How to Choose the Right Thermal Wall Design

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Although thermal Trombe walls work well in all climates and for almost any home, you need to choose the correct design for your particular needs. This choice depends on your local climate. Here are some essential guidelines:

Severe cold

In regions which have a moderate to severe climate, you will need to install the thickest, toughest Trombe walls. They must be angled as close as possible to true south, and use the lowest possible U-value glass, double glazed. Windows can be used for immediate solar gain rather than installing vents (which are difficult to control in very cold climates).

Very cold climates also demand selective surfaces on the exterior of the wall to get every last therm of energy out of the sun's light. Construction of the wall should also concentrate on shutting out every leak and reducing conduction losses to a bare minimum. The interior finish should provide the smallest possible barrier to heat transfer.

External insulation is also a good idea, especially if you opt for reflective panels that lie flat during the day and bounce even more sunlight onto the wall. The panels can lie on a wooden frame to protect them from damage, and should be tilted 5° or so away from the house to ensure any moisture drains away from the foundations. You can get an additional 30% to 40% solar gain by installing these panels, which also help if your Trombe wall is shaded by trees.

When installing in extreme climates, you will need to build thicker walls, aiming at the 24-inch end of the scale.

Moderate cold

As winter heating demands drop, so the need for optimizing efficiency falls away. You still want to angle the wall as close to true south as possible and use double-glazed, low U-value glass, but you may be able to do without the insulation or go for a simpler option. Leaks and conduction losses should be minimized in the same way as for severe climates.

Windows and venting can be used for direct solar gain in moderate climates, though venting is a tradeoff. The more immediate heat you pull into the house via the vents, the less will remain to keep the rooms warm at night. In most cases, it's best to go with windows for immediate warmth, as they are more efficient and do not have the down-sides associated with venting. Just make sure the windows don't leak!

Mild climates

The important part of Trombe wall installation in mild climates is to ensure the overhang keeps the summer sun off the wall as much as possible. Once that is achieved, you can probably get away with single-pane glazing.

Windows and vents can be used as in moderate climates, though venting is less of an issue because outdoor temperatures are warmer. Windows work well for immediate, direct solar gain, as always.

In mild climates, Trombe walls act as storage heaters for nighttime more than anything else, so they are simpler to install.

How to size the wall

A Trombe wall can be sized depending on your location's latitude and