Not good enough. That won't do at all.

Garters are sun loving diurnal reptiles and garters are also found farthest north than any other snake. Your northwestern really needs the seasonal changes and mediocre conditions don't cut it. They will get depressed, confused, stop eating, then they will waste away and die.

How does he look? is he really skinny? How long has it been since he has eaten anything? Is his skin loose and wrinkled?

Room temperatures since what, last fall? Not good.

I would say if he's not too far gone, you really need to give the snake some exposure to full spectrum lighting. A UVB 2.0 bulb certainly can't hurt. Think bright, natural daylight but with places to hide from the light. A compact florescent UV bulb from a pet store will do for now. Also, it's important to provide just a spot on one end of the enclosure, a basking area about 80-85 degrees. A small basking light or ceramic heat emitter so the snake can warm himself under it but have a choice to go somewhere cooler about 70 degrees.

Seriously, they are very easy to care for once you have a bit of information. If I kept you indoors at those temperatures and you never saw the light of day or warmed yourself in the spring/summer sun wouldn't you get depressed and not want to eat? Think about it.

For the snake, it's been an easy winter. Now spring has sprung. He knows it's about that time. Instead of basking in the sun and getting laid, he's stuck in a closet. Basically, he's in jail. That would be enough for me to lose my appetite.