I run my rig with 7870 and 5770 during the cooler months(Im Ireland so similar climate) and it does a great job of heating my room(a lil box of a thing). Just in the process of recalibrating my setup atm but I can set them low when Im sleeping and its just a small hum. Cant run it weekends when the girlfriend is here but two bodies is enough to heat the place ok then. Also have a second box that runs under the desk 24/7 as a sort of home server, so thats constantly pumping out about 100W or so.

Thinking about an extra fan blowing onto the cards so I can slow down their own fans a bit more and manage noise.