Not exactly what you were asking, but some alternatives.
Here are a couple more ideas for thermal storage that have actually made it into some custom homes. Probably neither of them are worthwhile for existing structures though.
Thermal solar panels to heat a bed of rocks (coarse river gravel) under the home. The system blows heated air thru the rock bed during the day. At night that circulation is stopped and room air is circulated thru the hot rocks.
A 'thermal mass wall' of concrete (or brick) in the living area facing large South-facing windows. At night, thick thermal draperies are closed to block off the windows. The wall then heats the living area at night.
And one more approach that can help in colder climates. This was done in Snow Country in the mountains. The owner bought some styrofoam insulation panels (a few inches thick) that have foil on their surface. He cut them to fit the windows and placed them in the windows at night.
Just for general information, in older houses the greatest heat lose is generally the cracks around the windows and door.
About the same amount is thru the window glass. Double pane or triple pane windows can be a big help, but kinda expensive to both purchase and install. Storm windows on the outside can be a low cost alternative that are effective. Even lower cost is clear plastic sheeting attached on the outside of the building covering the window. Have a few inches air gap between the plastic sheeting and the window and do not completely seal the air space. Have about 6 to 12 square inches vent space to the outside air. This is to avoid condensation collecting in the dead air space.
The third greatest heat loss is usually from the ceiling. Get some insulation up there above the ceiling. If the rafters/joists are accessable, the easiest to use is probably the stuff that comes in rolls, either paper or fiberglass based. If the that space is not readily accessable you can use particle insulation that is blown in, this is not a do-it-yourself job for most people.
Finally there are the walls, treat the same as the ceiling.
Oh! The floor, especially if the underfloor area is open to the weather. Some air circulation is required under the floor if it is above soil, so you can't completely block it off. Your local city building department can likely tell you what the minimum ventilation area is.
Of course heavy carpets with padding will be much help. But try to get some insulation on the underside of the floor if you can. An alternative, and expensive, option is insulate the the living area side of the floor then put a false floor over it. This is hardly ever done, you have to trim all the doors, and if you are really energetic, rip out and reset all built-in cabinets, replumb the toilet and tub, etc.
