what

When an appliance (or really anything you plug into the wall) consumes electricity, you get heat - regardless of what else that device is also doing.

The reason for this change in temperature is the transformation of electric energy passing through the conductor into heat energy.  This effect of electric current is called the heating effect of current. 

This heating effect is used in many appliances today, whether it's an oven, electric baseboards, a space heater, a stove, a water heater, toaster, hair dryer, iron, etc. - "resistance" heating is a timeless way to turn electrical current into heat.  Although resistance heat is perfectly efficient at converting electricity into heat, more cost-effective ways of generating heat have gained popularity; including the combustion of natural gas, and heat pumps.  Many of course also combust other energy-dense and cost effective fuels, such as wood pellets.

Many of us are also familiar with the notion that computers produce heat.  Generally, this heat is a nuisance and if not properly moved away from a machine (usually via fans), it can become a threat to the equipment itself.

However, if one has an applied use for the heat that is generated from an electrical process, opportunities arise.

Enter bitcoin mining.

In short, we are using the heat from a computer to heat a pool.  Traditionally, the most popular ways to heat a residential pool have been either via a solar thermal setup or via combusting gas (propane or natural gas).  Both have their costs (fixed and variable), and also constraints (physical footprint, weather dependencies, etc.).  When we heat our pool with a bitcoin miner, the concepts of cost and constraints remain applicable, but enable us a different tool in the bag to optimize our for costs and heat output.

Upfront cost

Variable cost

Other considerations