[qwert]

Originally Posted by CaberTosser

I've not personally encountered circulators that run on 12V dc, but its plausible that they exist. I would personally seek a standard pump and convert the 12v dc to 120 ac as you will likely need to source replacement pumps in the future, and it would be sensible to keep the cost down.

I am trying to avoid the typical energy loss inside an inverter, as well as the problems of inverted wave shapes. My Grundfos has been in continuous service for >30 years and I would hate to damage it by feeding it a wave form it doesn't like.

Originally Posted by CaberTosser

So far as the 'heat rises' rationale goes, heat spreads through conduction, convection or radiation, you've just planned on convection. Thinking of the earth below as a heat sink is correct, but that can work to your detriment so far as energy consumption is concerned as it will keep on absorbing heat.

When I installed my system there was a lot of variation of opinion and not much experience to provide guidance. It has worked well so far and I am not about to rip it up, if I was doing it today I suspect I would put down a better thermal break, but even dry clay does have an R factor as does the air in the gravel and even gravel acts to slow conduction, and a 55 degree floor is nice in the summer.

My welding experience has been that even conductive heat rises easier and faster than it goes down, which is a major reason we weld thin material down and not up, as it is possible to stay ahead of your heat and avoid burn through.