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Ask the Expert Question-and-Answer Archive

by Ron Joseph

June, 2009

Improving the Thermal Properties of Concrete Walls

Q. I have a concrete walled house approx. 80 mm thick, no air cavity, just the one wall. The ducted heating takes a long time to heat up the house as the cold walls are soaking up the heat from the warm air. If I painted the interior walls with heat reflective paint, would this help reflect the warmth from the ducted heating back into the room? Cheers

A. You've asked a great question, but I don't have a definitive answer. I have to believe that if you coat the walls with a heat insulating paint, you would prevent hot air inside the room from being conducted away though the walls. Therefore, any heat insulating layer applied to the inside surfaces of the walls will lower your heating costs and the room will heat up more rapidly.

I'm not sure how effective it is to apply a heat reflective paint to the walls. We know that the temperature inside the passenger space of white-painted cars is significantly cooler than that for cars painted black. The difference is quite noticeable, but in this case sunlight is being absorbed or reflected. I would imagine that the same principle applies to the painting of walls inside a house, but I don't know to what extent you will notice a drop in your heating bill.

Why not carry out a simple experiment in which you paint the inside surfaces of identical cardboard or wooden boxes with two or three heat reflective paints .. one paint per box. Place a thermometer and low wattage light bulb inside the box and determine the time it takes for the air temperature inside the box to rise to a predefined level.

If the reflective paint really works well, you should quickly see the results in your experiments. My guess is that if you were to coat the sides of the box with an insulating paint, the results would be more dramatic.

If you decide to conduct such an experiment, please get back to me with your findings.


Ron Joseph

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