The boiler has never fired at night, even at -15C = 0F outside - the slab never cools fast enough.
That was my point.
The automatic valves that I've seen are all related to regulating water temperature into the slab. The plumbers are following the manufacturers instructions when the use a pump on a main loop, but tmtowtdi (there's more than one way to do it).
The plumbers I work with keep the water temp going into the slab at about 120F. Higher than that damages the concrete, they say. The heat loss from the slab keeps the surface temperature at about room temperature, but I suppose if the dog was too stupid to move, it would get a little warmer under him. I'll keep the 100w/m sq in mind. Thanks for that.
The recuperating ventilation system, called air to air heat exchangers here, are required in our building code. It replaces exhaust fans in bathrooms, laundry rooms and kitchens and is interlocked with the forced air system. Everything helps.
I'm not a fan of CFL's, although I use them. LED's are way cooler.
