Yes, I'm aware of that.  The S19's are just the first "somewhat suitable" devices I found, but as you say, they are above the power range I think would be reasonable.  I can run the numbers again and maybe I could go with 2000W (or disable some boards as you say), but I was wondering if there are perhaps other devices that are lower-powered out of the box.

However, as stated in the OP, the first priority is using available electricity to produce heat (not the mining itself), so in any case, I would only run the miners intermittently.  And if I run them with 2000W, it means that the water I need heated is done sooner, so it would run for shorter periods of time.  The total energy usage and thus the total hash produced over some time frame would be fixed anyway; so it might not be worth it anyway.

I will need to look closely at the costs of course.  But disabling some of the boards sounds like at least one first potential option to consider, thanks!