Im running almost 40 without fan.. they are costing 0.17 BTC/each, are easy to change if one get burned and i don't want to keep it 10 years up and running.. I prefer to save watts, hub port and to keep everything in silence.. They are hot, but I don't touch them with my tong... so who cares
I hope ours will last long enough to get ROI.
Rough estimations indicates around 3 months to roi according to the currency you're mining.
How long have you been running erupters without fan ?