[energy_rater_La]

more info please.

1950's build, with jalosie windows...
what are the walls? concrete block exterior &
sheetrock to interior? can you describe them for us?

when you say insulation boards in attic...what type?
how much? only insulation boards or that plus some
other type of insulation? flat roof? or is there attic space?

jalosie windows are very leaky. using a plastic shrink wrap
over them would be your cheapest option to keep ambient
hot humid air out of house. this excessive infiltration
will have an effect on sizing & comfort, so eliminating the
infiltration would be my first step.

with any install you will have ductwork. if someone is suggesting
building soffits/furdowns to encase ductwork inside of the living
space..(if I read that correctly) this is an added expense that is worth it.
please clarify before I explain something that doesn't apply.

I'd prefer one unit and keeping all of the house conditioned all of the time.
otherwise when one unit is off humidity in house builds up & puts extra
burden on the unit that is on. then when the second unit is turned on, it
has to work harder to remove humidity & then cool off the area.

let me take a minute to explain about Relative Humidity inside the house.
when Rh is high inside the house (above 50%) it is a clammy feeling,
even turning down tstat (in summer) results in cool air but clammy feeling
persists. lowering Rh results in higher temp @ tstat, with air that is cold
& dry. when unit is off, Rh increases inside the house, it accumulates in
sofas, beds, walls, rugs etc. when unit is turned on..it first has to pull
moisture (Rh) out of these areas..and then cool. it can take 24+ hours
of constant a/c to do this.

in hot humid climates Rh is a big deal. control it and you'll be comfortable,
let it increase...you'll never be comfortable.

our main issue is dehumidification.
too much a/c and the unit doesn't run long enough to dehumidify.
this is called short cycling.
unit runs 10 minutes cuts off for 10 minutes..runs again..all day.
this costs you more to operate as start up of unit causes more electricity to be
drawn than unit running for a long time.
it shortens the life of the system, as warranties are based on estimated amount of
start ups for the life of the system.

with two units you are paying for twice the equipment, more ductwork,
more electrical upfront. then you'll pay to operate & maintain two units
from here on out.

two units will be oversized, hvac company won't put in 2) ton & a half systems
but 2) two ton..or three ton & two ton. then you'll be out of pocket, have high
operating costs & be stuck.
too many companies use what is called rule of thumb sizing for hvac systems.
different "methods" to determine from standing across the street & holding
up fingers to cover house & using one ton per finger..to 400-500 sq ft per ton.
these are simply wags. no methodology, just a guess.

instead you want to determine what the needs of the house are to cool it.
composition of walls, insulation in attic, external shade, etc all factor in.
load calculations (load calc, manual J) are used to size the system, using
all the unique to your house inputs.

without improvements in air sealing...you'll need a lot of a/c, but will
never lower Rh. so simple things like covering jalosie windows are good
things to do. a blower door test of the house will measure infiltration &
show you where the leakage sites are. this a good thing to do so that
you aren't trying to cool the great outdoors.
many utility companies offer 'free' audits. not the greatest...but it would
give you an idea of where the leaks are.
first air seal, then hvac system...then insulation..if ductwork is in attic.
air sealing is always first.

about hvac systems. like Fla. La. (usually) doesn't have much of a heating
season...this year being an exception rather than norm. so a heat pump
would be my recommendation.
heat pumps cool & heat. the outside condensing unit is a/c in summer,
and primary heat in winter. you still have an air handler unit (ahu) inside
with electric strip heat for when temps get to 30 degrees or lower & stay
there for a while.
otherwise the condensing unit provides the heat.
this is very cost effective, electric strip alone is the most expensive way
to heat a house. so why go there. the added cost for heat pump over straight
a/c with elec strip is worthwhile.

then you want to handle Rh. there are several ways to do this.
two stage condensing unit, variable speed ahu, dehumidifier.
each is an extra cost.

two stage a/c will operate in low speed most of the time, but when
more cooling is needed, the capacity is there. low speed is cost effective.

vs ahu less expensive option than two stage condenser but basically the
same low/higher speed control for when it is needed. (this is what I have)
with my vs ahu my indoor Rh stays around 55%.

dehumidifier. there are whole house dehumidiferes Ultra aire for example that
tie into ductwork/return air to remove humidity for the whole house.
with my 90 pint dehumidifier I can easily lower Rh to 50% & lower.
this is really great for 'shoulder seasons' spring/fall when little a/c or
heat is needed.
there are also stand alone dehumidifiers, like you purchase at lowes or hd.
but you have to empty them out, unless you can locate them centrally
in the house & tie into a drain.

you don't mention gas, so I didn't get into a/c gas furnace options.

its a common game for contractors to contradict each other.
getting bids that compare to each other is a pita.

ask for heat pump bids, with detailed info on duct/return proposals.
I like a good (13 SEER) better (15-17 SEER) and best (17+SEER) bid.
13SEER is the least efficient produced, 15-17 SEER is mid range but provides
a good system with humidity removal for optimal cost...and 17+ is good system
with humidity removal & bells/whistles.

get at least 3 bids with good better & best equipment.
then compare apples to apples.

I would stay with one system, in the 15-17 SEER range, invest in
ducts in furdowns (if that was the option) & R-8 reflective flex duct
that is properly strapped, and mastic sealed. (I'm assuming that flex
is what is being offered...correct me if I'm wrong)
no grey flex or black flex. reflective to reflect heat out of duct.

please clarify where ducts will be located.
inside furdowns/soffits inside living space?
in attic?
in crawlspace?

post a simple layout of your house...to see if furdowns
would even be an option.
include info as to where ahu/heat sys would be located.
inside living space (note on layout) or attic/crawlspace.

don't be fooled by 'brands'. each large brand has lesser known line also like
trane/american standard. if you get hung up on name brand...check with another
contractor that sells 'sister' brand, same equipment..different label.

install trumps brand.

these are the things that come to mind for me.
take your time...while it isn't too hot...& get your bids
lined up. try to plan install before heat of summer gets here.
sometimes when things are slow..you not only get a better install
but a better price.


best of luck.

 

[energy_rater_La]

it took a while! I'm sure there is stuff I missed, just trying to give OP the
headlines...y'all can fill in what I missed (and there is lots!)

 

[energy_rater_La]

looks like OP has forgotten that they posted here.
oh well...that's time lost forever.

fwiw...window change out would be something I would
recommend for jalosie windows. and I don't often recommend
changing out windows, as there is a small energy savings
(about15% in my hot humid climate) and a 30 year payback
on average ( small house 10 windows ) higher payback for
bigger house/more windows.

in this case it is the leakage of the jalosie windows that is
difficult to address. glass doesn't seal well to glass.
hands down jalosie windows are the leakiest windows I've
ever tested...with the exception of double hungs with missing
window panes.

air sealing would be first order, thus the not attractive option
of shrink wrapping windows.
of course...who knows what the walls are built out of...
oh yeah the OP knows! LOL!

 

[energy_rater_La]

of course mini split bid was highest. no ductwork to install, no holes to cut for supply boxes etc.

while replacing windows would be a down the road option, installing double hung or casement
windows would still give you egress. my understanding is that this applies for bedrooms,
one egress point being the door into the room, the other a window to exit from if
door is not an option. call your local code office to clear this up...for future plans.

shrink wrapping windows would be your least expensive option.
I don't know of any local to you companies who do this, you would do better
to investigate that. usually this is a diy project, razor knife, blow dryer..it isn't
rocket science. do a google search & it will show products, and even some
videos that make it look easier than it is. cheap materials, so if you ruin one..
it is no big loss..just the learning curve.

you haven't given any info as to what type of system...a/c elec strip, a/c gas heat
or heat pump that you are interested in, or what was bid...or any indication of understanding
different types. that is input that is needed if we are to assist you in your educaton/decisions.

so attic has limited space due to cathedral portion of house.one option would be
to install open cell foam on the roofline of the portion of the attic that allows it.
for the cathedral area, foam would go on walls of these rooms (attic side of course)
to eliminate heat gain through the walls.

your best option for ductwork would be to fur down the hallway, and build furdowns
(or soffits as I believe you call them) to serve the other more open part of the house.
this can be done attractively, with a little planning.
heating system ahu would go in closet, return would be @ bottom of closet.
supply plenum above coil, ducts for bedrooms
in hall furdown, ducts for other part of house in individual furdowns.
then you simply paint furdowns to blend in, or stand out whichever
you perfer.
not all houses can easily be furred down, you are lucky in that respect.

did you gain any insight from my earlier posting of types of central
systems? any questions on that?
I know you said masonry construcion, which can mean several things.
concrete block? on exterior & interior? concrete with sheetrock walls to interior?
insulation? something different? there really is a reason for all the questions.

best of luck.

 

[energy_rater_La]

pricing not allowed.
I understand about the minimal need for heat, but the few winters
that you need heat..elec strip operates at a premium price.
knowing your utility costs per kwH would be helpful.

needing dehumidification, I'd upgrade from minimum 13 SEER to
that midrange..15-17 SEER
if electric strip for heat, then two stage a/c
if heat pump (still my recommendation) then variable speed air handler unit.

see my first post on the differences.

efficiency costs are always upfront, but benefits for life of system.

you could check with energy raters in your area through resnet, a phone consult
might would help to clarify what is most affordably efficient in your area to you.

oversizing will be the problem, short run times, higher costs to operate, little
humidity removal. thus the questions about walls??? as you have explained
attic/window situation...walls are the missing piece of the puzzle for us.

designerdan should be along with is florida info...

 

[energy_rater_La]

yes avigaylis, that was the wall info I was looking for.
I agree that wall insulation is at highest R-4, but likely lower.

glad to see Dan posting, as this is more his area/construction of homes
than mine. while heat pumps may not be for your area, it was my best guess
in explaining operation of different systems. not knowing which parts of the
state that heat pumps are the best choice is on me, I do know other
energy raters in Fla that have heat pump...but couldn't say which part
of the state they reside in.

as for your friend with same size house/windows etc, she/you could probably put
5 tons of more & still have cooling issues.
the windows themselves contribute greatly to humidity inside the house via air
leakage.

rather than throwing $$ at more tons of a/c, addressing the window leakage issues
and other improvements to the house itself would be the better investment.
solve leakage/RH concerns & smaller unit will dehumidify so that house is both
cool & dry.

in your picture, is there any vapor barrier at block wall or lathes of walls?
could you post the pic?

concrete block houses alway stump me, I lived in one for a few years &
in the winter we had to move the furnishings away from exterior walls because
of condensation on inside of walls. it was so bad it caused mildew to grow on
everything. (sure was glad to move from there!)
concrete block homes in my area usually have foam sheathing on interior of block,
2x4 framing, insulation & then sheetrock. mostly though block is for commercial.
just an example of how things differ in different areas.

 

[energy_rater_La]

I am impressed with your interest to get an understanding of all of this.
X2

 

[energy_rater_La]

amazing, I guess since the temps there are so mild that uninsulated
walls aren't an issue?? seems that walls would need vapor barrier somewhere...