Ideas for an extra room

[Mike Palmer]

Hello:

I have a unit that has 2 bedrooms/1 bathroom, kitchen, family/front room, and an 'extra' room. It is basically a bedroom (has a window and closet), but it also has a second closet that serves as the utility room. So this room has the furnace, water heater, and laundry in it, and they are only accessible through this room. The door to the room is also louvered to allow for airflow to the mechanicals. But it is a good size room and there is still plenty of space to spare.

I wouldn't use it as a bedroom or sleep in there if I lived there, but wondering what is the best use for this room? It does not have outside access (except via the small window), so I can't think of any good ways to rent it out separately. I usually just advertise it as a 2 bedroom unit with a storage/office/den/extra room, but it just feels like there is so much wasted space. 

Any ideas?