This is an ordinary three bedroom home with:
An ordinary central heating and air conditioning system.
Central system has ordinary sheet metal ducts, in the attic, to each room. 
Each room has adjustable inexpensive sheet metal louver vents.
One thermostat in the hall controls the temperature for the entire home.

There is one hobby room, that needs a lower temperature then all of
the other rooms.
The adjustable louver vent in the hobby room, is not adequate to
control the temperature.

My question is:
Can I change out the inexpensive sheet metal louver vent, for a new
quality 1 room ?electric louver vent?, that has its own one room
thermostat, to control the electric louvers.

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Request for Question Clarification by maniac-ga on 02 Jan 2005 18:13 PST

Hello Clicker5,

What you describe does not seem to be a complete solution. Let me
rephrase your question slightly and see if it clarifies the situation.

[1] hobby room, needs a lower temperature than all other rooms

[2] central heating [and air conditioning]

[3] replace fixed vent (in the hobby room) with an adjustable one that
has a separate temperature control [to reduce the heating effect] to
control the adjustments

If all of these are correct, what you describe should work when
heating the home, but fail to work when cooling the home. The best you
would get in the hobby room when cooling would be roughly equal to
that of the rest of the home. If you need a solution that works for
both heating and cooling, you may need to add equipment (beyond the
electric louver) to the hobby room. Please let us know if that kind of
solution will satisfactorily answer your question. If I have
misunderstood the situation, please clarify your question.

Thanks.

  --Maniac

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Clarification of Question by clicker5-ga on 02 Jan 2005 21:29 PST

Hi maniac-ga
Let?s just take the heating problem.
When it is cold outside, and the heat is on, the hobby room is the
hottest room in the home.
The hobby room has one window, and is the best insulated room in the home.

If the hobby room had its own automatic thermostatic vent closer, and
the thermostat was set lower then the hall thermostat, the hobby room
could be kept automatically cooler then the other rooms in the home. 
Of course, in this event, the hobby room door to the hall would be
closed.

There is no need to discuss the air conditioning.

My question is simple:
Is there a quality device available, that will automatically open and
close a room vent?
Regards,  clicker5-ga

Hello Clicker5,

Thank you for the clarification and the short answer is "yes".

The general term for what you are trying to do is to set up more than
one "zone" of heating / cooling. For example see
  http://www.acdirect.com/matrixd3.php
for an illustration of the concept (the picture shows three zones) and
an explanation of a couple of the items (zone damper, bypass damper)
included in the controls. This vendor has several solutions from two
to seven zones.

From what you describe, a two zone system should be adequate but a
bypass damper may be required. This solution would work for both the
heating and cooling of the room. During cooling, the bypass damper
would be used when the A/C is cooling the relatively small hobby room
to prevent overpressure on the blower and ducts.

Honeywell has a nice explanation of how to choose and place components starting at
  http://content.honeywell.com/yourhome/zoning/zoning_home.htm
or more specifically at
  http://content.honeywell.com/yourhome/zoning/zoning_manual/zoning_sec_1.htm
  http://content.honeywell.com/yourhome/zoning/zoning_manual/zoning_sec_2.htm
  http://content.honeywell.com/yourhome/zoning/zoning_manual/zoning_sec_3.htm
  http://content.honeywell.com/yourhome/zoning/zoning_manual/zoning_sec_4.htm
  http://content.honeywell.com/yourhome/zoning/zoning_manual/zoning_sec_5.htm
For example, it recommends placing the dampers at least 3 feet away
from the plenum to reduce turbulence in the duct. I did not find costs
on the Honeywell site, but a local supplier should have that
information or see
  http://www.airmechanicalinc.com/zoning_system.html
for a listing of several Honeywell control products / pricing on the web.

For other vendors with similar options see:

  http://www.iaqsource.com/index.php?module=products&prod_cat=56
listing "Jackson Systems" motorized dampers in a variety of sizes (to
fit into your current air ducts) and
  http://www.iaqsource.com/index.php?module=products&prod_cat=54
for the zone control units. This appears to be a good source of
products if you can do the design yourself.

  http://www.trane.com/Residential/SelectSystem/ZoningSystem.aspx
for system selection for residential zone equipment at Trane (they
basically recommend a professional to design / install the system).
This would obviously be more of a "complete solution" (design,
installation, set up).

  http://www.ewccontrols.com/ultrazone/ultrazone.htm
or
  http://www.ewccontrols.com/ultrazone/ultramap.html
(the latter page loads a lot faster and basically goes to the same information)
which has a good set of pages describing a range of products to build
up a zone system.

  http://www.resconsys.com/products/zonepanels/
another vendor of zone heating / cooling products.

I have tried to limit the answer to "residential" (and not commercial)
components to keep the costs down. I was somewhat surprised at the
costs of these components as I prepared the answer so I am providing a
couple alternatives at the end of the answer.

Search phrases included:
  heating vent control adjust automated temperature
  heating vent control adjust automatic temperature
  zone bypass damper
  residential zone heating cooling

Other options that may be more cost effective (than a full zone
control system) and may help solve your problem includes:

[1] Reduce air flow into the hobby room (by adjusting the vent or
adding an in line damper). If the room is now "too cold", add a space
heater to make up for the difference. Lowes (http://www.lowes.com/)
for example had several space heaters described as "zone heating".  It
may be feasible to adjust the vent twice a year (once for heating in
the fall / once for cooling in the spring) to get the most benefit
from this approach.

[2] From your statement (about the window), I assume the hobby room
window has a south or west exposure. Another alternative is to add a
reflective coating (or darkened glass) to reduce the heat coming into
the room from sunlight. Of course, draperies could also be used but I
assume you want some light from the window.

If some part of the answer is unclear or does not fully meet your
needs, please make a request for clarification so I can correct it.

  --Maniac

Hello maniac-ga:
Thank you for the answer.
clicker5-ga