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For me the electricity costs in this case are zero or so close to zero that it does not factor.

I put this on an existing server running in my house that runs 24/7 so I am already paying that cost.

The load this adds is as follows. Every 2.5 minutes for 4 seconds there is drive access and a blip from nominal cpu load to about 30% across all four cores.

Given this "server" is the guts of an old laptop with an i5 4200U which has a TDP of 15W at full chat the extra costs are probably not even noticed.

I will have to explore ROI on disks. My current plan is to build a mining PC with the followig

3 * 1050ti Kalmx (Fanless) to mine ETH
1 * Ryzen 1600 (Big fanless cooler if possible)(Mine monaro)
1-2 8TB HDD for Burst

My thinking is if I can get stable and quiet enough this running all three would replace an electric room heater I have, be lower electric cost that the heater and also turn a profit.

Not sure the ROI on it but given triple mine capability and double as room heater that it would be better than normal mining rig ROI :)

Fantastic how we can utilize the waste of one operation to reduce the cost of another. I am in the process of putting together a vertualisation system for a witness. Running it most of the time anyway. Vertualising should make it easy to move to a hosted server once configured.

Do you think the hosting costs are offset by the income from being a witness?

For the heater thing. The reality is if your PC draws 400W from the wall that is the same heat generation as a 400W electric heater. It is just as efficent at turning electricity into heat. So (99.???%)

It is just that in the PC it is producing a byproduct of computation while the heater is just a dumb resistive load.

If it works well and the crypto market stops the current downward spiral I will start to explore how far I can push the idea :)

The Kalmx card is great choice though. My games rig has RX 480 and with the test mining I have done with that it can sound like a jet engine as it has blower style cooler. So I knew I had to explore fanless alternatives :)

The heater thing makes sense in the winter. I need heat anyway but summer will soon be on us and we will be loosing it. In fact may have to get rid of it.

As for the witness thing I am not sure if it would or not. I am looking to move my existing server I host clients on to new provider. convert it from a vps to a cloud system with sever virtual servers. One for the existing hosing system, two for the witness servers. To provide this in two hosted site would currently be about 50 SD each. I think I could do all three for the same price. I already pay 65 Canadian for just my hosting service. So I would be converting from cnd to SD. Know that the usage is low to start and ramps up so I don't need vast resources to start.

Down in NZ so just hitting winter here. Yep, summer I plan on moving the rig to a cooler room we do not use. As long as it covers the power costs then running through summer is not an issue for me unless I have to run extra cooling. For mid summer it might need to be powered down when the ambient temp is too high which would effect ROI. If it can pay the parts in say 9 months then it is viable imho.