Because you'd want to be sure that the system was sized correctly.
Maybe your neighbors with identical homes are all oversized, too. That
would be quite common. The ONLY way to know is to do a heat gain
Or live with the question. Your choice.
Hmm. Young first time buyers may not know there's something better than what
they already have. That happens with many details of home ownership, as well
as car maintenance, boat maintenance, garden maintenance.
Engineering isn't science? I'm never driving over a bridge again! And by the
way - it's possible to install an AC unit that's too large for your house.
It'll cool the air down quickly, but not run long enough to remove humidity.
Bummer. Makes for a clammy feeling house.
Hes not a mechanical engineer?
So, basically, you are having an electrician, do your mechanical
work....thats like hiring a plumber to do sheetrock.
As someone that IS in the field of mechanical work, yes, all three can make
the same mistake, and all three can talk to you like you want to be talked
If no one did a proper manual J, or T, or D, then all 3 are screwing you.
You want professional work you should expect professional work.
If no ones done their work, then its all guesstimates.
Any legitimate contractor, will: Document every move on a job. Document
every sizing calculation to defend his position, and in most areas now, any
AC permit must have a load calculation with it, so that in the event there
is a mold claim at a later date, the contractor can show where he sized the
unit properly, and installed it correctly to code.
He will also document any changes to the original agreement with a change
order, signed by himself, the homeowner and any subs involved.
While respect, reputation and trust all factor in, you dont get that way by
not doing your job properly.
I can also tell you that depending on your region, a 15SEER unit wont be the
same size as a 10SEER on the same home.
You also can NOT use the same duct that a unit installed in 1971 used on a
new 12SEER unit, much less a 15SEER.
If you are truly an engineer, you understand why proper calculations are
important for you to have the correct information on paper when all is said
and done....therefore, going on a mans word, isnt the way you want it done.
Also, have you asked your friend how many calculations he will do AFTER the
unit is installed to insure you have the SEER you paid for? You should get a
sheet with over 100 calculations done, AFTER the unit is installed, showing
that you have the proper SEER. Meaning, in plain English, you paid for a
15SEER unit, are you really getting 15SEER, or only 10?
As a homeowner, anyone I hire to work on my home better back up their talk
with some facts. Being in a building trade, as a company owner, we get to
see alot more than the average man, in regards to home repair, and
contruction. We see some real crappy work, and we see some real nice stuff
that would be called overkill by some. One thing we have learned is that the
low bid is not always the wrong bid, nor is the high or middle bid always
the best....however, we have been, and continue to be staunch in our
position that most HVAC contractors are rapists, not all, but most, and
since the average man knows little to nothing about the trade, these guys go
out, and rip people off daily. They are not the ones you find posting in
self help groups, or in the alt.hvac group. They are the ones that charge
$300 to show up on a Sat afternoon, and do nothing. They are the ones that
charge $35 a pound for refrigerant and never use a scale....they are the
ones that think that charging a system only requires the use of a jug of R22
and a set of guages...nevermind the other 5 to 10 tools that are required to
do it right.
If you are NOT getting documentation to the size of the unit, HOW that size
was come to, the duct layout, WHY that duct layout was needed, and
documentation about the final testing, you are getting screwed. Period. You
can be happy with the price you paid, you can be happy with the
installation, you can be happy with it all without it, but bottom line,
without it, you have a POS installation, since all the legwork was not done
I'm going to buck the experts here. Forget the Manual J.
In a new house, new design, I'd agree 100% that the Manual J calculations
should be done. If, however, you'll lived in the house for 15 years, it has
been very comfortable with a given sized unit, it is the same as 10,000
other similar homes in the region that have the same sized units and are
comfortable, I'd trust the guy with 35 years experience to say, "yep, this
size is OK".
I don't care how well the calculations are done, the situation will change
anyway. You have three more kids that add body heat and more laundry and
the associated heat load. Cooking heat load. A big tree gets cut down. A
small tree grows up. The four teenagers you have now move out of the house
and it is just the two of you. You add a better storm door. You leave the
garage door open. All these things affect how well the AC works in YOUR
I told the story before. I used to quote tooling for our company. I'd do
the estimate in less than five minutes. The engineer in the machine shop
would do the calculations over a period of three days and a few hours of
actual calculating and getting quotes from suppliers. We'd be within $100
or less on a $10,000 tool, every time. He felt the need to do the math each
and every time. I started out looking at what he quoted for a similar item
and use his numbers over and over again.
If you feel comfortable with the guy, he is probably the best for you in
Panning joists violates the codes in most areas. Not doing a load
calculation also violates the codes. What other code mis he going to
violate. He may explain things, but he must be explaining things wrong
if violating codes is ok with him. Check the International Mechanical
Code and International Residential Building Code, now used all over the
USA, except in the few places where there are no codes.
Dear Sir or Maam
You really need to watch your vocabulary. The words "Heat Fuct" is
not a nice thing to say on a public newsgroup. If you dont like your
heat, simply state that. There is no need to use the "F-word" or any
derivitive of it. And just for the record, heat is not capable of
fornicating, just like neither is a hammer (to those of you who say
something like "hand me that fu__ing hammer). Inanimate objects are
not capable of fornicating. To reproduce, they need workers and
factories, and none of these objects are ever given a birth
certificate because they do not actually reproduce, they are instead
manufactured in mass quantities.
Please go wash your mouth out with soap now !!!!
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