My house is 30 years old, I have a Lennox electric heat with air. Everything else is working, but as the temp is starting to drop my furnace does not seem to keep up with set temp. Therefore it is constantly running. Any suggestions?

Just off the top of my head, you could have a failed heat strip or sequencer.

So how do I check that?

Depends. How compatant are you with electricity.

What do I need and what do I check?

Electrical multimeter should get it done.

Don't have one tonight what do I look for tomorrow and thank you so much for your help.