"You can, but the problem is that warm water isn't that useful." Depends on your other systems. Dishwater wants hot water(but usually has no input for hot wate

"You can, but the problem is that warm water isn't that useful." Depends on your other systems. Dishwater wants hot water(but usually has no input for hot water), washing machine(some do). And if you have a house with 4+ people who like to shower a lot .. it adds up very quickly. And yes, heating. Now are already the days (in europe), with cold nights and mild but sunny days. So .. it makes sense in theory, but not so easy to economically make use of as of now.