I read somewhere that you can actually cut down your heating bills by using bitcoin mining based water heaters or air heaters . Is that possible? Can someone give detailed economics on this ?
More or less... computer chips produce heat, so sure, it is theoretically possible. First you should know that, compared to a heat pump, a miner's efficiency is zero: heat is the byproduct, not the main goal, so it would take much more energy for the same amount of heating than a decent electric heat pump. But since you are generating Bitcoin in the process, we hope it pays off (wouldn't cut down your bills, would increase it instead, but you would have Bitcoins to pay for the increase, hopefully).
The management of the setup and the economics would be hard: an AntMiner S9 consumes 1200W (and consequentially, can heat water by this same amount). You would have to replace the casing and air cooling system with a kind of water cooling system, using water from your hot water tank as cooling fluid.
Then there is the problem: if you water gets to the desired hot temperature, it won't serve anymore as a good cooling fluid. Then you have two options: if you live in a place where bitcoin mining pays off the electric bill, you can mechanically switch the cooling fluid from the hot water tank to an alternative water circuit, this one designed to dissipate the excess heat (an ordinary PC water cooler radiator, for instance), so that you won't have shut down your miner.
On the other hand, if bitcoin mining is economically unsustainable per se, you would have to shut down the miner when the water is hot. In this case, you would have to be sure that the cost of operating the miner minus the bitcoin it produces is lower than operating a regular heat pump (which is more energy efficient, as I said). Not to mention the cost of equipment and installation and R&D to get everything right is much higher with a miner than with a heat pump designed for this purpose.