There are a few that use solid-state components to activate the HVAC
equipment, and these may be described as having battery backup, but running
on the voltage provided by the HVAC equipment. But most of the units are
more universal in their design, so they work on the majority of control
systems used on HVAC equipment.

Unfortunately, the best and most universal way to activate the HVAC
equipment is with dry contacts, the kind that small relays have. Being an
electro-mechanical device, when the contacts activate, there is some noise
associated with that action. Some are noisier than others. The relays are
small, the contacts are small, so to make a good connection they must really
"snap" into position.

After a while, either you get used to it, or you move the thermostat around
the corner to a room or space where you can't hear it anymore, and hope that
the resulting temperature is still within your comfort zone.

The original Honeywell round thermostats use a mercury switch inside that's
totally silent as it makes the connection, but this kind of unit is not
digital and can't be programmed. I would not be surprised however to find
that the Honeywell units are very quiet, if not silent, so it may be worth
buying one and trying it out. If there's no improvement, or it's too noisy,
you should be able to return it to the store where you purchased it.

Bob M.
======
"Dave Gallant" wrote in message
om...
Greetings:

I have a Hunter Digital Thermostat [Set and Save 110], and the relay
makes a "click" noise every time the unit calls for heat. Their help
department tells me that this is a normal function of this unit.

Is this a standard operation of all digital thermostats? If not, I
will be making a change. I have an office setup within 15 feet of the
unit, and the sound can distracting. Suggestions on a good replacement
would be appreciated - heat only, for hot water baseboards.

Thanks,

Dave