Art Todesco wrote:

I will be setting up a small fan to equalize temperature in 2 different
places. This is actually in a church to keep the temperature of the organ
chamber, close to the temperature of the church itself. The reason is to
keep organ pipes in the 2 locations, in tune with each other.

With a common air supply from the wind chest, all the pipes would tend
to have the same temperature after the organ is played for a while. If
you can make air flow a lot of pipes at the same time, the backpressure
and fan pressure could be low, but maybe that's hard to do, if springs
in the chest hold valves closed until solenoids open them.

... I was wondering if anyone knows of a simple unit that is capable
of switching 110 to the fan. The fan will be a small, 300 CFM or so
unit, using just a few amps.

Running the blower before the organ is used, or whenever the church is
occupied (with an occupancy sensor) might use less energy. Heliotrope
General makes a 120 V differential thermostat, but the min differential
is fairly large, about 5 F.

With a dT (F) temp diff, 300 cfm would move about 300dT Btu/h of heat into
the pipes, which might lose heat from their surface at 1.5 Btu/h-F-ft^2
to church air at different temperatures. If one part of the church is
50 F and another is 70 and each contains pipes with 300 ft^2 of surface
and each receives 150 cfm of air at say, 70 F, the warmer pipes will be
70 F and the cooler pipes will warm to 55, for a 15 F temp diff. With 60 F
supply air, the warmer pipes would become 67.5 and the cooler ones would
become 52.5, with a 15 F temp diff that would decrease with more airflow but
doesn't depend on the supply air temp. Like this, viewed in a fixed font:

Tc = 50+1125/450 = 52.5
|
1/150 | 1/(1.5x300)
60 ---------www-----------------www--------50 F
|
| I = (60-50)/(1/150+1/450) = 1125 Btu/h --
|
| Th = 70-1125/450 = 67.5
| |
| 1/150 | 1/(1.5x300)
----www-----------------www--------70 F

--- 1125 Btu/h

A clever controller might measure the pipe temps and route 300 cfm of 70 F
air to the cooler pipes, raising their temp to 58 while leaving the 70 F
pipes unchanged. The chest might also contain a 1500 W space heater.

A small house furnace blower might work. Large organs have blower motors
rated in horsepower. You can't open the door to escape from the chest in
the First Parish UU Church in Concord MA until you turn off the blower or
open a small door slider to lower the air pressure from about 5" of water,
which pushes the 2'x5' door closed with about 300 pounds of force.

Nick