In article ,
says...

What Martin said. Get the ssr output board. A mechanical relay has a
life rated in number of contact closures, maybe a couple hundred
thousand. With the controller in time proportional mode, with a time
interval of 2 seconds (for instance), a mechanical relay would hit
200,000 cycles in 4.6 days.

That sounds like electrical life at full load. Mechanical
life at low current, which would be the case driving an
SSR, is typically in the tens of millions of cycles. For
example, IDEC RH series cube relays are rated for 50
million mechanical cycles. That'd be about 14000 hours with
a 2 sec cycle.

I also put a mechanical relay in front of the power side of the
control relay and control it with another high temp alarm controller
with separate temperature measuring device, or failing that, an alarm
relay (sometimes already there, sometimes an option) in the main
temperature controller. The separate high temp controller is required
where I work. It can be a much cheaper simple on-off controller.

Definitely a good idea. I'm furnace-less right now because
the cheesy controller on my little Thermolyne furnace
failed and burned out the elements.

To the OP - If you end up scrounging a controller that has
a relay output, I have a bunch of SSRs that have a self
powered input, so wouldn't require a controller with SSR
output or a separate power supply. The downside is that
they're only rated 15A @ 120VAC. But you're welcome to one
if you think it'll work for you.

Ned Simmons