My homelab runs on two T20's. 24/7/365 without issue and they sip ~ 25 watts from the wall with Xeon E3 L-series chips.
They are pretty old though and just barely fast enough. Last year I ordered a Precision 3630 to test out as an upgrade. I was so disappointed by the engineering and build quality I requested a return the day it arrived.
I had a T30 that ran 24/7 for about 10 years but started having machine checks, but I was too lazy to see if it was fixable, so I just bought the T40 to replace it. The T30 was a solid machine and I never had a problem with it. I can start to hear some fan bearing failure now in the T40, which means they're not using ball bearing fans and that really pisses me off.
They are pretty old though and just barely fast enough. Last year I ordered a Precision 3630 to test out as an upgrade. I was so disappointed by the engineering and build quality I requested a return the day it arrived.