"Manual J" A/C tonnage calculation
bubba...@yahoo.com
residential detached home?
(Case in point: a 1966 brick ranch home in Denver Metro; 1400 sq ft
main level, 1200 sq ft basement.)
What is the procedure to follow? Download the Manual J spec and follow
the instructions? Or is there some kind of software or Excel
spreadsheet that will make the calc easier?
I know I'm supposed to insist that the HVAC contractor use the Manual
J method, but how do I verify that that they indeed did it correctly,
took all the factors into account, did not cut corners in the
formulas, etc?
cheers
dpb
> How hard is it to do the "Manual J" A/C tonnage calculation for a
> residential detached home?
Not particularly hard, does take some experience/expertise to get good
data estimates as input...
...
> I know I'm supposed to insist that the HVAC contractor use the Manual
> J method, but how do I verify that that they indeed did it correctly,
> took all the factors into account, did not cut corners in the
> formulas, etc?
That's why you look for a competent installer...if they're good,
they'll show you and go over the sizing calculations w/ you. If
they're the typical, they'll send out a "hired gun" commisioned sales
rep and he'll wave his hands and guesstimate, most likely looking at
the existing system and copying it.
Of course, if you have had an existing system and it performed well
before dying of old age, that's not too bad. OTOH, if it's a first-
time installation or other factors have changed markedly, it surely
deserves a fresh evaluation. (It deserves it anyway, but is far more
likely to be adequate if have had previous success, obviously.)
--
DT
bubba...@yahoo.com says...
>
>How hard is it to do the "Manual J" A/C tonnage calculation for a
>residential detached home?
>
>(Case in point: a 1966 brick ranch home in Denver Metro; 1400 sq ft
>main level, 1200 sq ft basement.)
>
>What is the procedure to follow? Download the Manual J spec and follow
>the instructions? Or is there some kind of software or Excel
>spreadsheet that will make the calc easier?
I don't think there is a source for free Manual J software. I had to submit one
for the addition I built to my home. I used Hvac-Calc, here is a link. It's $49
for a one time license. It works quite well, you enter every wall, ceiling,
floor, window, door, etc into the program. The results show heat loss/gain for
every room, plus totals. It passed my building department just fine.
http://www.hvac-calc.com/main.asp
--
Dennis
v
>How hard is it to do the "Manual J" A/C tonnage calculation for a
>residential detached home?
>
It aint rocket science.
Get a look at the procedure, and then set up your own spreadsheet if
you don't want to pay for one already set up.
My first job, back before PC spreadsheets, was doing these types of
calcs. At least I had a 4 function calculator. I started with a
slide rule.
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