On Mar 28, 7:52*pm, bud-- wrote:
Tony Hwang wrote:
wrote:
On Sun, 28 Mar 2010 17:09:05 -0600, Tony
wrote:

Hi,
When I was replacing blower motor on our furnace
there were two replacement choices 1.0 Hp or 3/4 Hp 3 speed
motor. Between two only difference was Hp rating and full load
current draw. As an after thought I wonder if there'd be any advantage
choosing the 1.0 Hp one. BTW, our a/c unit is 3.5ton.
TIA for any experienced comments.

You really should be consulting the installation documentation of your
system. That is not as simple as just saying bigger is better.
The air handler and the condenser have to be matched.
Hmmm,
Not knowing anything HVAC. I put in 3/4 Hp one as the manual states.
But curious duck wannna learn. Any pointers where to look? Getting
old guy has to exercise his brain, LOL!

As everyone said, replace with what the manufacturer says. It is an
engineered system.

You could run a larger HP motor at a higher RPM (which as others have
said is not necessarily a good idea). Running at a higher RPM requires
changing pulley size if belt driven. Not easy for direct drive.

The motor might run very slightly faster because it is not loaded as
near to its rated HP. That would slightly raise the current and
electrical power used. It should run cooler. I believe it runs more
inefficiently, with increased losses. I believe efficiency is the major
reason not to increase the HP. Starting current would be higher, which
existing equipment might not like. But it should be up to speed faster.- Hide quoted text -

- Show quoted text -

No heating air conditioning experience but could it be rather like
dropping a V8 motor into a six cylinder vehicle and then finding out
that the gear ratio is wrong and due to increased HP the next size
universals and/or rear end ratio should be changed!
There must presumably be a proper balance between speeds, the load of
air to be moved etc. and arbitrarily changing one factor might need
some other adjustments? Could also be like trying to use a large pair
of kitchen shears to cut ones fingernails; or a using a chainsaw to
try and cut plywood panelling?
Reminds one of friend who, years ago, put in a 'waaay too large' an
oil fired air heating furnace. He got it at a bargain! It ran so
infrequently, even in very cold weather, that it was highly
inefficient; finally replacing it many years later, with electric
heating.