[randen]

From experience we have in our home a heated slab of concrete 6 inch th. finished with ceramic and porcelain tiles. We began heating it with a oil-fired hot water tank. It worked very well. The input temp was 180 degF and the circulating pump ran and stopped keeping the floor at a constant temp. and it was very comfortable. During the winter months and as the price of oil began to shoot up I noticed the oil burner seemed to run a long time. Makes sence. The flue gasses flowing up the stove pipe in the furnace room made the room quite warm. It made me think! there is a lot of heat going up the chimney. If I only need the floor at 85 degF and for showers only 105 degF why am I heating the water to 180 degF. I lowered the temp on the water heater to 110 degF the house stayed as warm and we didn`t notice the difference with the showers but the oil consumption dropped way down and the furnace room was no longer like a sauna. The oil burner ran a lot less.

Long story short. Lower temperatures mean lower losses. The little circ. pumps are designed for continuous operation and are very inexpensive to operate.

We are now heating with solar hot water and geo-thermal which never exceeds 106 degF
The tubes in the concrete are 12 inch centre to centre and .62 inch dia.

However this is an older technique, better is as Mikesolar states smaller tubes placed closer together 4-6inch and closer to the surface to be heated. I had also learned by experience heating between the floor joist below the plywood dosen`t work. The tube needs to be placed on top possibly in a routed groove and covered with a flooring that will conduct heat like ceramic tile or a thin hardwood, but never carpet. Check (Uponor)

Randen