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What Are the Sources of Home Heat Loss?

Lindsay Wilson's picture
Shrink That Footprint
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  • Nov 28, 2013

Heat losses

In the first post of this series I mentioned that the thing that you are really paying for in your heating bill is heat loss.

All a heating system does is top up heat that is lost over the course of a year.

Where heat is gained and lost

Because a house remains roughly the same temperature over the course of a year its heat gains are equal to its heat losses.  We can thank the first law of thermodynamics for this.

Heat gains come from heating systems, the sun’s warmth and internal gains from things like appliances and body heat.  Heat losses occur through convection in the walls, floor, roof, windows and doors or via ventilation in the form of air leakage.

In the image above I’ve shown the typical shares of heat gains and heat losses for an average European home.  The major sources of losses are walls (35%), roof (20%), windows (15%), ventilation (15%), floor (10%) and doors (5%).

When you see figures like this it is important to remember they are only generalizations.  If you live in an mid story apartment with neighbors above, below and to your sides, your floor and roof heat loss will be non-existent. Windows, external walls and ventilation will instead dominate heat loss.

Reducing heat loss reduces heating needs, and hence bills.  This can be done by improving the insulation of your building’s envelope, improving air tightness or turning down the thermostat.

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John Miller's picture
John Miller on Nov 27, 2013

Lindsey, another major factor that affects one’s heating bill during the winter is the internal average temperature setting of the residence.  Thanks to the 1st law of thermodynamics those who set their home internal temperatures lower such as 20 degree C vs. 24 degree C could experience 20+% lower heating bills then those who prefer higher temperatures.

Gidon Gerber's picture
Gidon Gerber on Nov 27, 2013

Somewhat counter-intuitively, opening the windows once or twice a day for five minutes can also reduce your heating bills.Warm and moist air will be replaced by cold, dry air. Colder air holds less moisture than warm air and takes less energy to heat up and keep warm. It’s better for your heating bills and for your health, as you avoid problems with condensing moisture and possible growth of mold.

Even better of course are ventilations system which recuperate the energy from the warm air, as they used in modern passive houses.

Another alternative is to use heating systems which have a higher proportion of heat radiation, compared to convection. Heat radiation does not warm the air, it passes through the air to heat just people and surfaces – like sunshine on a cold day. If you have radiative heating, the air in the house can be colder and you can still feel comfortable.


Pete Stiles's picture
Pete Stiles on Nov 28, 2013

The heat loss through walls is conduction not convection as stated. In fact provided there are no holes in any interior to exterior part of the biulding then convection plays little part in losses.

donough shanahan's picture
donough shanahan on Nov 28, 2013


If you live in an mid story apartment with neighbors above, below and to your sides, your floor and roof heat loss will be non-existent.’

Just nitpicking but while I know what you are getting at, the above is not quite true. For example if the people around you have their heating set higher than yours, then you will find you need to use less and if you are the hot one, then your losses will be decreased significantly but no zero (unless they are unoccupied).

I only ever noticed then when I was the cold one. My heating would kick in at 19C or 20C but as my neighbours, below, above and to two sides were set higher (one was on 25C), my heating certainly was not excessive.It is an excellent way to reduce energy overall.


Lindsay Wilson's picture
Lindsay Wilson on Nov 28, 2013

Thanks Pete, that is quite a typo.  Just fixed it on the original

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