99% of people will be better served by a single consumer PC instead of enterprise gear, don't convince them to buy a poweredge!

Apart from eBay and specialized reseller websites you can actually find some good deals on used enterprise gear onAmazon through third party stores. I've bought a few different things and had excellent results universally. The real trick is just knowing what to search for, which servers or computers are popular in enterprise and on the end of their lifecycle. Dell, HP and Lenovo servers and mini PCs that are sold to enterprise and are a couple generations old are what to look for.

I got 3x Dell R720 2U servers off ebay a year or so ago, they were $300-ish landed. Dual 6 core CPUs, 256GB RAM, no drives. I got 2 of them for work for our dev/stg cluster, and the price was so good I decided to get one to set up a homelab.

With these kind of servers you want to look at the idle draw. As a homeserver that is probably your 80-90% use case. Some of them draw a significant amount at idle as they are not configured to run that way. The next thing to look at is fans. They can be rather loud (but can sometimes be configured to run slower and less loud). Also many of them are rackmount items. So you will want to think about how to stack your machines. You can buy used racks or a halfrack or just dump them on a table somewhere. Also sometimes you have to worry about the power supply. Sometimes they use different power cables than what a normal house would use.

I personally moved about 10 years ago to a very simple setup using a intel nuc. The idle is in the 5-10w range and max 45-65. I was using something that was idle 100-200. It shaved off about 15-30 bucks off my power bill per month when I did it plus a couple of other items in the house that had very poor idle. I am planning to move back to something a bit more interesting. But the specs to keep an eye on is the idle and max draw. For me I want something modest. But if you go all out and drop a couple 4090s in there and a decent xeon or threadripper it can get up there. Also keep in mind some of them have extra interesting things like fiber channel cards or some sort of infrastructure fabric ports (or lots of sata). They are not 0 but do add into the cost. So you may want to look how to disable them if you are not using them.

So something that is ide 5w would be about 5 dollars per year idle and about 65 form my max load. My price per kwh is 11 cents. Pretty sure the formula is ((number of watts)/1000)24365*(price per kwh). That should get you the yearly cost. Just run the calc for max and min load.

So you may be better served buying something newer that uses less power in the long run. Short term though playing with old hardware can be cost effective and fun.

It extremely depends on how old the thing is. Generally the older they are, the more power they take. Machines were not efficient back then.

I have a poweredge from 2015 or so. Dual Xeon processors and all. It tops out at 500W absolute max. Though, idle is at least 75-100W. It's not too bad, I think I calculated <$100 a year. Obviously you can get some amount of virtual server for that much money, but I like being able to lay hands on a physical box. Plus the blinkenlights and HDD chatter noises are nice.

In my experience, power is not the issue; it's the noise. Servers are LOUD.

If you're getting one that requires 3-phase power, you should probably think again. :-)

You'll find them readily available on Ebay, but there are also multiple companies that specialize in refurbishing servers (which usually will allow you to configure your actual needs - but this will be slightly more expensive in my experience).

Someone just moving decommissioned servers from a data center to new users without doing anything with the equipment in between allows you to find decent deals if you're looking for something to put in a rack.

Be aware that rack servers are usually rather power hungry, so they might be expensive to run over time.

Should you know any former CTO's or technology entrepreneurs you could ask them?

As one myself I possess pallets of nearly new equipment that had zero issues in function and was only decommissioned per security compliance requirements involving End Of Life equipment. Many informed consumers are now complaining about the forced hardware upgrade for Windows 11 but this EOL revenue technique has existed for decades given Payment Card Industry (P.C.I.) compliance.

On supermicro boxes, one can download their IPMI configuration utility to adjust fan settings from full-blast to temperature-controlled, which reduces the noise to tolerable levels so long as it's not running at 100% load all the time.

On Dells this can be done in the BIOS.

The Dell machines can be quite quiet if you don't run them to full capacity. I have one in my office and it's basically silent.

And if it's still too cold, start mining bitcoin?

https://heatbit.com/

I have a hybrid water heater that uses a heat pump to suck heat out of the air to warm my water.

I placed my homelab next to it so that at least my waste heat gets used in the most efficient manner that I have.

I guess... I have mine in a fairly small room and that room definitely gets warm, but actually harvesting that heat in a meaningful way in a useful room I dont think so.

It's not as efficient as a heat pump nor as cheap as burning natural gas but yeah you can use it as a space heater

That depend on context. Is it your own rack in your own data center or rented space in someone else data center? A rack in a AC cooled office room? What uptime is required? What redundancy is required? What are the network requirements? Any environmental concerns (power loss, flooding, extreme heat overpowering the ac, travel distance for personal)? How do you want to manage personal during night/weekends/holidays? What is the distance to shops that has spare parts? Access to backup power?

Most of it can be fairly simple to solve or risk manage if the company is small, people are flexible, and the uptime requirements are not that strict or there is sufficient backup solutions. If its just owning your own rack in a rented space in a data center then the difference is fairly minor, as well as the cost savings.

Agreed! And there's this space in the middle there...Because at the dayjob/enterprise side of things there's the concepts of hypervisor vendors, CoLos (co-locating servers in data centers), and full-blown enterprise on-premise...and of course other end of spectrum is homelabbing/that is self-hosting stuff at home either on consumer or old server grade computers...but what if i want to have a single server for my own self-hosting use but in a tiny data center/colo, but which is not outlandish, and i would maintain it myself? I dont know what we'd call that space: mini-CoLo, or self-data centering, or remote-homelabbing? but, i'm sure there's a gap in knowledge there, and would be great to learn more. :-)