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 sn 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.
As everyone said, replace with what the manufacturer says. It is an
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.
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
It's similar, but you're not changing the gear ratios. You have a
larger "motor", but are not asking it to deliver more power. The
speed of an AC (induction) motor is more or less determined by the
line frequency. A motor with a higher HP rating will turn the same
blower at the same speed (give or take a little).
Talking about jumping from the frying pan into the fire!
The HP depends on the size of the fan blades/cfm the blower has to move. If
the HP is too much it will only draw more current and cost more to run if
the relay and wiring will handle the larger current.
If the HP is too small for the blower fan, it will overload the motor, it
will slow down and burn out and not move enough air. This could also lead
to a burnt out firebox if gas or oil and poor cooling for the
So long as the motor is not exceeding it's rated current (Amps)
depicted on the nameplate, there is no need to worry. There is no
point in putting in an oversized motor. So, if you're worried, you
need to borrow a meter that can read amps & check it out. But if it
was 3/4 HP before, it's gonna be 3/4HP again.
Original motor spec. is 3/4, 2/1, 1/3 Hp, 3 speed of which first two
speed are used high speed for cooling and medium for heating.
The 1.0 Hp motor had 1.0, 3/4, 1/2, 1/3 Hp 4 speed. My thought was
with this motor I could have more options. Also this motor had ball
bearings vs sleeve bearings. I understand ball baerings last longer.
Any how furnace is back up and running again. Next is time to replace it
when breaks again. Price difference was like ~40.00
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