On Jul 12, 12:03*pm, RickH wrote:
On Jul 10, 11:23*am, Lee B wrote:

Current house came with a whole house fan (not an attic fan, but the
kind in a hallway ceiling that sucks air into the attic). I was happy to
see that because I really liked the one in my old house. However the one
in the old house had a variable speed dial on it, and the new house's
fan has just one speed - high and loud with a simple off/on switch.

Is the variable speed a function of the fan itself or can that be added
at the switch? I'd definitely be having an electrician do it, but I'm
just trying to figure out if it's even doable, or if I'd end up needing
an entire new fan. And if so, would replacing an existing fan and switch
be difficult (ie cost me an arm and a leg)?

Whole house fans are great. *Yes you can put on a variable speed
controol, but I suggest you over-rate the control amperage you buy by
double. *For example if the fan draws 5 amps then get a 10 amp
control. *Also when turning it on make sure the control passes through
the higher speed, then you lower it. *This is so the motor gets enough
starting current. *I replaced the Off/High/Low switch on mine with a
variable speed. *You only use the High speed motor input wire, just
cap the low speed wire.

That depends on the motor. If it's a universal motor it'll probably
work fine. If it's an induction motor, probably not. Induction
motors tend to be "constant RPM" or with a given load, "constant
power" devices. As the voltage is reduced they'll want to maintain
RPM, which requires the same power, thus current increases.

If the fan is belt driven it's probably an induction motor.