A room's thermal mass allows it to capture sun's energy

Q. I feel the sun shining in a living room window and it's very warm. My budget is pretty tight, but I want to make or install something to capture that heat and lower my heating bills. What do you suggest?

A. All of the heat energy we use in our homes comes directly or indirectly (gas, oil, coal, wood, etc.) from the sun. Some of it, such as oil, gas, coal, has stored the sun's energy over millions of years. Trees store it for decades until we burn them. Passive and active solar systems use the current sun's heat as it shines on houses each day.

Just having the sun shine in a large window is effective passive solar heating, but it can be made more efficient. This type of solar heating is especially efficient in warm southern climates where the winter days do not become as short as in northern areas. Also, since it is warmer outdoors in mild climates, less heat is lost back outdoors through the window at night.

To be most effective in every climate, there should be adequate thermal mass in the room with the window. This thermal mass captures the sun's heat so the room does not overheat or lose as much of the heat back outdoors again. Once the thermal mass warms up, it slowly dissipates the stored solar back out into the room once the sun is no longer shining in.

If your wife is not really into Flintstonesque decor with a pile of rocks in the center of each room, there are other methods to increase the thermal mass in a room. It is preferable to have the thermal mass in the direct path of the sun's rays, but this is not critical to be effective.

Planters can be made with concrete blocks or bricks. You can also pour and make your own concrete planters using tinted concrete similar to contemporary concrete kitchen countertops. A large terrarium with much damp soil has a reasonably high thermal mass and it adds humidity to the air.

The best solar option, if you do not need a view outdoors from the entire window, is to build a solar Trombe wall. A simple design uses stacked bricks or concrete blocks very close to the window. The vertical stack gets warmed by the sun and this creates an upward warm air current. This circulates the warm air throughout the room while it also stores heat for the nighttime. During the summer, just remove the bricks or blocks and store them away.

If you want to keep the view from your window, make a shallow flat solar heater that rests against the outside wall facing the noon-to-afternoon sun. A size of 4-by-8 feet is good because it makes the most efficient use of inexpensive standard lumber. The box has to be only the depth of standard two-by-four studs.

Once a plywood box is completed, paint the inside flat black. Cut one hole in the back at the top and one at the bottom and install duct stubs. Cut holes in your house wall so the duct stubs come through to indoors. Cover the front of the box with a sheet of clear acrylic plastic and seal it. Make airtight indoor covers to seal off the duct stubs at night.

Q. I have an outdoor wood-burning boiler with a heat exchanger in my new propane furnace. It seems like the blower lets the room temperature drop too much before coming on. What is wrong with the new furnace?

A. There probably is nothing wrong with your new furnace. The blower is controlled by the wall thermostat and the air temperature inside the furnace. The furnace has a sensor so the blower will not come on until the burners heat the air enough.

Contact your furnace installer and have the wall thermostat checked. Also, the sensor inside the furnace may be adjusted so the blower comes on at a lower temperature.

• Write to James Dulley at 6906 Royalgreen Drive, Cincinnati, OH 45244.