On Jun 4, 12:25 pm, wrote:
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.)

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