On Thu, 20 Nov 2003, CBHvac wrote:

"Steve Stone" wrote in message
...
Don't most stats have a plus or minus 3 degrees or so in latitude in when
they turn off or on ?

They do.
There is a reason for this, and a good Honeywell mercury switch stat, can be
better than a Chronotherm model when it comes to comfort.
Its called a dead band, and since MOST people can not actually feel the 3F
difference in temps, you never know.

The RobertShaw thermostat that came with my house was +-1 (2 degree F
spread) at best, and usually overshot 1-2. It had no anticipator setting,
just gas/electric switch.

I changed to Honeywell CT3500 (should have gotten CT3600) with 1 degree
spread, and by comparing air and wall termperature learns to
electronically anticipate temperature rise to shut off before it reaches
setting if necessary (since steam radiators retain heat), and ramps up
from setback instead of all at once. It only rarely overshoots slightly
if the weather suddenly turns very mild. The only reason I would have
liked the CT3600 is because it logs total run time to tell most effective
setback.

I don't know if the original poster gave a model number or whether it was
wired or set properly for their hydronic system. But my Honeywell
electronic works great for single-pipe steam, although, I my old home has
plenty of thermal mass (drywall over plaster), so temperature changes are
never sudden.

--
David Efflandt - All spam ignored http://www.de-srv.com/
http://www.autox.chicago.il.us/ http://www.berniesfloral.net/