On a new build, (the conversion of an old stable block into a habitable annexe), our electricians installed three electric oil filled heaters which are controlled by a thermostat, which operates a relay. The noise of the relay switching on and off is very loud, not much different to the nail gun they were using during the build !
The point is, the annexe will often be used for family sleeping over, and the relay noise would wake them repeatedly throughout the night as the radiators kick in periodically.
Are all relays this noisy? And do the rads need a relay to control them? The builder knew that it needed to be a quiet environment, so I have some grounds to demand a change, but I don't know if I have any options …. I've never seen relays employed like this an I'm not sure of their purpose.
Best Answer
No, not all relays are that noisy. Indeed, a solid state relay will make no noise whatsoever. For example, the Honeywell rt850t-240 is an example of a heater control relay that is silent. You can read about that here: http://bit.ly/1Caf1np
NOTE: I do not claim that this relay will work for your particular application. This is just an example. However, I believe you should be able to find something similar that will be completely silent.
To answer your other question, a relay is required because standard thermostats run on 24V, and the heaters are either 120 or 240 (actually, there are a number of other good reasons why you'd want to use a relay instead of having the thermostat switch the load directly, but that's the easiest to communicate). The Honeywell relay I linked to above connects to a standard 24V thermostat and will switch a relatively large 240V load.