"John Hines" wrote in message
news
"CBHVAC" same @as.it.was.com wrote:
"Howie" wrote in message
...
I am shopping around for a central air conditioner that will be
installed
in
our 850 sq. ft home... any advice?
Howie
Google. This gets asked 200 times a month it seems.
Bottom line, make it easy for you:
The installer, not the brand, makes the difference.
Do not let anyone install the unit that does not perform a manual J, and
D
or T (heat pump calc) on your home to insure it is sized correctly, as
there
ARE NO RULES OF THUMB in this trade.
Where can I, as a home owner, find out more about this manual J & D
thingy, and the info required?
Manual J, is a standard heat loss/gain program. It allows the contractor,
after measuring each room of your home, figuring the total construction
values, type of window, glass, doors, number of doors, sliders fireplaces,
ETC, basically the entire structure, to know exactly how many BTUs will need
to be given, or taken from each and every room that is in the home to
maintain a set temp, regardless of the outdoor temp, to a point.
Manual T, is the same, only it is for heat pumps.
Manual D is the calculation that takes into consideration the type of duct
system that the contractor will install, the material it is made of, and the
total effective length of each run, that will properly size each and every
duct that feeds from the unit to each room, that will allow the unit to
maintain its optimal static pressure, and each duct will have the proper
volume, and velocity to deliver the needed BTUs, or to remove the needed
BTUs from each room. It takes into consideration the unit, the coil, wet and
dry, each and every bend, the registers, the type of filter and filter
grille, grille face velocitys and such.
You might find info on the net, but to be perfectly honest with you, I tend
to trust the manuals that I am required to have...it takes a bit longer to
do them on paper, and I do at times use a program on the laptops to verify
that I didnt make a mistake somewhere since its not a walk in the park, but
I just dont really 100% trust the computer programs...nor alot of the info
you may or may not find on the net...I trust what ACCA states...thats it.
I'm wondering what info is required, since I've got a bunch of
electronic equipment that heats things up, which of course, needs to be
factored in.
In a nutshell roughly:
Each rooms dimensions, including ceiling, and ceiling height.
Drywall thickness,
Insulation values, and failing that, type and thickness
Window sizes, and type of glass, single, double, triple pane etc, and if its
a Low E construction.
Wall type
Frame, or mason construction
Number and size of every door to the outside, including sliders
Direction the home faces, N, S, E or W.
Direction each door and window faces,
Total running wall
Area below grade, (basement) or if the home is partially built below grade
Slab, or non slab construction
Roof construction, and color
Any shade, natural, or manmade..
# of fireplaces, (air infiltration)
CFM of outside air that may be brought in, such as from a bathroom fan, or
dryer, or kitchen vent fan.
# of people that will live in the home, + 1 or 2 additional if you entertain
or have family or friends over often. (each person adds 300 BTU, or more)
In the event of a computer room, number of units total, and types...
Location geographically of the home
Number of Degree Days for your area
Percentage of RH...normally now figured at 55%, can be figured as 50% in
residential, but 55 is the accepted standard now.
You take all that and some more, run the numbers, and depending on the
actual design, construction, and location of the home, your tonnage may vary
greatly.
We recently did a fairly large home, on slab, that had R80 ceilings, and R60
walls, and when it all got figured, the number of BTUs were very small
cmpared to a standard home. Matter of fact, it worried me so bad that I ran
the numbers 4 X to make 100% sure I had not made a mistake at some
point...and sure enough, 2 years later, the homeowners cant be happier.
Theres actually more, but its all factored in as you go.
Currently, I'm working on venting, and making sure there is air outlets
and returns in the rooms, but a new main unit is planned.
You cant do the returns and supplies, till the load calculation is complete.
If you are using gas as a heating source, the gas line has its own
calculation that must be done.
ANYONE that is going over the plans, and starts quoting prices and tonnages
needs to be dropped....period.
Some will charge for the calculations..make sure that if they get the job,
that is no longer a charge, and given back to you in some form, be it a
rebate of sorts from teh contractor.