I'm trying to replace the built-in mechanical thermostat on an old
Fasco Industries 8- foot, 240 volt electric baseboard heater with a
programmable line voltage thermostat, either a Honeywell CT1950 or an
Aube Technologies TH106. Problem is I'm supposed to choose between 2
programmable thermostats - the Honeywell CT1950A which is for 2 wires
or the Honeywell CT1950B which is for 4 wires, and I have no idea
which one I need.

Questions:

1. Is the CT1950A or B just one thermostat that can be wired in 2
different ways, or are we talking 2 different thermostats altogether?

2. In any case, how can I tell if I need a 2-wire thermostat or a
4-wire thermostat? I looked at the existing wiring and noticed that
there are only 2 wires coming out of the wall directly from the
breaker panel. Then there appears to be 4 wires, all of them colored
red, connected to the built-in thermostat mounted on the heater itself
- 2 red wires going in and 2 red wires coming out. I have not traced
where these wires going in and out of the existing thermostat are
coming from.

As you can tell, I am really electrically challenged, so please pardon
me if the question sounds stupid. But I really have a problem
understanding electrician's English - when they say 2-wire or 4-wire,
are they talking about the wires coming out of the wall or the wires
coming out of the thermostat?

Any help will again be appreciated. Thanks.