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Thermal Control

Why Insulate?

Why Heating Can Be Expensive
During cold seasons, convection currents carry heat up to the top of your living areas. Your ceilings then conduct the heat to your attic where the process repeats and heat eventually escapes to the exterior.

Why Cooling Can Be Expensive
During hot seasons, the Sun radiates heat to your roof which conducts and radiates the heat into your attic and ceiling. Your ceiling then conducts and radiates heat into your living spaces.

There are many reasons to ensure a building is well insulated. Reducing winter heating costs quickly springs to mind, but summer cooling savings can be even greater because it's much harder to remove heat than create it.

Quality insulation creates buildings that are evenly heated, free of hot and cold spots, free of drafts and generally more comfortable to live and work in. Heating and cooling equipment will have a lighter workload and often require less maintenance and repair work. Thermal insulation also has sound absorbing properties which can reduce outside noise.

Heat Migration

The primary function of insulation is to prevent heat migration. This means keeping heat inside your home in winter and keeping it out during the summer. Heat can escape or enter your home via conduction, radiation, convection and air leaks.

Here's how these processes result in heat migration:

  • Convection is the movement of heat in a gas or liquid. As air gets warmer it gets lighter (technically it becomes less dense) and rises. Hot-air balloons demonstrate this effect nicely – the hot, low density air in the balloon provides a lifting force. In your home, warmer air carries heat upwards, leaving lower levels cool and upper levels overly warm.

  • Conduction is the transmission of heat through a medium. Metals are very good conductors. Anyone who has touched a hot saucepan knows that metals conduct heat quite efficiently. In your home, heat can be conducted through walls, floors, ceilings, windows, and doors.

  • Radiation is how heat jumps between two separate objects. This is how heat from the Sun crosses space to reach us here on Earth. The Sun heats your roof, which then radiates heat across your attic and heats your ceiling. Some of that heat then radiates to objects in your living spaces.

  • Air leaks allow heat to hitch a ride on air which can sneak in or out of your home through gaps, cracks and crevices. A common culprit is gaps around door and window frames which may not fit snugly into their cutouts.

All this heat migration costs you money because it's wasting energy that you have paid for. Winter heat loss results in your furnace working harder and burning more fuel in order to keep you warm, while in summer, your air-conditioner slogs away to keep you comfortable.

How Insulation Works

Insulation drastically slows the migration of heat with thermal barriers and air seals. A thermal barrier prevents heat from traveling through walls and ceilings, often using materials that trap air to resist heat conduction. This resistance to conduction is known as R or R-Value. A higher number indicates better resistance (see below for a detailed explanation).

Air sealing prevents the movement of air though gaps and crevices. Air sealing is particularly important around doors and windows where gaps may exist between frames and wall structures, but the structures of homes and buildings are rife with small openings. Such gaps allow air to leak in and out of your home, carrying heat along with it.


R-value, or Resistance Value, is well-knows measure of a material's thermal resistance. Unfortunately, R-value is commonly viewed as the only measure of an insulating product's effectiveness, but it is, in fact just one of several factors. A high R-value is good. The higher, the better. But, if air can move around, or worse, through an insulating material, that R-value means nothing because all that air you've paid to heat (or cool) is drifting away.

R-value is determined by measuring the amount of heat energy able to pass through a material. A higher R-value indicates more resistance to heat migration, but the test is conducted in carefully controlled air-tight laboratory conditions so that the result is not influenced by other factors. Laboratory tests exist to measure these other factors, but R-value became a stand alone measuring stick long ago and . Your home (or office building or whatever) in the real world, where wind blows and where walls aren't sealed up like a space ship.

R-value was created as means to evaluate insulation. It has been in use for more than half a century, but despite the fact that it is now known that R-value should only be considered in context with other factors – air permeance for example – R-value is still used as a stand-alone measuring stick. For more on this, read The R-value Fairy Tale by David B South, reproduced right here on our site.

If you're an algebra buff, the actual equation for R-value is R = A x dT ÷ Q, where A is surface area in square feet, dT is the temperature difference in Fahrenheit and Q is the heat flow in BTU per hour.

RSI is the metric measurement of thermal resistance. To convert R to RSI, multiply R by 0.1761. To convert RSI to R, divide RSI by 0.1761. The Ontario Building Code minimum standard of R-40 is equivalent to RSI 7.0.

Air Leakage

Air leakage refers to the movement of air into and out of a building through cracks and holes in the building envelope. Formally known as “infiltration” (incoming air) and “exfiltration” (outgoing air), air leaks cause drafts and drive up energy costs for heating and cooling.

Home Foam® Inhibits air leakage and can have a huge impact on energy use in both summer and winter. Even a well-made house or building will have myriad gaps, holes and crevices – joints between wall panels, holes bored for pipes and wires, gaps between walls and the roof, etc. – but Home Foam® effectively plugs these gaps thanks to its expansion process.


Choose Home Foam® for health, comfort and energy savings

Web site by Mark Jackson