Michael Gallagher wrote:

On Sun, 15 Jan 2006 00:57:16 -0600, RP
wrote:



It will shut off when the demand is low enough ....


Just so I'm clear on this, "demand is low enough" means "the temp gets
to the setting on the thermostat," right?

The t-stat doesn't operate the boiler. The boiler will maintain an a
preset outlet water temp to the best of its abilities via an adjustable
internal temperature control. The internal control modulates the gas
valve in response to changes in water temp. The colder the water gets
the more the valve opens. The valve will thus raise or lower the burners
in response to the demand put on the unit. This is, believe it or not,
much more efficient than simply cycling the valve on and off with a
conventional thermostatic on/off control.


Sorry for seeming to somewhat anal, but this thought came to mind: The
Ultra's fuel efficency wouldn't do me much good if it runs 24/7!

It won't run constantly all the time, only when there is a high demand
put on it, but still no worries. Depending upon water temperature
setpoint, the burner may or may not cycle completely off between calls
for heat at the t-stat. There are several factors involved, including
whether or not the boiler is being used for central hot water in the
house, whether hot water is being used to take a shower, wash clothes or
dishes, etc during the heating system off cycle. The boiler system is
designed to modulate the flame height in lieu of cycling off. Excessive
cycling kills burner efficiency, as the air/fuel mixture and stack flow
attempt to stabilize. In addition at low fire more of the heat generated
gets transferred to the water. Modulating the flame to a lower level
prevents cycling for the very purpose of *increasing* efficiency. Though
it may run longer at low fire, it is using less gas while it is running.
The end result is a net fuel savings.

hvacrmedic


Mike



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