I do this. If you want to actually want to use or donate the processing power, this is kind of a good thing. However, there are a lot of downsides:

• Computers are generally much lower power than a heater. This makes them very slow to “react” to heating needs. Heating a small room, even with a 500W PC, could take an hour or maybe more.
• Heaters have a thermostat, which computers don’t, so even though they are very laggy, they also don’t stop heating when the temperature is right. This means they can overshoot and make the room uncomfortably hot.
• You could set up an external thermostat but then you need a load which can be switched on and off.
• I was using folding@home, but the work items take a long time, and switching them on and off will increase the time taken to resolve the work item, which in turn means the system could get annoyed and use someone else’s computer to resolve the work item faster, or worse, blacklist your computer.
• Using your PC to generate heat will use up its maximum lifetime. The fans aren’t built to be running at max speed all the time, the CPU & GPU could wear out, and the power systems will also wear as time goes on. You sort of have to align that lifetime against usage. This is likely fine if you see the computation as a donation or if you have important stuff to compute, but it’s probably not worth just wasting the cycles.

Sure the Processors can get hot. But is it enough to heat a room tremendously for your needs? I somehow doubt it.

You would need to retinker the Heat spreader on your cooler.

Anecdote:

I have a server running 24/7 in my office, drawing 120 watts average (tested). Office is 10x10. It alone keeps that room 2-5 degrees warmer than the rest of the house. If I turn it off, room equalize to house.

As for comparison, those little square plug in space heaters consume 500 to 1500 watts, and you can see how much th heat.

1 watt = 3.4 btu

Depending on your use case, why not look to reduce power consumption? I’ve replaced that server with one that draws <20w at idle. That’s negligible.

You could probably mod a water cooler system to connect to a water to water heat exchanger like this: https://www.heata.co/

In general, like others have said, lots of humidity is bad for the hardware, you will need to separate this somehow. But heating a small grow-room with an extension of a CPU water cooler might be possible.

I miss the GPU mining days from long ago. Used to have a five old computers with potato GPUs on a time switch to do just this or folding at home as a fun experiment many years ago. It kinda worked in the earliest days but asics killed the income offset after a few months.

The old Core 2 Quad Dell with three dvb-t tuners and a few hard drives still dumps a fair bit of heat into the room.

This is actually a really bad idea.

At “best”, your server is a resistive heater. Aka “a space heater”. Except that your server also has hardware designed to convert power into negative temperature (you know… fans). So you are at a lower efficiency than the space heater in the corner.

Also? Computers aren’t meant to run all that hot for all that long. Yes, the safe margin for hardware is a lot higher than people would think. But if you want this to make a meaningful difference you are going to be running REAL hot for extended periods of time. Because you don’t need heating when it is warm outside. You need it when it is cold and you are already going to be fighting a low ambient temperature.

The reason this works for larger data centers and specialized installations is that they are designed with this in mind. You generally either have direct water cooling of the racks (plural) or you have “water cooling” of the server room itself. With the water then being recirculated amongst the radiators in the building itself. And… those are quite often borderline “scams” because they don’t actually keep the building all that warm in the winter (as discovered during The Pandemic when the lack of body heat from human beings caused issues for a lot of hybrid office/data centers) and they mean more HVAC costs to keep the building cool during the summer.

Which gets to the other aspect. Are you going to change all your fan and cooling settings on a weekly (or even daily) basis? Because maybe you want to get right up to thermal throttling during the winter because the ambient temperature means that heat will “dissipate” fast. But during the summer or even a warm winter day? You are turning your server room into the kind of inferno that even Tom Cruise has someone else deal with.

Don’t get me wrong. Having a chonky and inefficient PC is great for late night gaming in the winter when you should have gone to sleep hours ago and your zone is already set for the “nobody but the cat is in there” setting. But, even at the datacenter level, it is not a good replacement for HVAC. And, as a lot of us will attest: Summer is when you grab the Steam Deck or go downstairs and use the xbox.

Computers are just heaters that do maths as a side effect, so it makes sense. There’s even a company monetising the idea for ESG credits

Two issues i can see are

• Humidity in a grow room will be bad for a computer
• With modern computers the heat output will in part depend on the workload, so you will need to find a way to make the computer do more work when you want more heat.

I run a quite powerful server rack for my business (two servers with 64 core Threadrippers, redundant power supplies, nice SSDs, etc) and it puts out some heat, but not even as much as my gaming PC. The CPUs are usually sitting near 2% utilization, so it’s barely drawing any wattage, and thus, barely putting out heat. So it really depends on how much the server is doing that will determine the heat it outputs. You can build a 1000 watt server, but if it’s only drawing 50 watts, it won’t be generating much heat.

That being said, if the alternative is an electric heater, then using a server for something productive like BOINC or Folding at Home is a better use of your electricity, and may produce the heat you’re looking for. And for your use case, an older (and thus cheaper) CPU would probably suit you, so win-win.