So, last winter I bought a heating cable. This year I have more spiders, so need more cable, but I have no idea what Wattage the one is I already have.

The only markings on it is a light blue line that runs the length of the cable.
It doesn't heat up a hell of a lot.

Is there a heating cable standard? Blue for 20W, Red for 100W? Any ideas?

Doen't matter @ all

27W, if you need a bit more heat 34W.
Not a train smash. You can still connect them together.

If I remember correctly the green heating wire is the lowest heat at 14w, the other colors get hotter. orange is 30w

Duan when you say "connect them together" are you talking about taking new heating cable and connecting to the existing cable or do you mean you can use a 14 watt with a 30watt on the same rack running next to each other?

Thanks Jake. The plan is to build a couple of 1.5m x 1m shallow boxes with heating cable sitting on foil for behind the open shelving in my open plan home office. Just to take the edge off the cold at night. Basically a big-ass heating mat.

The blue wire I have is too cool, so if I know what it is, I can adjust upwards.

Jake wrote: If I remember correctly the green heating wire is the lowest heat at 14w, the other colors get hotter. orange is 30w

Duan when you say "connect them together" are you talking about taking new heating cable and connecting to the existing cable or do you mean you can use a 14 watt with a 30watt on the same rack running next to each other?

One shelf 27W another shelf 30w etc. And connect all with a chocolate box into one wall socket.

Mine been running that way for esveral years now without issues

Duan wrote:

Jake wrote: If I remember correctly the green heating wire is the lowest heat at 14w, the other colors get hotter. orange is 30w

Duan when you say "connect them together" are you talking about taking new heating cable and connecting to the existing cable or do you mean you can use a 14 watt with a 30watt on the same rack running next to each other?

One shelf 27W another shelf 30w etc. And connect all with a chocolate box into one wall socket.

Mine been running that way for esveral years now without issues

That why I asked, as joining a 27W to a 37W heating cable together which is a no no and can cause problems.
Even cutting and joining the heating wire is a big no no as well, you have to use the full length of the wire.

As it is sold in that length for a reason.

And exactly as you have done is the right way.

Just need to consider attaching a thermostat in line, that if you don't have one all ready.