In fact, there are already a lot of these solutions and I saw the first working projects more than 5 years ago. I think it's easy to find on the internet. The amount of heat generated depends on the amount of mining equipment, but this project requires additional costs, which is not always beneficial.
That's right, I think the cost of installing this type of solution is too expensive for the benefit. If it is to heat the water in a swimming pool, it can be used, but I think it would be too expensive for the efficiency generated. I find it more efficient to use this heat to heat the environment/house than to heat water.
You need to calculate how much money you pay for heating the water in the pool, and how many miners you need to get the same result. If you have video cards, then water cooling for each will be expensive, it is cheaper to immerse video cards in a special liquid that will transfer heat to water through a radiator. But I think that 99% of miners will not do this.