"HVAC" wrote in message
...
On 12/14/2010 3:53 AM, ftwhd wrote:


FWIW, I have *NEVER* seen a furnace gas valve with a
"variable dial" on it.

Here ya go:

They make em steve. They have a sensor that goes in the supply air
and you set the valve according to the supply temp that you want.
Usually see them on direct fired make up air units. Seen them on
Reznor gas fired duct heaters too.


Ya. Much as I hate to agree with ftwhd, I worked
on a Marv-Air make up air unit yesterday that had
a variable gas valve.

The only "variable" adjustment I have seen is the manifold pressure
adjustment.... but then I don't do commercial or industrial stuff as a rule.