At the moment I'm using a 13.5W heat mat under a wood viv. It's on 24 hours with an incandescent bulb on for 12 hours during the day. The heat mat on it's own is not keeping ambiente temperature up quite enough at night. Would a 20W mat create more heat? My daytime temps are fine at the moment - would a 20W mat maybe bring my daytime temps too high?

Also my humidity increases from about 50% during the day to over 70% at night. Does anyone else experience this at all? Is it a problem?