OK, as I'm feeling nice...
I mentioned the seals in the climate control system because there is foam around the various doors in the system. If it wears out, you'll get hot air, drafts from the outside, etc...
Anyway, if you're not at the lowest temp on the climate control, the blend door opens to allow some heat. This is why I thought he might not have A/C as if the A/C system is functioning well, you don't really notice the heat part...if the A/C isn't working correctly (or at all), you'll get a lot of heat.
The same goes for the highest temp on the climate control (with the A/C working and on), you'll get cold air mixed with the hot air. If the valve on the firewall is closed, then you get lots of cold air.
It's really not that hard...