I also have a tonne of stuff running on a single, fanless server via docker compose. It is amazing, barely breaks 20% CPU, better uptime than aws ;-) ... One overlooked aspect is that if you use something like my Streacom db4 case, beautiful, fanless, noiseless, you can put it in a living area. Depending on where you live, the power usage can be fully offset against heating costs for your home, making it very efficient.
Just a note on power consumption with regard to heat output. Electric resistive heating is 100% efficient with regard to electricity from the socket. This is the upper limit on efficiency for a computer. This ignores efficiency losses from transmission and from electricity generation. If your electricity is generated by fossil fuels, you are getting much less than 100% efficiency from the energy stored in those fuels.
Heat pumps can achieve greater than 100% efficiency relative to electric resistive heating, because they move heat, rather than do work to create heat. These can achieve equivalent heating at 50% of the electricity utilization compared to resistive heating.[0]
Local fossil fuel heating (e.g. natural gas furnace) is much more efficient than electric resistive heating. The efficiency of local fossil fuel combustion is close to 100% of the energy content of the fuel, as it is turned directly into heat and that heat is dissipated into the home. More than 60% of the energy content used to generate electricity is lost in the generation process in the US.[1]
So, the heat from a computer does offset heating costs, but at less than 100% efficiency. For a small fanless machine, this is not likely to be a large expenditure, but it is valuable to keep in mind that heat from electronics is not "free".
