Concept

There are several aspects of radiant heating that make it particularly applicable for solar home heating. First, radiant heat distribution can be designed for lower temperature water. Old cast iron radiators and baseboard, fin-tube distributors rely on 160 to 180 degree or even hotter water for heating. It is very difficult to regularly achieve such high temperatures with stored solar hot water. Not only is it difficult, but trying to do so will lower the efficiency of your solar collectors and in the end you would collect far fewer BTUs.

Secondly, especially in a house where you want to carefully target heat delivery, radiant works well because it is easy to zone and control.

Thirdly, radiant heat warms objects and not the air, so you typically feel warmer at slightly lower air temperatures.

Finally, radiant can be installed in the floor or ceiling. There are a couple of reasons ceiling installation makes sense in solar heated houses: 1) In the Active Area the floor mass will not be heated, which allows it to more effectively capturing solar radiation. 2) In bedrooms, you have carpeted floors and a bed, all shielding you from radiant floor heat. Radiation from the ceiling would warm you directly. Ah, what a concept…

Application

We installed radiant floor circuits in each area of the first floor thermal mass. Sufficient tubing was installed so it will deliver suitable heat with water temperatures in the 90 to 100 degree range. This design is based on more typical insulation levels, so we may find that water as low as 80 degrees provides satisfactory heat when needed.

In our bathroom, on the first floor, we expect to run heated water through the floor each morning so we have heat for showers. By the time we get there, the circulator will already be off.

We don’t expect to heat the Active Area in the morning, though occasionally we will need to. When we do, we circulate heat just in the kitchen area. This area is nearly all indirect thermal mass, meaning that it is out of direct sunlight and it is on the east end of the house. In the morning, when the sun comes in through the main windows it traces an arc beginning at the west end of the Active Area and moves eastward. The warmed kitchen floor will be cool by the time the late afternoon sun gets to it.

In the upstair bedrooms and bathroom, we are installing entirely ceiling radiant heat. We are using a technique presented by John Siegenthaler at a recent energy efficiency conference. John is an author on hydronics and heating consultant. His recommended approach does not require any expensive installation components, just standard sheet goods and careful attention to detail (don’t screw the tubing!).

On the few occasions we want to add heat to an upstair bedroom (kid has warmth loving guest over?), we just turn up the room’s thermostat and within 30 minutes we are good to go.

The upstair bathroom is heated the same way, but automatically with a programmable thermostat.

We may add the same ceiling delivery system to the kitchen to minimize heating the floor mass, if that proves to reduce our overall efficiency. This will depend on how often heat is needed in the Active Area first thing in the morning.

Previous Concept    Back to Concepts Index    Next Concept