH heat-gain in each room.

Do not make your decisions solely on my information, work with your locals! - udarrell

Here in Austin my last electric bill was $99 for July.
Slightly more sq ft than the OP but my windows
were replaced along with all the other upgrades
he already mentioned. Windows are the key I believe.

udarrell_2007

Overview of Duct Sizing

Thank you so much For your example and link. I been reading and studying on your site for hours now.
I am seeing a lot of areas for improvement for my home . From reading there I really understand now why my suspicions about AC companies and such were well warranted . I actually saw a example Last month. I watched a company install a unit for second floor addition to the house directly across the street ( brought a 1ksf home to approx 1800k over 7 month project) I watched this highly trained technician vent a cloud of R-22 / lubricant the size of the house. At first I thought it was a fire. I watched as he did it the second times so wasn't a mistake someone must have overcharged it.
I am reading every page and all the links just getting started but sill not seeing what high end R value is for a duct material