I have a 2000w baseboard on a double pole thermostat. It wasn't providing enough heat for the room size so I installed an additional 1500w on another wall. I wired it to the to the main baseboard opposite end from where it is wired to the thermostat with #12 with run of about 16'. They are both getting warm but not hot. What could be wrong?
Thanks

Sounds like you wired both units in series. Needs to be wired in parallel.

If you butted new heater next to an existing, and spliced wires together in both ends next to each other, that's what happened. Some how you need to get the feed cable supplying the other end of the existing to the new unit.